1 // SPDX-License-Identifier: GPL-2.0-or-later
2 /* AFS dynamic root handling
3  *
4  * Copyright (C) 2018 Red Hat, Inc. All Rights Reserved.
5  * Written by David Howells (dhowells@redhat.com)
6  */
7 
8 #include <linux/fs.h>
9 #include <linux/namei.h>
10 #include <linux/dns_resolver.h>
11 #include "internal.h"
12 
13 #define AFS_MIN_DYNROOT_CELL_INO 4 /* Allow for ., .., @cell, .@cell */
14 #define AFS_MAX_DYNROOT_CELL_INO ((unsigned int)INT_MAX)
15 
16 static struct dentry *afs_lookup_atcell(struct inode *dir, struct dentry *dentry, ino_t ino);
17 
18 /*
19  * iget5() comparator for inode created by autocell operations
20  */
21 static int afs_iget5_pseudo_test(struct inode *inode, void *opaque)
22 {
23 	struct afs_fid *fid = opaque;
24 
25 	return inode->i_ino == fid->vnode;
26 }
27 
28 /*
29  * iget5() inode initialiser
30  */
31 static int afs_iget5_pseudo_set(struct inode *inode, void *opaque)
32 {
33 	struct afs_super_info *as = AFS_FS_S(inode->i_sb);
34 	struct afs_vnode *vnode = AFS_FS_I(inode);
35 	struct afs_fid *fid = opaque;
36 
37 	vnode->volume		= as->volume;
38 	vnode->fid		= *fid;
39 	inode->i_ino		= fid->vnode;
40 	inode->i_generation	= fid->unique;
41 	return 0;
42 }
43 
44 /*
45  * Create an inode for an autocell dynamic automount dir.
46  */
47 static struct inode *afs_iget_pseudo_dir(struct super_block *sb, ino_t ino)
48 {
49 	struct afs_vnode *vnode;
50 	struct inode *inode;
51 	struct afs_fid fid = { .vnode = ino, .unique = 1, };
52 
53 	_enter("");
54 
55 	inode = iget5_locked(sb, fid.vnode,
56 			     afs_iget5_pseudo_test, afs_iget5_pseudo_set, &fid);
57 	if (!inode) {
58 		_leave(" = -ENOMEM");
59 		return ERR_PTR(-ENOMEM);
60 	}
61 
62 	_debug("GOT INODE %p { ino=%lu, vl=%llx, vn=%llx, u=%x }",
63 	       inode, inode->i_ino, fid.vid, fid.vnode, fid.unique);
64 
65 	vnode = AFS_FS_I(inode);
66 
67 	if (inode->i_state & I_NEW) {
68 		netfs_inode_init(&vnode->netfs, NULL, false);
69 		simple_inode_init_ts(inode);
70 		set_nlink(inode, 2);
71 		inode->i_size		= 0;
72 		inode->i_mode		= S_IFDIR | 0555;
73 		inode->i_op		= &afs_autocell_inode_operations;
74 		inode->i_uid		= GLOBAL_ROOT_UID;
75 		inode->i_gid		= GLOBAL_ROOT_GID;
76 		inode->i_blocks		= 0;
77 		inode->i_generation	= 0;
78 		inode->i_flags		|= S_AUTOMOUNT | S_NOATIME;
79 
80 		set_bit(AFS_VNODE_PSEUDODIR, &vnode->flags);
81 		set_bit(AFS_VNODE_MOUNTPOINT, &vnode->flags);
82 
83 		unlock_new_inode(inode);
84 	}
85 	_leave(" = %p", inode);
86 	return inode;
87 }
88 
89 /*
90  * Try to automount the mountpoint with pseudo directory, if the autocell
91  * option is set.
