1 // SPDX-License-Identifier: GPL-1.0+
2 /*
3  * n_tty.c --- implements the N_TTY line discipline.
4  *
5  * This code used to be in tty_io.c, but things are getting hairy
6  * enough that it made sense to split things off.  (The N_TTY
7  * processing has changed so much that it's hardly recognizable,
8  * anyway...)
9  *
10  * Note that the open routine for N_TTY is guaranteed never to return
11  * an error.  This is because Linux will fall back to setting a line
12  * to N_TTY if it can not switch to any other line discipline.
13  *
14  * Written by Theodore Ts'o, Copyright 1994.
15  *
16  * This file also contains code originally written by Linus Torvalds,
17  * Copyright 1991, 1992, 1993, and by Julian Cowley, Copyright 1994.
18  *
19  * Reduced memory usage for older ARM systems  - Russell King.
20  *
21  * 2000/01/20   Fixed SMP locking on put_tty_queue using bits of
22  *		the patch by Andrew J. Kroll <ag784@freenet.buffalo.edu>
23  *		who actually finally proved there really was a race.
24  *
25  * 2002/03/18   Implemented n_tty_wakeup to send SIGIO POLL_OUTs to
26  *		waiting writing processes-Sapan Bhatia <sapan@corewars.org>.
27  *		Also fixed a bug in BLOCKING mode where n_tty_write returns
28  *		EAGAIN
29  */
30 
31 #include <linux/bitmap.h>
32 #include <linux/bitops.h>
33 #include <linux/ctype.h>
34 #include <linux/errno.h>
35 #include <linux/export.h>
36 #include <linux/fcntl.h>
37 #include <linux/file.h>
38 #include <linux/jiffies.h>
39 #include <linux/math.h>
40 #include <linux/poll.h>
41 #include <linux/ratelimit.h>
42 #include <linux/sched.h>
43 #include <linux/signal.h>
44 #include <linux/slab.h>
45 #include <linux/string.h>
46 #include <linux/tty.h>
47 #include <linux/types.h>
48 #include <linux/uaccess.h>
49 #include <linux/vmalloc.h>
50 
51 #include "tty.h"
52 
53 /*
54  * Until this number of characters is queued in the xmit buffer, select will
55  * return "we have room for writes".
56  */
57 #define WAKEUP_CHARS 256
58 
59 #define N_TTY_BUF_SIZE 4096
60 
61 /*
62  * This defines the low- and high-watermarks for throttling and
63  * unthrottling the TTY driver.  These watermarks are used for
64  * controlling the space in the read buffer.
65  */
66 #define TTY_THRESHOLD_THROTTLE		128 /* now based on remaining room */
67 #define TTY_THRESHOLD_UNTHROTTLE	128
68 
69 /*
70  * Special byte codes used in the echo buffer to represent operations
71  * or special handling of characters.  Bytes in the echo buffer that
72  * are not part of such special blocks are treated as normal character
73  * codes.
74  */
75 #define ECHO_OP_START 0xff
76 #define ECHO_OP_MOVE_BACK_COL 0x80
77 #define ECHO_OP_SET_CANON_COL 0x81
78 #define ECHO_OP_ERASE_TAB 0x82
79 
80 #define ECHO_COMMIT_WATERMARK	256
81 #define ECHO_BLOCK		256
82 #define ECHO_DISCARD_WATERMARK	N_TTY_BUF_SIZE - (ECHO_BLOCK + 32)
83 
84 struct n_tty_data {
85 	/* producer-published */
86 	size_t read_head;
87 	size_t commit_head;
88 	size_t canon_head;
89 	size_t echo_head;
90 	size_t echo_commit;
91 	size_t echo_mark;
92 	DECLARE_BITMAP(char_map, 256);
93 
94 	/* private to n_tty_receive_overrun (single-threaded) */
95 	unsigned long overrun_time;
96 	unsigned int num_overrun;
97 
98 	/* non-atomic */
99 	bool no_room;
100 
101 	/* must hold exclusive termios_rwsem to reset these */
102 	unsigned char lnext:1, erasing:1, raw:1, real_raw:1, icanon:1;
103 	unsigned char push:1;
104 
105 	/* shared by producer and consumer */
106 	u8 read_buf[N_TTY_BUF_SIZE];
107 	DECLARE_BITMAP(read_flags, N_TTY_BUF_SIZE);
108 	u8 echo_buf[N_TTY_BUF_SIZE];
109 
110 	/* consumer-published */
111 	size_t read_tail;
112 	size_t line_start;
113 
114 	/* # of chars looked ahead (to find software flow control chars) */
115 	size_t lookahead_count;
116 
117 	/* protected by output lock */
118 	unsigned int column;
119 	unsigned int canon_column;
120 	size_t echo_tail;
121 
122 	struct mutex atomic_read_lock;
123 	struct mutex output_lock;
124 };
125 
126 #define MASK(x) ((x) & (N_TTY_BUF_SIZE - 1))
127 
read_cnt(struct n_tty_data * ldata)128 static inline size_t read_cnt(struct n_tty_data *ldata)
129 {
130 	return ldata->read_head - ldata->read_tail;
131 }
132 
read_buf(struct n_tty_data * ldata,size_t i)133 static inline u8 read_buf(struct n_tty_data *ldata, size_t i)
134 {
135 	return ldata->read_buf[MASK(i)];
136 }
137 
read_buf_addr(struct n_tty_data * ldata,size_t i)138 static inline u8 *read_buf_addr(struct n_tty_data *ldata, size_t i)
139 {
140 	return &ldata->read_buf[MASK(i)];
141 }
142 
echo_buf(struct n_tty_data * ldata,size_t i)143 static inline u8 echo_buf(struct n_tty_data *ldata, size_t i)
144 {
145 	smp_rmb(); /* Matches smp_wmb() in add_echo_byte(). */
146 	return ldata->echo_buf[MASK(i)];
147 }
148 
echo_buf_addr(struct n_tty_data * ldata,size_t i)149 static inline u8 *echo_buf_addr(struct n_tty_data *ldata, size_t i)
150 {
151 	return &ldata->echo_buf[MASK(i)];
152 }
153 
154 /* If we are not echoing the data, perhaps this is a secret so erase it */
zero_buffer(const struct tty_struct * tty,u8 * buffer,size_t size)155 static void zero_buffer(const struct tty_struct *tty, u8 *buffer, size_t size)
156 {
157 	if (L_ICANON(tty) && !L_ECHO(tty))
158 		memset(buffer, 0, size);
159 }
160 
tty_copy(const struct tty_struct * tty,void * to,size_t tail,size_t n)161 static void tty_copy(const struct tty_struct *tty, void *to, size_t tail,
162 		     size_t n)
163 {
164 	struct n_tty_data *ldata = tty->disc_data;
165 	size_t size = N_TTY_BUF_SIZE - tail;
166 	void *from = read_buf_addr(ldata, tail);
167 
168 	if (n > size) {
169 		tty_audit_add_data(tty, from, size);
170 		memcpy(to, from, size);
171 		zero_buffer(tty, from, size);
172 		to += size;
173 		n -= size;
174 		from = ldata->read_buf;
175 	}
176 
177 	tty_audit_add_data(tty, from, n);
178 	memcpy(to, from, n);
179 	zero_buffer(tty, from, n);
180 }
181 
182 /**
183  * n_tty_kick_worker - start input worker (if required)
184  * @tty: terminal
185  *
186  * Re-schedules the flip buffer work if it may have stopped.
187  *
188  * Locking:
189  *  * Caller holds exclusive %termios_rwsem, or
190  *  * n_tty_read()/consumer path:
191  *	holds non-exclusive %termios_rwsem
192  */
n_tty_kick_worker(const struct tty_struct * tty)193 static void n_tty_kick_worker(const struct tty_struct *tty)
194 {
195 	struct n_tty_data *ldata = tty->disc_data;
196 
197 	/* Did the input worker stop? Restart it */
198 	if (unlikely(READ_ONCE(ldata->no_room))) {
199 		WRITE_ONCE(ldata->no_room, 0);
200 
201 		WARN_RATELIMIT(tty->port->itty == NULL,
202 				"scheduling with invalid itty\n");
203 		/* see if ldisc has been killed - if so, this means that
204 		 * even though the ldisc has been halted and ->buf.work
205 		 * cancelled, ->buf.work is about to be rescheduled
206 		 */
207 		WARN_RATELIMIT(test_bit(TTY_LDISC_HALTED, &tty->flags),
208 			       "scheduling buffer work for halted ldisc\n");
209 		tty_buffer_restart_work(tty->port);
210 	}
211 }
212 
chars_in_buffer(const struct tty_struct * tty)213 static ssize_t chars_in_buffer(const struct tty_struct *tty)
214 {
215 	const struct n_tty_data *ldata = tty->disc_data;
216 	size_t head = ldata->icanon ? ldata->canon_head : ldata->commit_head;
217 
218 	return head - ldata->read_tail;
219 }
220 
221 /**
222  * n_tty_write_wakeup	-	asynchronous I/O notifier
223  * @tty: tty device
224  *
225  * Required for the ptys, serial driver etc. since processes that attach
226  * themselves to the master and rely on ASYNC IO must be woken up.
227  */
n_tty_write_wakeup(struct tty_struct * tty)228 static void n_tty_write_wakeup(struct tty_struct *tty)
229 {
230 	clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
231 	kill_fasync(&tty->fasync, SIGIO, POLL_OUT);
232 }
233 
n_tty_check_throttle(struct tty_struct * tty)234 static void n_tty_check_throttle(struct tty_struct *tty)
235 {
236 	struct n_tty_data *ldata = tty->disc_data;
237 
238 	/*
239 	 * Check the remaining room for the input canonicalization
240 	 * mode.  We don't want to throttle the driver if we're in
241 	 * canonical mode and don't have a newline yet!
242 	 */
243 	if (ldata->icanon && ldata->canon_head == ldata->read_tail)
244 		return;
245 
246 	do {
247 		tty_set_flow_change(tty, TTY_THROTTLE_SAFE);
248 		if (N_TTY_BUF_SIZE - read_cnt(ldata) >= TTY_THRESHOLD_THROTTLE)
249 			break;
250 	} while (!tty_throttle_safe(tty));
251 
252 	__tty_set_flow_change(tty, 0);
253 }
254 
n_tty_check_unthrottle(struct tty_struct * tty)255 static void n_tty_check_unthrottle(struct tty_struct *tty)
256 {
257 	if (tty->driver->type == TTY_DRIVER_TYPE_PTY) {
258 		if (chars_in_buffer(tty) > TTY_THRESHOLD_UNTHROTTLE)
259 			return;
260 		n_tty_kick_worker(tty);
261 		tty_wakeup(tty->link);
262 		return;
263 	}
264 
265 	/* If there is enough space in the read buffer now, let the
266 	 * low-level driver know. We use chars_in_buffer() to
267 	 * check the buffer, as it now knows about canonical mode.
268 	 * Otherwise, if the driver is throttled and the line is
269 	 * longer than TTY_THRESHOLD_UNTHROTTLE in canonical mode,
270 	 * we won't get any more characters.
271 	 */
272 
273 	do {
274 		tty_set_flow_change(tty, TTY_UNTHROTTLE_SAFE);
275 		if (chars_in_buffer(tty) > TTY_THRESHOLD_UNTHROTTLE)
276 			break;
277 
278 		n_tty_kick_worker(tty);
279 	} while (!tty_unthrottle_safe(tty));
280 
281 	__tty_set_flow_change(tty, 0);
282 }
283 
284 /**
285  * put_tty_queue		-	add character to tty
286  * @c: character
287  * @ldata: n_tty data
288  *
289  * Add a character to the tty read_buf queue.
290  *
291  * Locking:
292  *  * n_tty_receive_buf()/producer path:
293  *	caller holds non-exclusive %termios_rwsem
294  */
put_tty_queue(u8 c,struct n_tty_data * ldata)295 static inline void put_tty_queue(u8 c, struct n_tty_data *ldata)
296 {
297 	*read_buf_addr(ldata, ldata->read_head) = c;
298 	ldata->read_head++;
299 }
300 
301 /**
302  * reset_buffer_flags	-	reset buffer state
303  * @ldata: line disc data to reset
304  *
305  * Reset the read buffer counters and clear the flags. Called from
306  * n_tty_open() and n_tty_flush_buffer().
