linux/mm/memfd.c

2  * memfd_create system call and file sealing support
7  * This file is released under the GPL.
13 #include <linux/file.h>
68 struct folio *memfd_alloc_folio(struct file *memfd, pgoff_t idx)
184 static unsigned int *memfd_file_seals_ptr(struct file *file)
186 	if (shmem_file(file))
187 		return &SHMEM_I(file_inode(file))->seals;
190 	if (is_file_hugepages(file))
191 		return &HUGETLBFS_I(file_inode(file))->seals;
204 static int memfd_add_seals(struct file *file, unsigned int seals)
206 	struct inode *inode = file_inode(file);
212 	 * Sealing allows multiple parties to share a tmpfs or hugetlbfs file
213 	 * but restrict access to a specific subset of file operations. Seals
221 	 * may prevent some kinds of access to the file. Currently, the
223 	 *   SEAL_SEAL: Prevent further seals from being set on this file
224 	 *   SEAL_SHRINK: Prevent the file from shrinking
225 	 *   SEAL_GROW: Prevent the file from growing
226 	 *   SEAL_WRITE: Prevent write access to the file
227 	 *   SEAL_EXEC: Prevent modification of the exec bits in the file mode
230 	 * must prevent seals from being removed. Therefore, sealing a file
231 	 * only adds a given set of seals to the file, it never touches
239 	 * no plan to support it on other file types.
242 	if (!(file->f_mode & FMODE_WRITE))
249 	file_seals = memfd_file_seals_ptr(file);
261 		error = mapping_deny_writable(file->f_mapping);
265 		error = memfd_wait_for_pins(file->f_mapping);
267 			mapping_allow_writable(file->f_mapping);
286 static int memfd_get_seals(struct file *file)
288 	unsigned int *seals = memfd_file_seals_ptr(file);
293 long memfd_fcntl(struct file *file, unsigned int cmd, unsigned int arg)
299 		error = memfd_add_seals(file, arg);
302 		error = memfd_get_seals(file);
371 int memfd_check_seals_mmap(struct file *file, vm_flags_t *vm_flags_ptr)
374 	unsigned int *seals_ptr = memfd_file_seals_ptr(file);
432 static struct file *alloc_file(const char *name, unsigned int flags)
435 	struct file *file;
438 		file = hugetlb_file_setup(name, 0, VM_NORESERVE,
443 		file = shmem_file_setup(name, 0, VM_NORESERVE);
445 	if (IS_ERR(file))
446 		return file;
447 	file->f_mode |= FMODE_LSEEK | FMODE_PREAD | FMODE_PWRITE;
448 	file->f_flags |= O_LARGEFILE;
451 		struct inode *inode = file_inode(file);
454 		file_seals = memfd_file_seals_ptr(file);
461 		file_seals = memfd_file_seals_ptr(file);
466 	return file;
473 	struct file *file;
491 	file = alloc_file(name, flags);
492 	if (IS_ERR(file)) {
493 		error = PTR_ERR(file);
497 	fd_install(fd, file);