92  */
93 static struct dentry *afs_dynroot_lookup_cell(struct inode *dir, struct dentry *dentry,
94 					      unsigned int flags)
95 {
96 	struct afs_cell *cell = NULL;
97 	struct afs_net *net = afs_d2net(dentry);
98 	struct inode *inode = NULL;
99 	const char *name = dentry->d_name.name;
100 	size_t len = dentry->d_name.len;
101 	bool dotted = false;
102 	int ret = -ENOENT;
103 
104 	/* Names prefixed with a dot are R/W mounts. */
105 	if (name[0] == '.') {
106 		name++;
107 		len--;
108 		dotted = true;
109 	}
110 
111 	cell = afs_lookup_cell(net, name, len, NULL, false,
112 			       afs_cell_trace_use_lookup_dynroot);
113 	if (IS_ERR(cell)) {
114 		ret = PTR_ERR(cell);
115 		goto out_no_cell;
116 	}
117 
118 	inode = afs_iget_pseudo_dir(dir->i_sb, cell->dynroot_ino * 2 + dotted);
119 	if (IS_ERR(inode)) {
120 		ret = PTR_ERR(inode);
121 		goto out;
122 	}
123 
124 	dentry->d_fsdata = cell;
125 	return d_splice_alias(inode, dentry);
126 
127 out:
128 	afs_unuse_cell(cell, afs_cell_trace_unuse_lookup_dynroot);
129 out_no_cell:
130 	if (!inode)
131 		return d_splice_alias(inode, dentry);
132 	return ret == -ENOENT ? NULL : ERR_PTR(ret);
133 }
134 
135 /*
136  * Look up an entry in a dynroot directory.
137  */
138 static struct dentry *afs_dynroot_lookup(struct inode *dir, struct dentry *dentry,
139 					 unsigned int flags)
140 {
141 	_enter("%pd", dentry);
142 
143 	if (flags & LOOKUP_CREATE)
144 		return ERR_PTR(-EOPNOTSUPP);
145 
146 	if (dentry->d_name.len >= AFSNAMEMAX) {
147 		_leave(" = -ENAMETOOLONG");
148 		return ERR_PTR(-ENAMETOOLONG);
149 	}
150 
151 	if (dentry->d_name.len == 5 &&
152 	    memcmp(dentry->d_name.name, "@cell", 5) == 0)
153 		return afs_lookup_atcell(dir, dentry, 2);
154 
155 	if (dentry->d_name.len == 6 &&
156 	    memcmp(dentry->d_name.name, ".@cell", 6) == 0)
157 		return afs_lookup_atcell(dir, dentry, 3);
158 
159 	return afs_dynroot_lookup_cell(dir, dentry, flags);
160 }
161 
162 const struct inode_operations afs_dynroot_inode_operations = {
163 	.lookup		= afs_dynroot_lookup,
164 };
165 
166 static void afs_dynroot_d_release(struct dentry *dentry)
167 {
168 	struct afs_cell *cell = dentry->d_fsdata;
169 
170 	afs_unuse_cell(cell, afs_cell_trace_unuse_dynroot_mntpt);
171 }
172 
173 /*
174  * Keep @cell symlink dentries around, but only keep cell autodirs when they're
175  * being used.
176  */
177 static int afs_dynroot_delete_dentry(const struct dentry *dentry)
178 {
179 	const struct qstr *name = &dentry->d_name;
180 
181 	if (name->len == 5 && memcmp(name->name, "@cell", 5) == 0)
182 		return 0;
183 	if (name->len == 6 && memcmp(name->name, ".@cell", 6) == 0)
184 		return 0;
185 	return 1;
186 }
187 
188 const struct dentry_operations afs_dynroot_dentry_operations = {
189 	.d_delete	= afs_dynroot_delete_dentry,
190 	.d_release	= afs_dynroot_d_release,
191 	.d_automount	= afs_d_automount,
192 };
193 
194 static void afs_atcell_delayed_put_cell(void *arg)
195 {
196 	struct afs_cell *cell = arg;
197 
198 	afs_put_cell(cell, afs_cell_trace_put_atcell);
199 }
200 
201 /*
202  * Read @cell or .@cell symlinks.