307  *
308  * Locking:
309  *  * caller holds exclusive %termios_rwsem, or
310  *  * (locking is not required)
311  */
reset_buffer_flags(struct n_tty_data * ldata)312 static void reset_buffer_flags(struct n_tty_data *ldata)
313 {
314 	ldata->read_head = ldata->canon_head = ldata->read_tail = 0;
315 	ldata->commit_head = 0;
316 	ldata->line_start = 0;
317 
318 	ldata->erasing = 0;
319 	bitmap_zero(ldata->read_flags, N_TTY_BUF_SIZE);
320 	ldata->push = 0;
321 
322 	ldata->lookahead_count = 0;
323 }
324 
n_tty_packet_mode_flush(struct tty_struct * tty)325 static void n_tty_packet_mode_flush(struct tty_struct *tty)
326 {
327 	unsigned long flags;
328 
329 	if (tty->link->ctrl.packet) {
330 		spin_lock_irqsave(&tty->ctrl.lock, flags);
331 		tty->ctrl.pktstatus |= TIOCPKT_FLUSHREAD;
332 		spin_unlock_irqrestore(&tty->ctrl.lock, flags);
333 		wake_up_interruptible(&tty->link->read_wait);
334 	}
335 }
336 
337 /**
338  * n_tty_flush_buffer	-	clean input queue
339  * @tty: terminal device
340  *
341  * Flush the input buffer. Called when the tty layer wants the buffer flushed
342  * (eg at hangup) or when the %N_TTY line discipline internally has to clean
343  * the pending queue (for example some signals).
344  *
345  * Holds %termios_rwsem to exclude producer/consumer while buffer indices are
346  * reset.
347  *
348  * Locking: %ctrl.lock, exclusive %termios_rwsem
349  */
n_tty_flush_buffer(struct tty_struct * tty)350 static void n_tty_flush_buffer(struct tty_struct *tty)
351 {
352 	down_write(&tty->termios_rwsem);
353 	reset_buffer_flags(tty->disc_data);
354 	n_tty_kick_worker(tty);
355 
356 	if (tty->link)
357 		n_tty_packet_mode_flush(tty);
358 	up_write(&tty->termios_rwsem);
359 }
360 
361 /**
362  * is_utf8_continuation	-	utf8 multibyte check
363  * @c: byte to check
364  *
365  * Returns: true if the utf8 character @c is a multibyte continuation
366  * character. We use this to correctly compute the on-screen size of the
367  * character when printing.
368  */
is_utf8_continuation(u8 c)369 static inline int is_utf8_continuation(u8 c)
370 {
371 	return (c & 0xc0) == 0x80;
372 }
373 
374 /**
375  * is_continuation	-	multibyte check
376  * @c: byte to check
377  * @tty: terminal device
378  *
379  * Returns: true if the utf8 character @c is a multibyte continuation character
380  * and the terminal is in unicode mode.
381  */
is_continuation(u8 c,const struct tty_struct * tty)382 static inline int is_continuation(u8 c, const struct tty_struct *tty)
383 {
384 	return I_IUTF8(tty) && is_utf8_continuation(c);
385 }
386 
387 /**
388  * do_output_char	-	output one character
389  * @c: character (or partial unicode symbol)
390  * @tty: terminal device
391  * @space: space available in tty driver write buffer
392  *
393  * This is a helper function that handles one output character (including
394  * special characters like TAB, CR, LF, etc.), doing OPOST processing and
395  * putting the results in the tty driver's write buffer.
396  *
397  * Note that Linux currently ignores TABDLY, CRDLY, VTDLY, FFDLY and NLDLY.
398  * They simply aren't relevant in the world today. If you ever need them, add
399  * them here.
400  *
401  * Returns: the number of bytes of buffer space used or -1 if no space left.
402  *
403  * Locking: should be called under the %output_lock to protect the column state
404  * and space left in the buffer.
405  */
do_output_char(u8 c,struct tty_struct * tty,int space)406 static int do_output_char(u8 c, struct tty_struct *tty, int space)
407 {
408 	struct n_tty_data *ldata = tty->disc_data;
409 	int	spaces;
410 
411 	if (!space)
412 		return -1;
413 
414 	switch (c) {
415 	case '\n':
416 		if (O_ONLRET(tty))
417 			ldata->column = 0;
418 		if (O_ONLCR(tty)) {
419 			if (space < 2)
420 				return -1;
421 			ldata->canon_column = ldata->column = 0;
422 			tty->ops->write(tty, "\r\n", 2);
423 			return 2;
424 		}
425 		ldata->canon_column = ldata->column;
426 		break;
427 	case '\r':
428 		if (O_ONOCR(tty) && ldata->column == 0)
429 			return 0;
430 		if (O_OCRNL(tty)) {
431 			c = '\n';
432 			if (O_ONLRET(tty))
433 				ldata->canon_column = ldata->column = 0;
434 			break;
435 		}
436 		ldata->canon_column = ldata->column = 0;
437 		break;
438 	case '\t':
439 		spaces = 8 - (ldata->column & 7);
440 		if (O_TABDLY(tty) == XTABS) {
441 			if (space < spaces)
442 				return -1;
443 			ldata->column += spaces;
444 			tty->ops->write(tty, "        ", spaces);
445 			return spaces;
446 		}
447 		ldata->column += spaces;
448 		break;
449 	case '\b':
450 		if (ldata->column > 0)
451 			ldata->column--;
452 		break;
453 	default:
454 		if (!iscntrl(c)) {
455 			if (O_OLCUC(tty))
456 				c = toupper(c);
457 			if (!is_continuation(c, tty))
458 				ldata->column++;
459 		}
460 		break;
461 	}
462 
463 	tty_put_char(tty, c);
464 	return 1;
465 }
466 
467 /**
468  * process_output	-	output post processor
469  * @c: character (or partial unicode symbol)
470  * @tty: terminal device
471  *
472  * Output one character with OPOST processing.
473  *
474  * Returns: -1 when the output device is full and the character must be
475  * retried.
476  *
477  * Locking: %output_lock to protect column state and space left (also, this is
478  *called from n_tty_write() under the tty layer write lock).
479  */
process_output(u8 c,struct tty_struct * tty)480 static int process_output(u8 c, struct tty_struct *tty)
481 {
482 	struct n_tty_data *ldata = tty->disc_data;
483 
484 	guard(mutex)(&ldata->output_lock);
485 
486 	if (do_output_char(c, tty, tty_write_room(tty)) < 0)
487 		return -1;
488 
489 	return 0;
490 }
491 
492 /**
493  * process_output_block	-	block post processor
494  * @tty: terminal device
495  * @buf: character buffer
496  * @nr: number of bytes to output
497  *
498  * Output a block of characters with OPOST processing.
499  *
500  * This path is used to speed up block console writes, among other things when
501  * processing blocks of output data. It handles only the simple cases normally
502  * found and helps to generate blocks of symbols for the console driver and
503  * thus improve performance.
504  *
505  * Returns: the number of characters output.
506  *
507  * Locking: %output_lock to protect column state and space left (also, this is
508  * called from n_tty_write() under the tty layer write lock).
509  */
process_output_block(struct tty_struct * tty,const u8 * buf,unsigned int nr)510 static ssize_t process_output_block(struct tty_struct *tty,
511 				    const u8 *buf, unsigned int nr)
512 {
513 	struct n_tty_data *ldata = tty->disc_data;
514 	unsigned int space, i;
515 	const u8 *cp;
516 
517 	guard(mutex)(&ldata->output_lock);
518 
519 	space = tty_write_room(tty);
520 	if (space == 0)
521 		return 0;
522 
523 	if (nr > space)
524 		nr = space;
525 
526 	for (i = 0, cp = buf; i < nr; i++, cp++) {
527 		u8 c = *cp;
528 
529 		switch (c) {
530 		case '\n':
531 			if (O_ONLRET(tty))
532 				ldata->column = 0;
533 			if (O_ONLCR(tty))
534 				goto do_write;
535 			ldata->canon_column = ldata->column;
536 			break;
537 		case '\r':
538 			if (O_ONOCR(tty) && ldata->column == 0)
539 				goto do_write;
540 			if (O_OCRNL(tty))
541 				goto do_write;
542 			ldata->canon_column = ldata->column = 0;
543 			break;
544 		case '\t':
545 			goto do_write;
546 		case '\b':
547 			if (ldata->column > 0)
548 				ldata->column--;
549 			break;
550 		default:
551 			if (!iscntrl(c)) {
552 				if (O_OLCUC(tty))
553 					goto do_write;
554 				if (!is_continuation(c, tty))
555 					ldata->column++;
556 			}
557 			break;
558 		}
559 	}
560 do_write:
561 	return tty->ops->write(tty, buf, i);
562 }
563 
n_tty_process_echo_ops(struct tty_struct * tty,size_t * tail,int space)564 static int n_tty_process_echo_ops(struct tty_struct *tty, size_t *tail,
565 				  int space)
566 {
567 	struct n_tty_data *ldata = tty->disc_data;
568 	u8 op;
569 
570 	/*
571 	 * Since add_echo_byte() is called without holding output_lock, we
572 	 * might see only portion of multi-byte operation.
573 	 */
574 	if (MASK(ldata->echo_commit) == MASK(*tail + 1))
575 		return -ENODATA;
576 
577 	/*
578 	 * If the buffer byte is the start of a multi-byte operation, get the
579 	 * next byte, which is either the op code or a control character value.
580 	 */
581 	op = echo_buf(ldata, *tail + 1);
582 
583 	switch (op) {
584 	case ECHO_OP_ERASE_TAB: {
585 		unsigned int num_chars, num_bs;
586 
587 		if (MASK(ldata->echo_commit) == MASK(*tail + 2))
588 			return -ENODATA;
589 
590 		num_chars = echo_buf(ldata, *tail + 2);
591 
592 		/*
593 		 * Determine how many columns to go back in order to erase the
594 		 * tab. This depends on the number of columns used by other
595 		 * characters within the tab area. If this (modulo 8) count is
596 		 * from the start of input rather than from a previous tab, we
597 		 * offset by canon column. Otherwise, tab spacing is normal.
598 		 */
599 		if (!(num_chars & 0x80))
600 			num_chars += ldata->canon_column;
601 		num_bs = 8 - (num_chars & 7);
602 
603 		if (num_bs > space)
604 			return -ENOSPC;
605 
606 		space -= num_bs;
607 		while (num_bs--) {
608 			tty_put_char(tty, '\b');
609 			if (ldata->column > 0)
610 				ldata->column--;
611 		}
612 		*tail += 3;
613 		break;
614 	}
615 	case ECHO_OP_SET_CANON_COL:
616 		ldata->canon_column = ldata->column;
617 		*tail += 2;
618 		break;
619 
620 	case ECHO_OP_MOVE_BACK_COL:
621 		if (ldata->column > 0)
622 			ldata->column--;
623 		*tail += 2;
624 		break;
625 
626 	case ECHO_OP_START:
627 		/* This is an escaped echo op start code */
628 		if (!space)
629 			return -ENOSPC;
630 
631 		tty_put_char(tty, ECHO_OP_START);
632 		ldata->column++;
633 		space--;
634 		*tail += 2;
635 		break;
636 
637 	default:
638 		/*
639 		 * If the op is not a special byte code, it is a ctrl char
640 		 * tagged to be echoed as "^X" (where X is the letter
641 		 * representing the control char). Note that we must ensure
642 		 * there is enough space for the whole ctrl pair.
643 		 */
644 		if (space < 2)
645 			return -ENOSPC;
646 
647 		tty_put_char(tty, '^');
648 		tty_put_char(tty, op ^ 0100);
649 		ldata->column += 2;
650 		space -= 2;
651 		*tail += 2;
652 		break;
653 	}
654 
655 	return space;
656 }
657 
658 /**
659  * __process_echoes	-	write pending echo characters
660  * @tty: terminal device
661  *
662  * Write previously buffered echo (and other ldisc-generated) characters to the
663  * tty.
664  *
665  * Characters generated by the ldisc (including echoes) need to be buffered
666  * because the driver's write buffer can fill during heavy program output.
667  * Echoing straight to the driver will often fail under these conditions,
668  * causing lost characters and resulting mismatches of ldisc state information.
669  *
670  * Since the ldisc state must represent the characters actually sent to the
671  * driver at the time of the write, operations like certain changes in column
672  * state are also saved in the buffer and executed here.
673  *
674  * A circular fifo buffer is used so that the most recent characters are
675  * prioritized. Also, when control characters are echoed with a prefixed "^",
676  * the pair is treated atomically and thus not separated.
677  *
678  * Locking: callers must hold %output_lock.
679  */
__process_echoes(struct tty_struct * tty)680 static size_t __process_echoes(struct tty_struct *tty)
681 {
682 	struct n_tty_data *ldata = tty->disc_data;
683 	unsigned int space, old_space;
684 	size_t tail;
685 	u8 c;
686 
687 	old_space = space = tty_write_room(tty);
688 
689 	tail = ldata->echo_tail;
690 	while (MASK(ldata->echo_commit) != MASK(tail)) {
691 		c = echo_buf(ldata, tail);
692 		if (c == ECHO_OP_START) {
693 			int ret = n_tty_process_echo_ops(tty, &tail, space);
694 			if (ret == -ENODATA)
695 				goto not_yet_stored;
696 			if (ret < 0)
697 				break;
698 			space = ret;
699 		} else {
700 			if (O_OPOST(tty)) {
701 				int retval = do_output_char(c, tty, space);
702 				if (retval < 0)
703 					break;
704 				space -= retval;
705 			} else {
706 				if (!space)
707 					break;
708 				tty_put_char(tty, c);
709 				space -= 1;
710 			}
711 			tail += 1;
712 		}
713 	}
714 
715 	/* If the echo buffer is nearly full (so that the possibility exists
716 	 * of echo overrun before the next commit), then discard enough
717 	 * data at the tail to prevent a subsequent overrun */
718 	while (ldata->echo_commit > tail &&
719 	       ldata->echo_commit - tail >= ECHO_DISCARD_WATERMARK) {
720 		if (echo_buf(ldata, tail) == ECHO_OP_START) {
721 			if (echo_buf(ldata, tail + 1) == ECHO_OP_ERASE_TAB)
722 				tail += 3;
723 			else
724 				tail += 2;
725 		} else
726 			tail++;
727 	}
728 
729  not_yet_stored:
730 	ldata->echo_tail = tail;
731 	return old_space - space;
732 }
733 
commit_echoes(struct tty_struct * tty)734 static void commit_echoes(struct tty_struct *tty)
735 {
736 	struct n_tty_data *ldata = tty->disc_data;
737 	size_t nr, old, echoed;
738 	size_t head;
739 
740 	mutex_lock(&ldata->output_lock);
741 	head = ldata->echo_head;
742 	ldata->echo_mark = head;
743 	old = ldata->echo_commit - ldata->echo_tail;
744 
745 	/* Process committed echoes if the accumulated # of bytes
746 	 * is over the threshold (and try again each time another
747 	 * block is accumulated) */
748 	nr = head - ldata->echo_tail;
749 	if (nr < ECHO_COMMIT_WATERMARK ||
750 	    (nr % ECHO_BLOCK > old % ECHO_BLOCK)) {
751 		mutex_unlock(&ldata->output_lock);
752 		return;
753 	}
754 
755 	ldata->echo_commit = head;
756 	echoed = __process_echoes(tty);
757 	mutex_unlock(&ldata->output_lock);
758 
759 	if (echoed && tty->ops->flush_chars)
760 		tty->ops->flush_chars(tty);
761 }
762 
process_echoes(struct tty_struct * tty)763 static void process_echoes(struct tty_struct *tty)
764 {
765 	struct n_tty_data *ldata = tty->disc_data;
766 	size_t echoed;
767 
768 	if (ldata->echo_mark == ldata->echo_tail)
769 		return;
770 
771 	mutex_lock(&ldata->output_lock);
772 	ldata->echo_commit = ldata->echo_mark;
773 	echoed = __process_echoes(tty);
774 	mutex_unlock(&ldata->output_lock);
775 
776 	if (echoed && tty->ops->flush_chars)
777 		tty->ops->flush_chars(tty);
778 }
779 
780 /* NB: echo_mark and echo_head should be equivalent here */
flush_echoes(struct tty_struct * tty)781 static void flush_echoes(struct tty_struct *tty)
782 {
783 	struct n_tty_data *ldata = tty->disc_data;
784 
785 	if ((!L_ECHO(tty) && !L_ECHONL(tty)) ||
786 	    ldata->echo_commit == ldata->echo_head)
787 		return;
788 
789 	mutex_lock(&ldata->output_lock);
790 	ldata->echo_commit = ldata->echo_head;
791 	__process_echoes(tty);
792 	mutex_unlock(&ldata->output_lock);
793 }
794 
795 /**
796  * add_echo_byte	-	add a byte to the echo buffer
797  * @c: unicode byte to echo
798  * @ldata: n_tty data
799  *
800  * Add a character or operation byte to the echo buffer.
801  */
add_echo_byte(u8 c,struct n_tty_data * ldata)802 static inline void add_echo_byte(u8 c, struct n_tty_data *ldata)
803 {
804 	*echo_buf_addr(ldata, ldata->echo_head) = c;
805 	smp_wmb(); /* Matches smp_rmb() in echo_buf(). */
806 	ldata->echo_head++;
807 }
808 
809 /**
810  * echo_move_back_col	-	add operation to move back a column
811  * @ldata: n_tty data
812  *
813  * Add an operation to the echo buffer to move back one column.
814  */
echo_move_back_col(struct n_tty_data * ldata)815 static void echo_move_back_col(struct n_tty_data *ldata)
816 {
817 	add_echo_byte(ECHO_OP_START, ldata);
818 	add_echo_byte(ECHO_OP_MOVE_BACK_COL, ldata);
819 }
820 
821 /**
822  * echo_set_canon_col	-	add operation to set the canon column
823  * @ldata: n_tty data
824  *
825  * Add an operation to the echo buffer to set the canon column to the current
826  * column.
827  */
echo_set_canon_col(struct n_tty_data * ldata)828 static void echo_set_canon_col(struct n_tty_data *ldata)
829 {
830 	add_echo_byte(ECHO_OP_START, ldata);
831 	add_echo_byte(ECHO_OP_SET_CANON_COL, ldata);
832 }
833 
834 /**
835  * echo_erase_tab	-	add operation to erase a tab
836  * @num_chars: number of character columns already used
837  * @after_tab: true if num_chars starts after a previous tab
838  * @ldata: n_tty data
839  *
840  * Add an operation to the echo buffer to erase a tab.
841  *
842  * Called by the eraser function, which knows how many character columns have
843  * been used since either a previous tab or the start of input. This
844  * information will be used later, along with canon column (if applicable), to
845  * go back the correct number of columns.
846  */
echo_erase_tab(unsigned int num_chars,int after_tab,struct n_tty_data * ldata)847 static void echo_erase_tab(unsigned int num_chars, int after_tab,
848 			   struct n_tty_data *ldata)
849 {
850 	add_echo_byte(ECHO_OP_START, ldata);
851 	add_echo_byte(ECHO_OP_ERASE_TAB, ldata);
852 
853 	/* We only need to know this modulo 8 (tab spacing) */
854 	num_chars &= 7;
855 
856 	/* Set the high bit as a flag if num_chars is after a previous tab */
857 	if (after_tab)
858 		num_chars |= 0x80;
859 
860 	add_echo_byte(num_chars, ldata);
861 }
862 
863 /**
864  * echo_char_raw	-	echo a character raw
865  * @c: unicode byte to echo
866  * @ldata: line disc data
867  *
868  * Echo user input back onto the screen. This must be called only when
869  * L_ECHO(tty) is true. Called from the &tty_driver.receive_buf() path.
870  *
871  * This variant does not treat control characters specially.
872  */
echo_char_raw(u8 c,struct n_tty_data * ldata)873 static void echo_char_raw(u8 c, struct n_tty_data *ldata)
874 {
875 	if (c == ECHO_OP_START) {
876 		add_echo_byte(ECHO_OP_START, ldata);
877 		add_echo_byte(ECHO_OP_START, ldata);
878 	} else {
879 		add_echo_byte(c, ldata);
880 	}
881 }
882 
883 /**
884  * echo_char		-	echo a character
885  * @c: unicode byte to echo
886  * @tty: terminal device
887  *
888  * Echo user input back onto the screen. This must be called only when
889  * L_ECHO(tty) is true. Called from the &tty_driver.receive_buf() path.
890  *
891  * This variant tags control characters to be echoed as "^X" (where X is the
892  * letter representing the control char).
893  */
echo_char(u8 c,const struct tty_struct * tty)894 static void echo_char(u8 c, const struct tty_struct *tty)
895 {
896 	struct n_tty_data *ldata = tty->disc_data;
897 
898 	if (c == ECHO_OP_START) {
899 		add_echo_byte(ECHO_OP_START, ldata);
900 		add_echo_byte(ECHO_OP_START, ldata);
901 	} else {
902 		if (L_ECHOCTL(tty) && iscntrl(c) && c != '\t')
903 			add_echo_byte(ECHO_OP_START, ldata);
904 		add_echo_byte(c, ldata);
905 	}
906 }
907 
908 /**
909  * finish_erasing	-	complete erase
910  * @ldata: n_tty data
911  */
finish_erasing(struct n_tty_data * ldata)912 static inline void finish_erasing(struct n_tty_data *ldata)
913 {
914 	if (ldata->erasing) {
915 		echo_char_raw('/', ldata);
916 		ldata->erasing = 0;
917 	}
918 }
919 
920 /**
921  * eraser		-	handle erase function
922  * @c: character input
923  * @tty: terminal device
924  *
925  * Perform erase and necessary output when an erase character is present in the
926  * stream from the driver layer. Handles the complexities of UTF-8 multibyte
927  * symbols.
928  *
929  * Locking: n_tty_receive_buf()/producer path:
930  *	caller holds non-exclusive %termios_rwsem
931  */
eraser(u8 c,const struct tty_struct * tty)932 static void eraser(u8 c, const struct tty_struct *tty)
933 {
934 	struct n_tty_data *ldata = tty->disc_data;
935 	enum { ERASE, WERASE, KILL } kill_type;
936 	size_t head;
937 	size_t cnt;
938 	int seen_alnums;
939 
940 	if (ldata->read_head == ldata->canon_head) {
941 		/* process_output('\a', tty); */ /* what do you think? */
942 		return;
943 	}
944 	if (c == ERASE_CHAR(tty))
945 		kill_type = ERASE;
946 	else if (c == WERASE_CHAR(tty))
947 		kill_type = WERASE;
948 	else {
949 		if (!L_ECHO(tty)) {
950 			ldata->read_head = ldata->canon_head;
951 			return;
952 		}
953 		if (!L_ECHOK(tty) || !L_ECHOKE(tty) || !L_ECHOE(tty)) {
954 			ldata->read_head = ldata->canon_head;
955 			finish_erasing(ldata);
956 			echo_char(KILL_CHAR(tty), tty);
957 			/* Add a newline if ECHOK is on and ECHOKE is off. */
958 			if (L_ECHOK(tty))
959 				echo_char_raw('\n', ldata);
960 			return;
961 		}
962 		kill_type = KILL;
963 	}
964 
965 	seen_alnums = 0;
966 	while (MASK(ldata->read_head) != MASK(ldata->canon_head)) {
967 		head = ldata->read_head;
968 
969 		/* erase a single possibly multibyte character */
970 		do {
971 			head--;
972 			c = read_buf(ldata, head);
973 		} while (is_continuation(c, tty) &&
974 			 MASK(head) != MASK(ldata->canon_head));
975 
976 		/* do not partially erase */
977 		if (is_continuation(c, tty))
978 			break;
979 
980 		if (kill_type == WERASE) {
981 			/* Equivalent to BSD's ALTWERASE. */
982 			if (isalnum(c) || c == '_')
983 				seen_alnums++;
984 			else if (seen_alnums)
985 				break;
986 		}
987 		cnt = ldata->read_head - head;
988 		ldata->read_head = head;
989 		if (L_ECHO(tty)) {
990 			if (L_ECHOPRT(tty)) {
991 				if (!ldata->erasing) {
992 					echo_char_raw('\\', ldata);
993 					ldata->erasing = 1;
994 				}
995 				/* if cnt > 1, output a multi-byte character */
996 				echo_char(c, tty);
997 				while (--cnt > 0) {
998 					head++;
999 					echo_char_raw(read_buf(ldata, head), ldata);
1000 					echo_move_back_col(ldata);
1001 				}
1002 			} else if (kill_type == ERASE && !L_ECHOE(tty)) {
1003 				echo_char(ERASE_CHAR(tty), tty);
1004 			} else if (c == '\t') {
1005 				unsigned int num_chars = 0;
1006 				int after_tab = 0;
1007 				size_t tail = ldata->read_head;
1008 
1009 				/*
1010 				 * Count the columns used for characters
1011 				 * since the start of input or after a
1012 				 * previous tab.
1013 				 * This info is used to go back the correct
1014 				 * number of columns.