203  */
204 static const char *afs_atcell_get_link(struct dentry *dentry, struct inode *inode,
205 				       struct delayed_call *done)
206 {
207 	struct afs_vnode *vnode = AFS_FS_I(inode);
208 	struct afs_cell *cell;
209 	struct afs_net *net = afs_i2net(inode);
210 	const char *name;
211 	bool dotted = vnode->fid.vnode == 3;
212 
213 	if (!rcu_access_pointer(net->ws_cell))
214 		return ERR_PTR(-ENOENT);
215 
216 	if (!dentry) {
217 		/* We're in RCU-pathwalk. */
218 		cell = rcu_dereference(net->ws_cell);
219 		if (dotted)
220 			name = cell->name - 1;
221 		else
222 			name = cell->name;
223 		/* Shouldn't need to set a delayed call. */
224 		return name;
225 	}
226 
227 	down_read(&net->cells_lock);
228 
229 	cell = rcu_dereference_protected(net->ws_cell, lockdep_is_held(&net->cells_lock));
230 	if (dotted)
231 		name = cell->name - 1;
232 	else
233 		name = cell->name;
234 	afs_get_cell(cell, afs_cell_trace_get_atcell);
235 	set_delayed_call(done, afs_atcell_delayed_put_cell, cell);
236 
237 	up_read(&net->cells_lock);
238 	return name;
239 }
240 
241 static const struct inode_operations afs_atcell_inode_operations = {
242 	.get_link	= afs_atcell_get_link,
243 };
244 
245 /*
246  * Create an inode for the @cell or .@cell symlinks.
247  */
248 static struct dentry *afs_lookup_atcell(struct inode *dir, struct dentry *dentry, ino_t ino)
249 {
250 	struct afs_vnode *vnode;
251 	struct inode *inode;
252 	struct afs_fid fid = { .vnode = ino, .unique = 1, };
253 
254 	inode = iget5_locked(dir->i_sb, fid.vnode,
255 			     afs_iget5_pseudo_test, afs_iget5_pseudo_set, &fid);
256 	if (!inode)
257 		return ERR_PTR(-ENOMEM);
258 
259 	vnode = AFS_FS_I(inode);
260 
261 	if (inode->i_state & I_NEW) {
262 		netfs_inode_init(&vnode->netfs, NULL, false);
263 		simple_inode_init_ts(inode);
264 		set_nlink(inode, 1);
265 		inode->i_size		= 0;
266 		inode->i_mode		= S_IFLNK | 0555;
267 		inode->i_op		= &afs_atcell_inode_operations;
268 		inode->i_uid		= GLOBAL_ROOT_UID;
269 		inode->i_gid		= GLOBAL_ROOT_GID;
270 		inode->i_blocks		= 0;
271 		inode->i_generation	= 0;
272 		inode->i_flags		|= S_NOATIME;
273 
274 		unlock_new_inode(inode);
275 	}
276 	return d_splice_alias(inode, dentry);
277 }
278 
279 /*
280  * Transcribe the cell database into readdir content under the RCU read lock.
281  * Each cell produces two entries, one prefixed with a dot and one not.
282  */
283 static int afs_dynroot_readdir_cells(struct afs_net *net, struct dir_context *ctx)
284 {
285 	const struct afs_cell *cell;
286 	loff_t newpos;
287 
288 	_enter("%llu", ctx->pos);
289 
290 	for (;;) {
291 		unsigned int ix = ctx->pos >> 1;
292 
293 		cell = idr_get_next(&net->cells_dyn_ino, &ix);
294 		if (!cell)
295 			return 0;
296 		if (READ_ONCE(cell->state) == AFS_CELL_REMOVING ||
297 		    READ_ONCE(cell->state) == AFS_CELL_DEAD) {
298 			ctx->pos += 2;
299 			ctx->pos &= ~1;
300 			continue;
301 		}
302 
303 		newpos = ix << 1;
304 		if (newpos > ctx->pos)
305 			ctx->pos = newpos;
306 
307 		_debug("pos %llu -> cell %u", ctx->pos, cell->dynroot_ino);
308 
309 		if ((ctx->pos & 1) == 0) {
310 			if (!dir_emit(ctx, cell->name, cell->name_len,
311 				      cell->dynroot_ino, DT_DIR))
312 				return 0;
313 			ctx->pos++;
314 		}
315 		if ((ctx->pos & 1) == 1) {
316 			if (!dir_emit(ctx, cell->name - 1, cell->name_len + 1,
317 				      cell->dynroot_ino + 1, DT_DIR))
318 				return 0;
319 			ctx->pos++;
320 		}
321 	}
322 	return 0;
323 }
324 
325 /*
326  * Read the AFS dynamic root directory.  This produces a list of cellnames,
327  * dotted and undotted, along with @cell and .@cell links if configured.