1015 				 */
1016 				while (MASK(tail) != MASK(ldata->canon_head)) {
1017 					tail--;
1018 					c = read_buf(ldata, tail);
1019 					if (c == '\t') {
1020 						after_tab = 1;
1021 						break;
1022 					} else if (iscntrl(c)) {
1023 						if (L_ECHOCTL(tty))
1024 							num_chars += 2;
1025 					} else if (!is_continuation(c, tty)) {
1026 						num_chars++;
1027 					}
1028 				}
1029 				echo_erase_tab(num_chars, after_tab, ldata);
1030 			} else {
1031 				if (iscntrl(c) && L_ECHOCTL(tty)) {
1032 					echo_char_raw('\b', ldata);
1033 					echo_char_raw(' ', ldata);
1034 					echo_char_raw('\b', ldata);
1035 				}
1036 				if (!iscntrl(c) || L_ECHOCTL(tty)) {
1037 					echo_char_raw('\b', ldata);
1038 					echo_char_raw(' ', ldata);
1039 					echo_char_raw('\b', ldata);
1040 				}
1041 			}
1042 		}
1043 		if (kill_type == ERASE)
1044 			break;
1045 	}
1046 	if (ldata->read_head == ldata->canon_head && L_ECHO(tty))
1047 		finish_erasing(ldata);
1048 }
1049 
1050 
__isig(int sig,struct tty_struct * tty)1051 static void __isig(int sig, struct tty_struct *tty)
1052 {
1053 	struct pid *tty_pgrp = tty_get_pgrp(tty);
1054 	if (tty_pgrp) {
1055 		kill_pgrp(tty_pgrp, sig, 1);
1056 		put_pid(tty_pgrp);
1057 	}
1058 }
1059 
1060 /**
1061  * isig			-	handle the ISIG optio
1062  * @sig: signal
1063  * @tty: terminal
1064  *
1065  * Called when a signal is being sent due to terminal input. Called from the
1066  * &tty_driver.receive_buf() path, so serialized.
1067  *
1068  * Performs input and output flush if !NOFLSH. In this context, the echo
1069  * buffer is 'output'. The signal is processed first to alert any current
1070  * readers or writers to discontinue and exit their i/o loops.
1071  *
1072  * Locking: %ctrl.lock
1073  */
isig(int sig,struct tty_struct * tty)1074 static void isig(int sig, struct tty_struct *tty)
1075 {
1076 	struct n_tty_data *ldata = tty->disc_data;
1077 
1078 	if (L_NOFLSH(tty)) {
1079 		/* signal only */
1080 		__isig(sig, tty);
1081 
1082 	} else { /* signal and flush */
1083 		up_read(&tty->termios_rwsem);
1084 		down_write(&tty->termios_rwsem);
1085 
1086 		__isig(sig, tty);
1087 
1088 		/* clear echo buffer */
1089 		mutex_lock(&ldata->output_lock);
1090 		ldata->echo_head = ldata->echo_tail = 0;
1091 		ldata->echo_mark = ldata->echo_commit = 0;
1092 		mutex_unlock(&ldata->output_lock);
1093 
1094 		/* clear output buffer */
1095 		tty_driver_flush_buffer(tty);
1096 
1097 		/* clear input buffer */
1098 		reset_buffer_flags(tty->disc_data);
1099 
1100 		/* notify pty master of flush */
1101 		if (tty->link)
1102 			n_tty_packet_mode_flush(tty);
1103 
1104 		up_write(&tty->termios_rwsem);
1105 		down_read(&tty->termios_rwsem);
1106 	}
1107 }
1108 
1109 /**
1110  * n_tty_receive_break	-	handle break
1111  * @tty: terminal
1112  *
1113  * An RS232 break event has been hit in the incoming bitstream. This can cause
1114  * a variety of events depending upon the termios settings.
1115  *
1116  * Locking: n_tty_receive_buf()/producer path:
1117  *	caller holds non-exclusive termios_rwsem
1118  *
1119  * Note: may get exclusive %termios_rwsem if flushing input buffer
1120  */
n_tty_receive_break(struct tty_struct * tty)1121 static void n_tty_receive_break(struct tty_struct *tty)
1122 {
1123 	struct n_tty_data *ldata = tty->disc_data;
1124 
1125 	if (I_IGNBRK(tty))
1126 		return;
1127 	if (I_BRKINT(tty)) {
1128 		isig(SIGINT, tty);
1129 		return;
1130 	}
1131 	if (I_PARMRK(tty)) {
1132 		put_tty_queue('\377', ldata);
1133 		put_tty_queue('\0', ldata);
1134 	}
1135 	put_tty_queue('\0', ldata);
1136 }
1137 
1138 /**
1139  * n_tty_receive_overrun	-	handle overrun reporting
1140  * @tty: terminal
1141  *
1142  * Data arrived faster than we could process it. While the tty driver has
1143  * flagged this the bits that were missed are gone forever.
1144  *
1145  * Called from the receive_buf path so single threaded. Does not need locking
1146  * as num_overrun and overrun_time are function private.
1147  */
n_tty_receive_overrun(const struct tty_struct * tty)1148 static void n_tty_receive_overrun(const struct tty_struct *tty)
1149 {
1150 	struct n_tty_data *ldata = tty->disc_data;
1151 
1152 	ldata->num_overrun++;
1153 	if (time_is_before_jiffies(ldata->overrun_time + HZ)) {
1154 		tty_warn(tty, "%u input overrun(s)\n", ldata->num_overrun);
1155 		ldata->overrun_time = jiffies;
1156 		ldata->num_overrun = 0;
1157 	}
1158 }
1159 
1160 /**
1161  * n_tty_receive_parity_error	-	error notifier
1162  * @tty: terminal device
1163  * @c: character
1164  *
1165  * Process a parity error and queue the right data to indicate the error case
1166  * if necessary.
1167  *
1168  * Locking: n_tty_receive_buf()/producer path:
1169  * 	caller holds non-exclusive %termios_rwsem
1170  */
n_tty_receive_parity_error(const struct tty_struct * tty,u8 c)1171 static void n_tty_receive_parity_error(const struct tty_struct *tty,
1172 				       u8 c)
1173 {
1174 	struct n_tty_data *ldata = tty->disc_data;
1175 
1176 	if (I_INPCK(tty)) {
1177 		if (I_IGNPAR(tty))
1178 			return;
1179 		if (I_PARMRK(tty)) {
1180 			put_tty_queue('\377', ldata);
1181 			put_tty_queue('\0', ldata);
1182 			put_tty_queue(c, ldata);
1183 		} else
1184 			put_tty_queue('\0', ldata);
1185 	} else
1186 		put_tty_queue(c, ldata);
1187 }
1188 
1189 static void
n_tty_receive_signal_char(struct tty_struct * tty,int signal,u8 c)1190 n_tty_receive_signal_char(struct tty_struct *tty, int signal, u8 c)
1191 {
1192 	isig(signal, tty);
1193 	if (I_IXON(tty))
1194 		start_tty(tty);
1195 	if (L_ECHO(tty)) {
1196 		echo_char(c, tty);
1197 		commit_echoes(tty);
1198 	} else
1199 		process_echoes(tty);
1200 }
1201 
n_tty_is_char_flow_ctrl(struct tty_struct * tty,u8 c)1202 static bool n_tty_is_char_flow_ctrl(struct tty_struct *tty, u8 c)
1203 {
1204 	return c == START_CHAR(tty) || c == STOP_CHAR(tty);
1205 }
1206 
1207 /**
1208  * n_tty_receive_char_flow_ctrl - receive flow control chars
1209  * @tty: terminal device
1210  * @c: character
1211  * @lookahead_done: lookahead has processed this character already
1212  *
1213  * Receive and process flow control character actions.
1214  *
1215  * In case lookahead for flow control chars already handled the character in
1216  * advance to the normal receive, the actions are skipped during normal
1217  * receive.
1218  *
1219  * Returns true if @c is consumed as flow-control character, the character
1220  * must not be treated as normal character.
1221  */
n_tty_receive_char_flow_ctrl(struct tty_struct * tty,u8 c,bool lookahead_done)1222 static bool n_tty_receive_char_flow_ctrl(struct tty_struct *tty, u8 c,
1223 					 bool lookahead_done)
1224 {
1225 	if (!n_tty_is_char_flow_ctrl(tty, c))
1226 		return false;
1227 
1228 	if (lookahead_done)
1229 		return true;
1230 
1231 	if (c == START_CHAR(tty)) {
1232 		start_tty(tty);
1233 		process_echoes(tty);
1234 		return true;
1235 	}
1236 
1237 	/* STOP_CHAR */
1238 	stop_tty(tty);
1239 	return true;
1240 }
1241 
n_tty_receive_handle_newline(struct tty_struct * tty,u8 c)1242 static void n_tty_receive_handle_newline(struct tty_struct *tty, u8 c)
1243 {
1244 	struct n_tty_data *ldata = tty->disc_data;
1245 
1246 	set_bit(MASK(ldata->read_head), ldata->read_flags);
1247 	put_tty_queue(c, ldata);
1248 	smp_store_release(&ldata->canon_head, ldata->read_head);
1249 	kill_fasync(&tty->fasync, SIGIO, POLL_IN);
1250 	wake_up_interruptible_poll(&tty->read_wait, EPOLLIN | EPOLLRDNORM);
1251 }
1252 
n_tty_receive_char_canon(struct tty_struct * tty,u8 c)1253 static bool n_tty_receive_char_canon(struct tty_struct *tty, u8 c)
1254 {
1255 	struct n_tty_data *ldata = tty->disc_data;
1256 
1257 	if (c == ERASE_CHAR(tty) || c == KILL_CHAR(tty) ||
1258 	    (c == WERASE_CHAR(tty) && L_IEXTEN(tty))) {
1259 		eraser(c, tty);
1260 		commit_echoes(tty);
1261 
1262 		return true;
1263 	}
1264 
1265 	if (c == LNEXT_CHAR(tty) && L_IEXTEN(tty)) {
1266 		ldata->lnext = 1;
1267 		if (L_ECHO(tty)) {
1268 			finish_erasing(ldata);
1269 			if (L_ECHOCTL(tty)) {
1270 				echo_char_raw('^', ldata);
1271 				echo_char_raw('\b', ldata);
1272 				commit_echoes(tty);
1273 			}
1274 		}
1275 
1276 		return true;
1277 	}
1278 
1279 	if (c == REPRINT_CHAR(tty) && L_ECHO(tty) && L_IEXTEN(tty)) {
1280 		size_t tail = ldata->canon_head;
1281 
1282 		finish_erasing(ldata);
1283 		echo_char(c, tty);
1284 		echo_char_raw('\n', ldata);
1285 		while (MASK(tail) != MASK(ldata->read_head)) {
1286 			echo_char(read_buf(ldata, tail), tty);
1287 			tail++;
1288 		}
1289 		commit_echoes(tty);
1290 
1291 		return true;
1292 	}
1293 
1294 	if (c == '\n') {
1295 		if (L_ECHO(tty) || L_ECHONL(tty)) {
1296 			echo_char_raw('\n', ldata);
1297 			commit_echoes(tty);
1298 		}
1299 		n_tty_receive_handle_newline(tty, c);
1300 
1301 		return true;
1302 	}
1303 
1304 	if (c == EOF_CHAR(tty)) {
1305 		c = __DISABLED_CHAR;
1306 		n_tty_receive_handle_newline(tty, c);
1307 
1308 		return true;
1309 	}
1310 
1311 	if ((c == EOL_CHAR(tty)) ||
1312 	    (c == EOL2_CHAR(tty) && L_IEXTEN(tty))) {
1313 		/*
1314 		 * XXX are EOL_CHAR and EOL2_CHAR echoed?!?
1315 		 */
1316 		if (L_ECHO(tty)) {
1317 			/* Record the column of first canon char. */
1318 			if (ldata->canon_head == ldata->read_head)
1319 				echo_set_canon_col(ldata);
1320 			echo_char(c, tty);
1321 			commit_echoes(tty);
1322 		}
1323 		/*
1324 		 * XXX does PARMRK doubling happen for
1325 		 * EOL_CHAR and EOL2_CHAR?
1326 		 */
1327 		if (c == '\377' && I_PARMRK(tty))
1328 			put_tty_queue(c, ldata);
1329 
1330 		n_tty_receive_handle_newline(tty, c);
1331 
1332 		return true;
1333 	}
1334 
1335 	return false;
1336 }
1337 
n_tty_receive_char_special(struct tty_struct * tty,u8 c,bool lookahead_done)1338 static void n_tty_receive_char_special(struct tty_struct *tty, u8 c,
1339 				       bool lookahead_done)
1340 {
1341 	struct n_tty_data *ldata = tty->disc_data;
1342 
1343 	if (I_IXON(tty) && n_tty_receive_char_flow_ctrl(tty, c, lookahead_done))
1344 		return;
1345 
1346 	if (L_ISIG(tty)) {
1347 		if (c == INTR_CHAR(tty)) {
1348 			n_tty_receive_signal_char(tty, SIGINT, c);
1349 			return;
1350 		} else if (c == QUIT_CHAR(tty)) {
1351 			n_tty_receive_signal_char(tty, SIGQUIT, c);
1352 			return;
1353 		} else if (c == SUSP_CHAR(tty)) {
1354 			n_tty_receive_signal_char(tty, SIGTSTP, c);
1355 			return;
1356 		}
1357 	}
1358 
1359 	if (tty->flow.stopped && !tty->flow.tco_stopped && I_IXON(tty) && I_IXANY(tty)) {
1360 		start_tty(tty);
1361 		process_echoes(tty);
1362 	}
1363 
1364 	if (c == '\r') {
1365 		if (I_IGNCR(tty))
1366 			return;
1367 		if (I_ICRNL(tty))
1368 			c = '\n';
1369 	} else if (c == '\n' && I_INLCR(tty))
1370 		c = '\r';
1371 
1372 	if (ldata->icanon && n_tty_receive_char_canon(tty, c))
1373 		return;
1374 
1375 	if (L_ECHO(tty)) {
1376 		finish_erasing(ldata);
1377 		if (c == '\n')
1378 			echo_char_raw('\n', ldata);
1379 		else {
1380 			/* Record the column of first canon char. */
1381 			if (ldata->canon_head == ldata->read_head)
1382 				echo_set_canon_col(ldata);
1383 			echo_char(c, tty);
1384 		}
1385 		commit_echoes(tty);
1386 	}
1387 
1388 	/* PARMRK doubling check */
1389 	if (c == '\377' && I_PARMRK(tty))
1390 		put_tty_queue(c, ldata);
1391 
1392 	put_tty_queue(c, ldata);
1393 }
1394 
1395 /**
1396  * n_tty_receive_char	-	perform processing
1397  * @tty: terminal device
1398  * @c: character
1399  *
1400  * Process an individual character of input received from the driver.  This is
1401  * serialized with respect to itself by the rules for the driver above.
1402  *
1403  * Locking: n_tty_receive_buf()/producer path:
1404  *	caller holds non-exclusive %termios_rwsem
1405  *	publishes canon_head if canonical mode is active
1406  */
n_tty_receive_char(struct tty_struct * tty,u8 c)1407 static void n_tty_receive_char(struct tty_struct *tty, u8 c)
1408 {
1409 	struct n_tty_data *ldata = tty->disc_data;
1410 
1411 	if (tty->flow.stopped && !tty->flow.tco_stopped && I_IXON(tty) && I_IXANY(tty)) {
1412 		start_tty(tty);
1413 		process_echoes(tty);
1414 	}
1415 	if (L_ECHO(tty)) {
1416 		finish_erasing(ldata);
1417 		/* Record the column of first canon char. */
1418 		if (ldata->canon_head == ldata->read_head)
1419 			echo_set_canon_col(ldata);
1420 		echo_char(c, tty);
1421 		commit_echoes(tty);
1422 	}
1423 	/* PARMRK doubling check */
1424 	if (c == '\377' && I_PARMRK(tty))
1425 		put_tty_queue(c, ldata);
1426 	put_tty_queue(c, ldata);
1427 }
1428 
n_tty_receive_char_closing(struct tty_struct * tty,u8 c,bool lookahead_done)1429 static void n_tty_receive_char_closing(struct tty_struct *tty, u8 c,
1430 				       bool lookahead_done)
1431 {
1432 	if (I_ISTRIP(tty))
1433 		c &= 0x7f;
1434 	if (I_IUCLC(tty) && L_IEXTEN(tty))
1435 		c = tolower(c);
1436 
1437 	if (I_IXON(tty)) {
1438 		if (!n_tty_receive_char_flow_ctrl(tty, c, lookahead_done) &&
1439 		    tty->flow.stopped && !tty->flow.tco_stopped && I_IXANY(tty) &&
1440 		    c != INTR_CHAR(tty) && c != QUIT_CHAR(tty) &&
1441 		    c != SUSP_CHAR(tty)) {
1442 			start_tty(tty);
1443 			process_echoes(tty);
1444 		}
1445 	}
1446 }
1447 
1448 static void
n_tty_receive_char_flagged(struct tty_struct * tty,u8 c,u8 flag)1449 n_tty_receive_char_flagged(struct tty_struct *tty, u8 c, u8 flag)
1450 {
1451 	switch (flag) {
1452 	case TTY_BREAK:
1453 		n_tty_receive_break(tty);
1454 		break;
1455 	case TTY_PARITY:
1456 	case TTY_FRAME:
1457 		n_tty_receive_parity_error(tty, c);
1458 		break;
1459 	case TTY_OVERRUN:
1460 		n_tty_receive_overrun(tty);
1461 		break;
1462 	default:
1463 		tty_err(tty, "unknown flag %u\n", flag);
1464 		break;
1465 	}
1466 }
1467 
1468 static void
n_tty_receive_char_lnext(struct tty_struct * tty,u8 c,u8 flag)1469 n_tty_receive_char_lnext(struct tty_struct *tty, u8 c, u8 flag)
1470 {
1471 	struct n_tty_data *ldata = tty->disc_data;
1472 
1473 	ldata->lnext = 0;
1474 	if (likely(flag == TTY_NORMAL)) {
1475 		if (I_ISTRIP(tty))
1476 			c &= 0x7f;
1477 		if (I_IUCLC(tty) && L_IEXTEN(tty))
1478 			c = tolower(c);
1479 		n_tty_receive_char(tty, c);
1480 	} else
1481 		n_tty_receive_char_flagged(tty, c, flag);
1482 }
1483 
1484 /* Caller must ensure count > 0 */
n_tty_lookahead_flow_ctrl(struct tty_struct * tty,const u8 * cp,const u8 * fp,size_t count)1485 static void n_tty_lookahead_flow_ctrl(struct tty_struct *tty, const u8 *cp,
1486 				      const u8 *fp, size_t count)
1487 {
1488 	struct n_tty_data *ldata = tty->disc_data;
1489 	u8 flag = TTY_NORMAL;
1490 
1491 	ldata->lookahead_count += count;
1492 
1493 	if (!I_IXON(tty))
1494 		return;
1495 
1496 	while (count--) {
1497 		if (fp)
1498 			flag = *fp++;
1499 		if (likely(flag == TTY_NORMAL))
1500 			n_tty_receive_char_flow_ctrl(tty, *cp, false);
1501 		cp++;
1502 	}
1503 }
1504 
1505 static void
n_tty_receive_buf_real_raw(const struct tty_struct * tty,const u8 * cp,size_t count)1506 n_tty_receive_buf_real_raw(const struct tty_struct *tty, const u8 *cp,
1507 			   size_t count)
1508 {
1509 	struct n_tty_data *ldata = tty->disc_data;
1510 
1511 	/* handle buffer wrap-around by a loop */
1512 	for (unsigned int i = 0; i < 2; i++) {
1513 		size_t head = MASK(ldata->read_head);
1514 		size_t n = min(count, N_TTY_BUF_SIZE - head);
1515 
1516 		memcpy(read_buf_addr(ldata, head), cp, n);
1517 
1518 		ldata->read_head += n;
1519 		cp += n;
1520 		count -= n;
1521 	}
1522 }
1523 
1524 static void
n_tty_receive_buf_raw(struct tty_struct * tty,const u8 * cp,const u8 * fp,size_t count)1525 n_tty_receive_buf_raw(struct tty_struct *tty, const u8 *cp, const u8 *fp,
1526 		      size_t count)
1527 {
1528 	struct n_tty_data *ldata = tty->disc_data;
1529 	u8 flag = TTY_NORMAL;
1530 
1531 	while (count--) {
1532 		if (fp)
1533 			flag = *fp++;
1534 		if (likely(flag == TTY_NORMAL))
1535 			put_tty_queue(*cp++, ldata);
1536 		else
1537 			n_tty_receive_char_flagged(tty, *cp++, flag);
1538 	}
1539 }
1540 
1541 static void
n_tty_receive_buf_closing(struct tty_struct * tty,const u8 * cp,const u8 * fp,size_t count,bool lookahead_done)1542 n_tty_receive_buf_closing(struct tty_struct *tty, const u8 *cp, const u8 *fp,
1543 			  size_t count, bool lookahead_done)
1544 {
1545 	u8 flag = TTY_NORMAL;
1546 
1547 	while (count--) {
1548 		if (fp)
1549 			flag = *fp++;
1550 		if (likely(flag == TTY_NORMAL))
1551 			n_tty_receive_char_closing(tty, *cp++, lookahead_done);
1552 	}
1553 }
1554 
n_tty_receive_buf_standard(struct tty_struct * tty,const u8 * cp,const u8 * fp,size_t count,bool lookahead_done)1555 static void n_tty_receive_buf_standard(struct tty_struct *tty, const u8 *cp,
1556 				       const u8 *fp, size_t count,
1557 				       bool lookahead_done)
1558 {
1559 	struct n_tty_data *ldata = tty->disc_data;
1560 	u8 flag = TTY_NORMAL;
1561 
1562 	while (count--) {
1563 		u8 c = *cp++;
1564 
1565 		if (fp)
1566 			flag = *fp++;
1567 
1568 		if (ldata->lnext) {
1569 			n_tty_receive_char_lnext(tty, c, flag);
1570 			continue;
1571 		}
1572 
1573 		if (unlikely(flag != TTY_NORMAL)) {
1574 			n_tty_receive_char_flagged(tty, c, flag);
1575 			continue;
1576 		}
1577 
1578 		if (I_ISTRIP(tty))
1579 			c &= 0x7f;
1580 		if (I_IUCLC(tty) && L_IEXTEN(tty))
1581 			c = tolower(c);
1582 		if (L_EXTPROC(tty)) {
1583 			put_tty_queue(c, ldata);
1584 			continue;
1585 		}
1586 
1587 		if (test_bit(c, ldata->char_map))
1588 			n_tty_receive_char_special(tty, c, lookahead_done);
1589 		else
1590 			n_tty_receive_char(tty, c);
1591 	}
1592 }
1593 
__receive_buf(struct tty_struct * tty,const u8 * cp,const u8 * fp,size_t count)1594 static void __receive_buf(struct tty_struct *tty, const u8 *cp, const u8 *fp,
1595 			  size_t count)
1596 {
1597 	struct n_tty_data *ldata = tty->disc_data;
1598 	bool preops = I_ISTRIP(tty) || (I_IUCLC(tty) && L_IEXTEN(tty));
1599 	size_t la_count = min(ldata->lookahead_count, count);
1600 
1601 	if (ldata->real_raw)
1602 		n_tty_receive_buf_real_raw(tty, cp, count);
1603 	else if (ldata->raw || (L_EXTPROC(tty) && !preops))
1604 		n_tty_receive_buf_raw(tty, cp, fp, count);
1605 	else if (tty->closing && !L_EXTPROC(tty)) {
1606 		if (la_count > 0) {
1607 			n_tty_receive_buf_closing(tty, cp, fp, la_count, true);
1608 			cp += la_count;
1609 			if (fp)
1610 				fp += la_count;
1611 			count -= la_count;
1612 		}
1613 		if (count > 0)
1614 			n_tty_receive_buf_closing(tty, cp, fp, count, false);
1615 	} else {
1616 		if (la_count > 0) {
1617 			n_tty_receive_buf_standard(tty, cp, fp, la_count, true);
1618 			cp += la_count;
1619 			if (fp)
1620 				fp += la_count;
1621 			count -= la_count;
1622 		}
1623 		if (count > 0)
1624 			n_tty_receive_buf_standard(tty, cp, fp, count, false);
1625 
1626 		flush_echoes(tty);
1627 		if (tty->ops->flush_chars)
1628 			tty->ops->flush_chars(tty);
1629 	}
1630 
1631 	ldata->lookahead_count -= la_count;
1632 
1633 	if (ldata->icanon && !L_EXTPROC(tty))
1634 		return;
1635 
1636 	/* publish read_head to consumer */
1637 	smp_store_release(&ldata->commit_head, ldata->read_head);
1638 
1639 	if (read_cnt(ldata)) {
1640 		kill_fasync(&tty->fasync, SIGIO, POLL_IN);
1641 		wake_up_interruptible_poll(&tty->read_wait, EPOLLIN | EPOLLRDNORM);
1642 	}
1643 }
1644 
1645 /**
1646  * n_tty_receive_buf_common	-	process input
1647  * @tty: device to receive input
1648  * @cp: input chars
1649  * @fp: flags for each char (if %NULL, all chars are %TTY_NORMAL)
1650  * @count: number of input chars in @cp
1651  * @flow: enable flow control
1652  *
1653  * Called by the terminal driver when a block of characters has been received.