328  */
329 static int afs_dynroot_readdir(struct file *file, struct dir_context *ctx)
330 {
331 	struct afs_net *net = afs_d2net(file->f_path.dentry);
332 	int ret = 0;
333 
334 	if (!dir_emit_dots(file, ctx))
335 		return 0;
336 
337 	if (ctx->pos == 2) {
338 		if (rcu_access_pointer(net->ws_cell) &&
339 		    !dir_emit(ctx, "@cell", 5, 2, DT_LNK))
340 			return 0;
341 		ctx->pos = 3;
342 	}
343 	if (ctx->pos == 3) {
344 		if (rcu_access_pointer(net->ws_cell) &&
345 		    !dir_emit(ctx, ".@cell", 6, 3, DT_LNK))
346 			return 0;
347 		ctx->pos = 4;
348 	}
349 
350 	if ((unsigned long long)ctx->pos <= AFS_MAX_DYNROOT_CELL_INO) {
351 		down_read(&net->cells_lock);
352 		ret = afs_dynroot_readdir_cells(net, ctx);
353 		up_read(&net->cells_lock);
354 	}
355 	return ret;
356 }
357 
358 static const struct file_operations afs_dynroot_file_operations = {
359 	.llseek		= generic_file_llseek,
360 	.read		= generic_read_dir,
361 	.iterate_shared	= afs_dynroot_readdir,
362 	.fsync		= noop_fsync,
363 };
364 
365 /*
366  * Create an inode for a dynamic root directory.
367  */
368 struct inode *afs_dynroot_iget_root(struct super_block *sb)
369 {
370 	struct afs_super_info *as = AFS_FS_S(sb);
371 	struct afs_vnode *vnode;
372 	struct inode *inode;
373 	struct afs_fid fid = { .vid = 0, .vnode = 1, .unique = 1,};
374 
375 	if (as->volume)
376 		fid.vid = as->volume->vid;
377 
378 	inode = iget5_locked(sb, fid.vnode,
379 			     afs_iget5_pseudo_test, afs_iget5_pseudo_set, &fid);
380 	if (!inode)
381 		return ERR_PTR(-ENOMEM);
382 
383 	vnode = AFS_FS_I(inode);
384 
385 	/* there shouldn't be an existing inode */
386 	if (inode->i_state & I_NEW) {
387 		netfs_inode_init(&vnode->netfs, NULL, false);
388 		simple_inode_init_ts(inode);
389 		set_nlink(inode, 2);
390 		inode->i_size		= 0;
391 		inode->i_mode		= S_IFDIR | 0555;
392 		inode->i_op		= &afs_dynroot_inode_operations;
393 		inode->i_fop		= &afs_dynroot_file_operations;
394 		inode->i_uid		= GLOBAL_ROOT_UID;
395 		inode->i_gid		= GLOBAL_ROOT_GID;
396 		inode->i_blocks		= 0;
397 		inode->i_generation	= 0;
398 		inode->i_flags		|= S_NOATIME;
399 
400 		set_bit(AFS_VNODE_PSEUDODIR, &vnode->flags);
401 		unlock_new_inode(inode);
402 	}
403 	_leave(" = %p", inode);
404 	return inode;
405 }
406