1654  * This function must be called from soft contexts not from interrupt context.
1655  * The driver is responsible for making calls one at a time and in order (or
1656  * using flush_to_ldisc()).
1657  *
1658  * Returns: the # of input chars from @cp which were processed.
1659  *
1660  * In canonical mode, the maximum line length is 4096 chars (including the line
1661  * termination char); lines longer than 4096 chars are truncated. After 4095
1662  * chars, input data is still processed but not stored. Overflow processing
1663  * ensures the tty can always receive more input until at least one line can be
1664  * read.
1665  *
1666  * In non-canonical mode, the read buffer will only accept 4095 chars; this
1667  * provides the necessary space for a newline char if the input mode is
1668  * switched to canonical.
1669  *
1670  * Note it is possible for the read buffer to _contain_ 4096 chars in
1671  * non-canonical mode: the read buffer could already contain the maximum canon
1672  * line of 4096 chars when the mode is switched to non-canonical.
1673  *
1674  * Locking: n_tty_receive_buf()/producer path:
1675  *	claims non-exclusive %termios_rwsem
1676  *	publishes commit_head or canon_head
1677  */
1678 static size_t
n_tty_receive_buf_common(struct tty_struct * tty,const u8 * cp,const u8 * fp,size_t count,bool flow)1679 n_tty_receive_buf_common(struct tty_struct *tty, const u8 *cp, const u8 *fp,
1680 			 size_t count, bool flow)
1681 {
1682 	struct n_tty_data *ldata = tty->disc_data;
1683 	size_t n, rcvd = 0;
1684 	int room, overflow;
1685 
1686 	down_read(&tty->termios_rwsem);
1687 
1688 	do {
1689 		/*
1690 		 * When PARMRK is set, each input char may take up to 3 chars
1691 		 * in the read buf; reduce the buffer space avail by 3x
1692 		 *
1693 		 * If we are doing input canonicalization, and there are no
1694 		 * pending newlines, let characters through without limit, so
1695 		 * that erase characters will be handled.  Other excess
1696 		 * characters will be beeped.
1697 		 *
1698 		 * paired with store in *_copy_from_read_buf() -- guarantees
1699 		 * the consumer has loaded the data in read_buf up to the new
1700 		 * read_tail (so this producer will not overwrite unread data)
1701 		 */
1702 		size_t tail = smp_load_acquire(&ldata->read_tail);
1703 
1704 		room = N_TTY_BUF_SIZE - (ldata->read_head - tail);
1705 		if (I_PARMRK(tty))
1706 			room = DIV_ROUND_UP(room, 3);
1707 		room--;
1708 		if (room <= 0) {
1709 			overflow = ldata->icanon && ldata->canon_head == tail;
1710 			if (overflow && room < 0)
1711 				ldata->read_head--;
1712 			room = overflow;
1713 			WRITE_ONCE(ldata->no_room, flow && !room);
1714 		} else
1715 			overflow = 0;
1716 
1717 		n = min_t(size_t, count, room);
1718 		if (!n)
1719 			break;
1720 
1721 		/* ignore parity errors if handling overflow */
1722 		if (!overflow || !fp || *fp != TTY_PARITY)
1723 			__receive_buf(tty, cp, fp, n);
1724 
1725 		cp += n;
1726 		if (fp)
1727 			fp += n;
1728 		count -= n;
1729 		rcvd += n;
1730 	} while (!test_bit(TTY_LDISC_CHANGING, &tty->flags));
1731 
1732 	tty->receive_room = room;
1733 
1734 	/* Unthrottle if handling overflow on pty */
1735 	if (tty->driver->type == TTY_DRIVER_TYPE_PTY) {
1736 		if (overflow) {
1737 			tty_set_flow_change(tty, TTY_UNTHROTTLE_SAFE);
1738 			tty_unthrottle_safe(tty);
1739 			__tty_set_flow_change(tty, 0);
1740 		}
1741 	} else
1742 		n_tty_check_throttle(tty);
1743 
1744 	if (unlikely(ldata->no_room)) {
1745 		/*
1746 		 * Barrier here is to ensure to read the latest read_tail in
1747 		 * chars_in_buffer() and to make sure that read_tail is not loaded
1748 		 * before ldata->no_room is set.
1749 		 */
1750 		smp_mb();
1751 		if (!chars_in_buffer(tty))
1752 			n_tty_kick_worker(tty);
1753 	}
1754 
1755 	up_read(&tty->termios_rwsem);
1756 
1757 	return rcvd;
1758 }
1759 
n_tty_receive_buf(struct tty_struct * tty,const u8 * cp,const u8 * fp,size_t count)1760 static void n_tty_receive_buf(struct tty_struct *tty, const u8 *cp,
1761 			      const u8 *fp, size_t count)
1762 {
1763 	n_tty_receive_buf_common(tty, cp, fp, count, false);
1764 }
1765 
n_tty_receive_buf2(struct tty_struct * tty,const u8 * cp,const u8 * fp,size_t count)1766 static size_t n_tty_receive_buf2(struct tty_struct *tty, const u8 *cp,
1767 				 const u8 *fp, size_t count)
1768 {
1769 	return n_tty_receive_buf_common(tty, cp, fp, count, true);
1770 }
1771 
1772 /**
1773  * n_tty_set_termios	-	termios data changed
1774  * @tty: terminal
1775  * @old: previous data
1776  *
1777  * Called by the tty layer when the user changes termios flags so that the line
1778  * discipline can plan ahead. This function cannot sleep and is protected from
1779  * re-entry by the tty layer. The user is guaranteed that this function will
1780  * not be re-entered or in progress when the ldisc is closed.
1781  *
1782  * Locking: Caller holds @tty->termios_rwsem
1783  */
n_tty_set_termios(struct tty_struct * tty,const struct ktermios * old)1784 static void n_tty_set_termios(struct tty_struct *tty, const struct ktermios *old)
1785 {
1786 	struct n_tty_data *ldata = tty->disc_data;
1787 
1788 	if (!old || (old->c_lflag ^ tty->termios.c_lflag) & (ICANON | EXTPROC)) {
1789 		bitmap_zero(ldata->read_flags, N_TTY_BUF_SIZE);
1790 		ldata->line_start = ldata->read_tail;
1791 		if (!L_ICANON(tty) || !read_cnt(ldata)) {
1792 			ldata->canon_head = ldata->read_tail;
1793 			ldata->push = 0;
1794 		} else {
1795 			set_bit(MASK(ldata->read_head - 1), ldata->read_flags);
1796 			ldata->canon_head = ldata->read_head;
1797 			ldata->push = 1;
1798 		}
1799 		ldata->commit_head = ldata->read_head;
1800 		ldata->erasing = 0;
1801 		ldata->lnext = 0;
1802 	}
1803 
1804 	ldata->icanon = (L_ICANON(tty) != 0);
1805 
1806 	if (I_ISTRIP(tty) || I_IUCLC(tty) || I_IGNCR(tty) ||
1807 	    I_ICRNL(tty) || I_INLCR(tty) || L_ICANON(tty) ||
1808 	    I_IXON(tty) || L_ISIG(tty) || L_ECHO(tty) ||
1809 	    I_PARMRK(tty)) {
1810 		bitmap_zero(ldata->char_map, 256);
1811 
1812 		if (I_IGNCR(tty) || I_ICRNL(tty))
1813 			set_bit('\r', ldata->char_map);
1814 		if (I_INLCR(tty))
1815 			set_bit('\n', ldata->char_map);
1816 
1817 		if (L_ICANON(tty)) {
1818 			set_bit(ERASE_CHAR(tty), ldata->char_map);
1819 			set_bit(KILL_CHAR(tty), ldata->char_map);
1820 			set_bit(EOF_CHAR(tty), ldata->char_map);
1821 			set_bit('\n', ldata->char_map);
1822 			set_bit(EOL_CHAR(tty), ldata->char_map);
1823 			if (L_IEXTEN(tty)) {
1824 				set_bit(WERASE_CHAR(tty), ldata->char_map);
1825 				set_bit(LNEXT_CHAR(tty), ldata->char_map);
1826 				set_bit(EOL2_CHAR(tty), ldata->char_map);
1827 				if (L_ECHO(tty))
1828 					set_bit(REPRINT_CHAR(tty),
1829 						ldata->char_map);
1830 			}
1831 		}
1832 		if (I_IXON(tty)) {
1833 			set_bit(START_CHAR(tty), ldata->char_map);
1834 			set_bit(STOP_CHAR(tty), ldata->char_map);
1835 		}
1836 		if (L_ISIG(tty)) {
1837 			set_bit(INTR_CHAR(tty), ldata->char_map);
1838 			set_bit(QUIT_CHAR(tty), ldata->char_map);
1839 			set_bit(SUSP_CHAR(tty), ldata->char_map);
1840 		}
1841 		clear_bit(__DISABLED_CHAR, ldata->char_map);
1842 		ldata->raw = 0;
1843 		ldata->real_raw = 0;
1844 	} else {
1845 		ldata->raw = 1;
1846 		if ((I_IGNBRK(tty) || (!I_BRKINT(tty) && !I_PARMRK(tty))) &&
1847 		    (I_IGNPAR(tty) || !I_INPCK(tty)) &&
1848 		    (tty->driver->flags & TTY_DRIVER_REAL_RAW))
1849 			ldata->real_raw = 1;
1850 		else
1851 			ldata->real_raw = 0;
1852 	}
1853 	/*
1854 	 * Fix tty hang when I_IXON(tty) is cleared, but the tty
1855 	 * been stopped by STOP_CHAR(tty) before it.
1856 	 */
1857 	if (!I_IXON(tty) && old && (old->c_iflag & IXON) && !tty->flow.tco_stopped) {
1858 		start_tty(tty);
1859 		process_echoes(tty);
1860 	}
1861 
1862 	/* The termios change make the tty ready for I/O */
1863 	wake_up_interruptible(&tty->write_wait);
1864 	wake_up_interruptible(&tty->read_wait);
1865 }
1866 
1867 /**
1868  * n_tty_close		-	close the ldisc for this tty
1869  * @tty: device
1870  *
1871  * Called from the terminal layer when this line discipline is being shut down,
1872  * either because of a close or becsuse of a discipline change. The function
1873  * will not be called while other ldisc methods are in progress.
1874  */
n_tty_close(struct tty_struct * tty)1875 static void n_tty_close(struct tty_struct *tty)
1876 {
1877 	struct n_tty_data *ldata = tty->disc_data;
1878 
1879 	if (tty->link)
1880 		n_tty_packet_mode_flush(tty);
1881 
1882 	down_write(&tty->termios_rwsem);
1883 	vfree(ldata);
1884 	tty->disc_data = NULL;
1885 	up_write(&tty->termios_rwsem);
1886 }
1887 
1888 /**
1889  * n_tty_open		-	open an ldisc
1890  * @tty: terminal to open
1891  *
1892  * Called when this line discipline is being attached to the terminal device.
1893  * Can sleep. Called serialized so that no other events will occur in parallel.
1894  * No further open will occur until a close.
1895  */
n_tty_open(struct tty_struct * tty)1896 static int n_tty_open(struct tty_struct *tty)
1897 {
1898 	struct n_tty_data *ldata;
1899 
1900 	/* Currently a malloc failure here can panic */
1901 	ldata = vzalloc(sizeof(*ldata));
1902 	if (!ldata)
1903 		return -ENOMEM;
1904 
1905 	ldata->overrun_time = jiffies;
1906 	mutex_init(&ldata->atomic_read_lock);
1907 	mutex_init(&ldata->output_lock);
1908 
1909 	tty->disc_data = ldata;
1910 	tty->closing = 0;
1911 	/* indicate buffer work may resume */
1912 	clear_bit(TTY_LDISC_HALTED, &tty->flags);
1913 	n_tty_set_termios(tty, NULL);
1914 	tty_unthrottle(tty);
1915 	return 0;
1916 }
1917 
input_available_p(const struct tty_struct * tty,int poll)1918 static inline int input_available_p(const struct tty_struct *tty, int poll)
1919 {
1920 	const struct n_tty_data *ldata = tty->disc_data;
1921 	int amt = poll && !TIME_CHAR(tty) && MIN_CHAR(tty) ? MIN_CHAR(tty) : 1;
1922 
1923 	if (ldata->icanon && !L_EXTPROC(tty))
1924 		return ldata->canon_head != ldata->read_tail;
1925 	else
1926 		return ldata->commit_head - ldata->read_tail >= amt;
1927 }
1928 
1929 /**
1930  * copy_from_read_buf	-	copy read data directly
1931  * @tty: terminal device
1932  * @kbp: data
1933  * @nr: size of data
1934  *
1935  * Helper function to speed up n_tty_read(). It is only called when %ICANON is
1936  * off; it copies characters straight from the tty queue.
1937  *
1938  * Returns: true if it successfully copied data, but there is still more data
1939  * to be had.
1940  *
1941  * Locking:
1942  *  * called under the @ldata->atomic_read_lock sem
1943  *  * n_tty_read()/consumer path:
1944  *		caller holds non-exclusive %termios_rwsem;
1945  *		read_tail published
1946  */
copy_from_read_buf(const struct tty_struct * tty,u8 ** kbp,size_t * nr)1947 static bool copy_from_read_buf(const struct tty_struct *tty, u8 **kbp,
1948 			       size_t *nr)
1949 
1950 {
1951 	struct n_tty_data *ldata = tty->disc_data;
1952 	size_t n;
1953 	bool is_eof;
1954 	size_t head = smp_load_acquire(&ldata->commit_head);
1955 	size_t tail = MASK(ldata->read_tail);
1956 
1957 	n = min3(head - ldata->read_tail, N_TTY_BUF_SIZE - tail, *nr);
1958 	if (!n)
1959 		return false;
1960 
1961 	u8 *from = read_buf_addr(ldata, tail);
1962 	memcpy(*kbp, from, n);
1963 	is_eof = n == 1 && *from == EOF_CHAR(tty);
1964 	tty_audit_add_data(tty, from, n);
1965 	zero_buffer(tty, from, n);
1966 	smp_store_release(&ldata->read_tail, ldata->read_tail + n);
1967 
1968 	/* Turn single EOF into zero-length read */
1969 	if (L_EXTPROC(tty) && ldata->icanon && is_eof &&
1970 	    head == ldata->read_tail)
1971 		return false;
1972 
1973 	*kbp += n;
1974 	*nr -= n;
1975 
1976 	/* If we have more to copy, let the caller know */
1977 	return head != ldata->read_tail;
1978 }
1979 
1980 /**
1981  * canon_copy_from_read_buf	-	copy read data in canonical mode
1982  * @tty: terminal device
1983  * @kbp: data
1984  * @nr: size of data
1985  *
1986  * Helper function for n_tty_read(). It is only called when %ICANON is on; it
1987  * copies one line of input up to and including the line-delimiting character
1988  * into the result buffer.
1989  *
1990  * Note: When termios is changed from non-canonical to canonical mode and the
1991  * read buffer contains data, n_tty_set_termios() simulates an EOF push (as if
1992  * C-d were input) _without_ the %DISABLED_CHAR in the buffer. This causes data
1993  * already processed as input to be immediately available as input although a
1994  * newline has not been received.
1995  *
1996  * Locking:
1997  *  * called under the %atomic_read_lock mutex
1998  *  * n_tty_read()/consumer path:
1999  *	caller holds non-exclusive %termios_rwsem;
2000  *	read_tail published
2001  */
canon_copy_from_read_buf(const struct tty_struct * tty,u8 ** kbp,size_t * nr)2002 static bool canon_copy_from_read_buf(const struct tty_struct *tty, u8 **kbp,
2003 				     size_t *nr)
2004 {
2005 	struct n_tty_data *ldata = tty->disc_data;
2006 	size_t n, size, more, c;
2007 	size_t eol;
2008 	size_t tail, canon_head;
2009 	int found = 0;
2010 
2011 	/* N.B. avoid overrun if nr == 0 */
2012 	if (!*nr)
2013 		return false;
2014 
2015 	canon_head = smp_load_acquire(&ldata->canon_head);
2016 	n = min(*nr, canon_head - ldata->read_tail);
2017 
2018 	tail = MASK(ldata->read_tail);
2019 	size = min_t(size_t, tail + n, N_TTY_BUF_SIZE);
2020 
2021 	eol = find_next_bit(ldata->read_flags, size, tail);
2022 	more = n - (size - tail);
2023 	if (eol == N_TTY_BUF_SIZE && more) {
2024 		/* scan wrapped without finding set bit */
2025 		eol = find_first_bit(ldata->read_flags, more);
2026 		found = eol != more;
2027 	} else
2028 		found = eol != size;
2029 
2030 	n = eol - tail;
2031 	if (n > N_TTY_BUF_SIZE)
2032 		n += N_TTY_BUF_SIZE;
2033 	c = n + found;
2034 
2035 	if (!found || read_buf(ldata, eol) != __DISABLED_CHAR)
2036 		n = c;
2037 
2038 	tty_copy(tty, *kbp, tail, n);
2039 	*kbp += n;
2040 	*nr -= n;
2041 
2042 	if (found)
2043 		clear_bit(eol, ldata->read_flags);
2044 	smp_store_release(&ldata->read_tail, ldata->read_tail + c);
2045 
2046 	if (found) {
2047 		if (!ldata->push)
2048 			ldata->line_start = ldata->read_tail;
2049 		else
2050 			ldata->push = 0;
2051 		tty_audit_push();
2052 		return false;
2053 	}
2054 
2055 	/* No EOL found - do a continuation retry if there is more data */
2056 	return ldata->read_tail != canon_head;
2057 }
2058 
2059 /*
2060  * If we finished a read at the exact location of an
2061  * EOF (special EOL character that's a __DISABLED_CHAR)
2062  * in the stream, silently eat the EOF.
2063  */
canon_skip_eof(struct n_tty_data * ldata)2064 static void canon_skip_eof(struct n_tty_data *ldata)
2065 {
2066 	size_t tail, canon_head;
2067 
2068 	canon_head = smp_load_acquire(&ldata->canon_head);
2069 	tail = ldata->read_tail;
2070 
2071 	// No data?
2072 	if (tail == canon_head)
2073 		return;
2074 
2075 	// See if the tail position is EOF in the circular buffer
2076 	tail &= (N_TTY_BUF_SIZE - 1);
2077 	if (!test_bit(tail, ldata->read_flags))
2078 		return;
2079 	if (read_buf(ldata, tail) != __DISABLED_CHAR)
2080 		return;
2081 
2082 	// Clear the EOL bit, skip the EOF char.
2083 	clear_bit(tail, ldata->read_flags);
2084 	smp_store_release(&ldata->read_tail, ldata->read_tail + 1);
2085 }
2086 
2087 /**
2088  * job_control		-	check job control
2089  * @tty: tty
2090  * @file: file handle
2091  *
2092  * Perform job control management checks on this @file/@tty descriptor and if
2093  * appropriate send any needed signals and return a negative error code if
2094  * action should be taken.
2095  *
2096  * Locking:
2097  *  * redirected write test is safe
2098  *  * current->signal->tty check is safe
2099  *  * ctrl.lock to safely reference @tty->ctrl.pgrp
2100  */
job_control(struct tty_struct * tty,struct file * file)2101 static int job_control(struct tty_struct *tty, struct file *file)
2102 {
2103 	/* Job control check -- must be done at start and after
2104 	   every sleep (POSIX.1 7.1.1.4). */
2105 	/* NOTE: not yet done after every sleep pending a thorough
2106 	   check of the logic of this change. -- jlc */
2107 	/* don't stop on /dev/console */
2108 	if (file->f_op->write_iter == redirected_tty_write)
2109 		return 0;
2110 
2111 	return __tty_check_change(tty, SIGTTIN);
2112 }
2113 
2114 /*
2115  * We still hold the atomic_read_lock and the termios_rwsem, and can just
2116  * continue to copy data.
2117  */
n_tty_continue_cookie(struct tty_struct * tty,u8 * kbuf,size_t nr,void ** cookie)2118 static ssize_t n_tty_continue_cookie(struct tty_struct *tty, u8 *kbuf,
2119 				   size_t nr, void **cookie)
2120 {
2121 	struct n_tty_data *ldata = tty->disc_data;
2122 	u8 *kb = kbuf;
2123 
2124 	if (ldata->icanon && !L_EXTPROC(tty)) {
2125 		/*
2126 		 * If we have filled the user buffer, see if we should skip an
2127 		 * EOF character before releasing the lock and returning done.
2128 		 */
2129 		if (!nr)
2130 			canon_skip_eof(ldata);
2131 		else if (canon_copy_from_read_buf(tty, &kb, &nr))
2132 			return kb - kbuf;
2133 	} else {
2134 		if (copy_from_read_buf(tty, &kb, &nr))
2135 			return kb - kbuf;
2136 	}
2137 
2138 	/* No more data - release locks and stop retries */
2139 	n_tty_kick_worker(tty);
2140 	n_tty_check_unthrottle(tty);
2141 	up_read(&tty->termios_rwsem);
2142 	mutex_unlock(&ldata->atomic_read_lock);
2143 	*cookie = NULL;
2144 
2145 	return kb - kbuf;
2146 }
2147 
n_tty_wait_for_input(struct tty_struct * tty,struct file * file,struct wait_queue_entry * wait,long * timeout)2148 static int n_tty_wait_for_input(struct tty_struct *tty, struct file *file,
2149 				struct wait_queue_entry *wait, long *timeout)
2150 {
2151 	if (test_bit(TTY_OTHER_CLOSED, &tty->flags))
2152 		return -EIO;
2153 	if (tty_hung_up_p(file))
2154 		return 0;
2155 	/*
2156 	 * Abort readers for ttys which never actually get hung up.
2157 	 * See __tty_hangup().
2158 	 */
2159 	if (test_bit(TTY_HUPPING, &tty->flags))
2160 		return 0;
2161 	if (!*timeout)
2162 		return 0;
2163 	if (tty_io_nonblock(tty, file))
2164 		return -EAGAIN;
2165 	if (signal_pending(current))
2166 		return -ERESTARTSYS;
2167 
2168 	up_read(&tty->termios_rwsem);
2169 	*timeout = wait_woken(wait, TASK_INTERRUPTIBLE, *timeout);
2170 	down_read(&tty->termios_rwsem);
2171 
2172 	return 1;
2173 }
2174 
2175 /**
2176  * n_tty_read		-	read function for tty
2177  * @tty: tty device
2178  * @file: file object
2179  * @kbuf: kernelspace buffer pointer
2180  * @nr: size of I/O
2181  * @cookie: if non-%NULL, this is a continuation read
2182  * @offset: where to continue reading from (unused in n_tty)
2183  *
2184  * Perform reads for the line discipline. We are guaranteed that the line
2185  * discipline will not be closed under us but we may get multiple parallel
2186  * readers and must handle this ourselves. We may also get a hangup. Always
2187  * called in user context, may sleep.
2188  *
2189  * This code must be sure never to sleep through a hangup.
2190  *
2191  * Locking: n_tty_read()/consumer path:
2192  *	claims non-exclusive termios_rwsem;
2193  *	publishes read_tail
2194  */
n_tty_read(struct tty_struct * tty,struct file * file,u8 * kbuf,size_t nr,void ** cookie,unsigned long offset)2195 static ssize_t n_tty_read(struct tty_struct *tty, struct file *file, u8 *kbuf,
2196 			  size_t nr, void **cookie, unsigned long offset)
2197 {
2198 	struct n_tty_data *ldata = tty->disc_data;
2199 	u8 *kb = kbuf;
2200 	DEFINE_WAIT_FUNC(wait, woken_wake_function);
2201 	int minimum, time;
2202 	ssize_t retval;
2203 	long timeout;
2204 	bool packet;
2205 	size_t old_tail;
2206 
2207 	/* Is this a continuation of a read started earlier? */
2208 	if (*cookie)
2209 		return n_tty_continue_cookie(tty, kbuf, nr, cookie);
2210 
2211 	retval = job_control(tty, file);
2212 	if (retval < 0)
2213 		return retval;
2214 
2215 	/*
2216 	 *	Internal serialization of reads.
2217 	 */
2218 	if (file->f_flags & O_NONBLOCK) {
2219 		if (!mutex_trylock(&ldata->atomic_read_lock))
2220 			return -EAGAIN;
2221 	} else {
2222 		if (mutex_lock_interruptible(&ldata->atomic_read_lock))
2223 			return -ERESTARTSYS;
2224 	}
2225 
2226 	down_read(&tty->termios_rwsem);
2227 
2228 	minimum = time = 0;
2229 	timeout = MAX_SCHEDULE_TIMEOUT;
2230 	if (!ldata->icanon) {
2231 		minimum = MIN_CHAR(tty);
2232 		if (minimum) {
2233 			time = (HZ / 10) * TIME_CHAR(tty);
2234 		} else {
2235 			timeout = (HZ / 10) * TIME_CHAR(tty);
2236 			minimum = 1;
2237 		}
2238 	}
2239 
2240 	packet = tty->ctrl.packet;
2241 	old_tail = ldata->read_tail;
2242 
2243 	add_wait_queue(&tty->read_wait, &wait);
2244 	while (nr) {
2245 		/* First test for status change. */
2246 		if (packet && tty->link->ctrl.pktstatus) {
2247 			u8 cs;
2248 			if (kb != kbuf)
2249 				break;
2250 			spin_lock_irq(&tty->link->ctrl.lock);
2251 			cs = tty->link->ctrl.pktstatus;
2252 			tty->link->ctrl.pktstatus = 0;
2253 			spin_unlock_irq(&tty->link->ctrl.lock);
2254 			*kb++ = cs;
2255 			nr--;
2256 			break;
2257 		}
2258 
2259 		if (!input_available_p(tty, 0)) {
2260 			up_read(&tty->termios_rwsem);
2261 			tty_buffer_flush_work(tty->port);
2262 			down_read(&tty->termios_rwsem);
2263 			if (!input_available_p(tty, 0)) {
2264 				int ret = n_tty_wait_for_input(tty, file, &wait,
2265 							       &timeout);
2266 				if (ret <= 0) {
2267 					retval = ret;
2268 					break;
2269 				}
2270 				continue;
2271 			}
2272 		}
2273 
2274 		if (ldata->icanon && !L_EXTPROC(tty)) {
2275 			if (canon_copy_from_read_buf(tty, &kb, &nr))
2276 				goto more_to_be_read;
2277 		} else {
2278 			/* Deal with packet mode. */
2279 			if (packet && kb == kbuf) {
2280 				*kb++ = TIOCPKT_DATA;
2281 				nr--;
2282 			}
2283 
2284 			if (copy_from_read_buf(tty, &kb, &nr) && kb - kbuf >= minimum)
2285 				goto more_to_be_read;
2286 		}
2287 
2288 		n_tty_check_unthrottle(tty);
2289 
2290 		if (kb - kbuf >= minimum)
2291 			break;
2292 		if (time)
2293 			timeout = time;
2294 	}
2295 	if (old_tail != ldata->read_tail) {
2296 		/*
2297 		 * Make sure no_room is not read in n_tty_kick_worker()
2298 		 * before setting ldata->read_tail in copy_from_read_buf().
2299 		 */
2300 		smp_mb();
2301 		n_tty_kick_worker(tty);
2302 	}
2303 	up_read(&tty->termios_rwsem);
2304 
2305 	remove_wait_queue(&tty->read_wait, &wait);
2306 	mutex_unlock(&ldata->atomic_read_lock);
2307 
2308 	if (kb - kbuf)
2309 		retval = kb - kbuf;
2310 
2311 	return retval;
2312 more_to_be_read:
2313 	/*
2314 	 * There is more to be had and we have nothing more to wait for, so
2315 	 * let's mark us for retries.
2316 	 *
2317 	 * NOTE! We return here with both the termios_sem and atomic_read_lock
2318 	 * still held, the retries will release them when done.
2319 	 */
2320 	remove_wait_queue(&tty->read_wait, &wait);
2321 	*cookie = cookie;
2322 
2323 	return kb - kbuf;
2324 }
2325 
2326 /**
2327  * n_tty_write		-	write function for tty
2328  * @tty: tty device
2329  * @file: file object
2330  * @buf: userspace buffer pointer
2331  * @nr: size of I/O
2332  *
2333  * Write function of the terminal device. This is serialized with respect to
2334  * other write callers but not to termios changes, reads and other such events.
2335  * Since the receive code will echo characters, thus calling driver write
2336  * methods, the %output_lock is used in the output processing functions called
2337  * here as well as in the echo processing function to protect the column state
2338  * and space left in the buffer.
2339  *
2340  * This code must be sure never to sleep through a hangup.
2341  *
2342  * Locking: output_lock to protect column state and space left
2343  *	 (note that the process_output*() functions take this lock themselves)
2344  */
2345 
n_tty_write(struct tty_struct * tty,struct file * file,const u8 * buf,size_t nr)2346 static ssize_t n_tty_write(struct tty_struct *tty, struct file *file,
2347 			   const u8 *buf, size_t nr)
2348 {
2349 	const u8 *b = buf;
2350 	DEFINE_WAIT_FUNC(wait, woken_wake_function);
2351 	ssize_t num, retval = 0;
2352 
2353 	/* Job control check -- must be done at start (POSIX.1 7.1.1.4). */
2354 	if (L_TOSTOP(tty) && file->f_op->write_iter != redirected_tty_write) {
2355 		retval = tty_check_change(tty);
2356 		if (retval)
2357 			return retval;
2358 	}
2359 
2360 	down_read(&tty->termios_rwsem);
2361 
2362 	/* Write out any echoed characters that are still pending */
2363 	process_echoes(tty);
2364 
2365 	add_wait_queue(&tty->write_wait, &wait);
2366 	while (1) {
2367 		if (signal_pending(current)) {
2368 			retval = -ERESTARTSYS;
2369 			break;
2370 		}
2371 		if (tty_hung_up_p(file) || (tty->link && !tty->link->count)) {
2372 			retval = -EIO;
2373 			break;
2374 		}
2375 		if (O_OPOST(tty)) {
2376 			while (nr > 0) {
2377 				num = process_output_block(tty, b, nr);
2378 				if (num < 0) {
2379 					if (num == -EAGAIN)
2380 						break;
2381 					retval = num;
2382 					goto break_out;
2383 				}
2384 				b += num;
2385 				nr -= num;
2386 				if (nr == 0)
2387 					break;
2388 				if (process_output(*b, tty) < 0)
2389 					break;
2390 				b++; nr--;
2391 			}
2392 			if (tty->ops->flush_chars)
2393 				tty->ops->flush_chars(tty);
2394 		} else {
2395 			struct n_tty_data *ldata = tty->disc_data;
2396 
2397 			while (nr > 0) {
2398 				mutex_lock(&ldata->output_lock);
2399 				num = tty->ops->write(tty, b, nr);
2400 				mutex_unlock(&ldata->output_lock);
2401 				if (num < 0) {
2402 					retval = num;
2403 					goto break_out;
2404 				}
2405 				if (!num)
2406 					break;
2407 				b += num;
2408 				nr -= num;
2409 			}
2410 		}
2411 		if (!nr)
2412 			break;
2413 		if (tty_io_nonblock(tty, file)) {
2414 			retval = -EAGAIN;
2415 			break;
2416 		}
2417 		up_read(&tty->termios_rwsem);
2418 
2419 		wait_woken(&wait, TASK_INTERRUPTIBLE, MAX_SCHEDULE_TIMEOUT);
2420 
2421 		down_read(&tty->termios_rwsem);
2422 	}
2423 break_out:
2424 	remove_wait_queue(&tty->write_wait, &wait);
2425 	if (nr && tty->fasync)
2426 		set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
2427 	up_read(&tty->termios_rwsem);
2428 	return (b - buf) ? b - buf : retval;
2429 }
2430 
2431 /**
2432  * n_tty_poll		-	poll method for N_TTY
2433  * @tty: terminal device
2434  * @file: file accessing it
2435  * @wait: poll table
2436  *
2437  * Called when the line discipline is asked to poll() for data or for special
2438  * events. This code is not serialized with respect to other events save
2439  * open/close.
2440  *
2441  * This code must be sure never to sleep through a hangup.
2442  *
2443  * Locking: called without the kernel lock held -- fine.
2444  */
n_tty_poll(struct tty_struct * tty,struct file * file,poll_table * wait)2445 static __poll_t n_tty_poll(struct tty_struct *tty, struct file *file,
2446 							poll_table *wait)
2447 {
2448 	__poll_t mask = 0;
2449 
2450 	poll_wait(file, &tty->read_wait, wait);
2451 	poll_wait(file, &tty->write_wait, wait);
2452 	if (input_available_p(tty, 1))
2453 		mask |= EPOLLIN | EPOLLRDNORM;
2454 	else {
2455 		tty_buffer_flush_work(tty->port);
2456 		if (input_available_p(tty, 1))
2457 			mask |= EPOLLIN | EPOLLRDNORM;
2458 	}
2459 	if (tty->ctrl.packet && tty->link->ctrl.pktstatus)
2460 		mask |= EPOLLPRI | EPOLLIN | EPOLLRDNORM;
2461 	if (test_bit(TTY_OTHER_CLOSED, &tty->flags))
2462 		mask |= EPOLLHUP;
2463 	if (tty_hung_up_p(file))
2464 		mask |= EPOLLHUP;
2465 	if (tty->ops->write && !tty_is_writelocked(tty) &&
2466 			tty_chars_in_buffer(tty) < WAKEUP_CHARS &&
2467 			tty_write_room(tty) > 0)
2468 		mask |= EPOLLOUT | EPOLLWRNORM;
2469 	return mask;
2470 }
2471 
inq_canon(struct n_tty_data * ldata)2472 static unsigned long inq_canon(struct n_tty_data *ldata)
2473 {
2474 	size_t nr, head, tail;
2475 
2476 	if (ldata->canon_head == ldata->read_tail)
2477 		return 0;
2478 	head = ldata->canon_head;
2479 	tail = ldata->read_tail;
2480 	nr = head - tail;
2481 	/* Skip EOF-chars.. */
2482 	while (MASK(head) != MASK(tail)) {
2483 		if (test_bit(MASK(tail), ldata->read_flags) &&
2484 		    read_buf(ldata, tail) == __DISABLED_CHAR)
2485 			nr--;
2486 		tail++;
2487 	}
2488 	return nr;
2489 }
2490 
n_tty_ioctl(struct tty_struct * tty,unsigned int cmd,unsigned long arg)2491 static int n_tty_ioctl(struct tty_struct *tty, unsigned int cmd,
2492 		       unsigned long arg)
2493 {
2494 	struct n_tty_data *ldata = tty->disc_data;
2495 	unsigned int num;
2496 
2497 	switch (cmd) {
2498 	case TIOCOUTQ:
2499 		return put_user(tty_chars_in_buffer(tty), (int __user *) arg);
2500 	case TIOCINQ:
2501 		down_write(&tty->termios_rwsem);
2502 		if (L_ICANON(tty) && !L_EXTPROC(tty))
2503 			num = inq_canon(ldata);
2504 		else
2505 			num = read_cnt(ldata);
2506 		up_write(&tty->termios_rwsem);
2507 		return put_user(num, (unsigned int __user *) arg);
2508 	default:
2509 		return n_tty_ioctl_helper(tty, cmd, arg);
2510 	}
2511 }
2512 
2513 static struct tty_ldisc_ops n_tty_ops = {
2514 	.owner		 = THIS_MODULE,
2515 	.num		 = N_TTY,
2516 	.name            = "n_tty",
2517 	.open            = n_tty_open,
2518 	.close           = n_tty_close,
2519 	.flush_buffer    = n_tty_flush_buffer,
2520 	.read            = n_tty_read,
2521 	.write           = n_tty_write,
2522 	.ioctl           = n_tty_ioctl,
2523 	.set_termios     = n_tty_set_termios,
2524 	.poll            = n_tty_poll,
2525 	.receive_buf     = n_tty_receive_buf,
2526 	.write_wakeup    = n_tty_write_wakeup,
2527 	.receive_buf2	 = n_tty_receive_buf2,
2528 	.lookahead_buf	 = n_tty_lookahead_flow_ctrl,
2529 };
2530 
2531 /**
2532  *	n_tty_inherit_ops	-	inherit N_TTY methods
2533  *	@ops: struct tty_ldisc_ops where to save N_TTY methods
2534  *
2535  *	Enables a 'subclass' line discipline to 'inherit' N_TTY methods.
2536  */
2537 
n_tty_inherit_ops(struct tty_ldisc_ops * ops)2538 void n_tty_inherit_ops(struct tty_ldisc_ops *ops)
2539 {
2540 	*ops = n_tty_ops;
2541 	ops->owner = NULL;
2542 }
2543 EXPORT_SYMBOL_GPL(n_tty_inherit_ops);
2544 
n_tty_init(void)2545 void __init n_tty_init(void)
2546 {
2547 	tty_register_ldisc(&n_tty_ops);
2548 }
2549