1/* SPDX-License-Identifier: GPL-2.0 */
2/*
3 * fscrypt.h: declarations for per-file encryption
4 *
5 * Filesystems that implement per-file encryption must include this header
6 * file.
7 *
8 * Copyright (C) 2015, Google, Inc.
9 *
10 * Written by Michael Halcrow, 2015.
11 * Modified by Jaegeuk Kim, 2015.
12 */
13#ifndef _LINUX_FSCRYPT_H
14#define _LINUX_FSCRYPT_H
15
16#include <linux/fs.h>
17#include <linux/mm.h>
18#include <linux/slab.h>
19
20#define FS_CRYPTO_BLOCK_SIZE 16
21
22struct fscrypt_ctx;
23struct fscrypt_info;
24
25struct fscrypt_str {
26 unsigned char *name;
27 u32 len;
28};
29
30struct fscrypt_name {
31 const struct qstr *usr_fname;
32 struct fscrypt_str disk_name;
33 u32 hash;
34 u32 minor_hash;
35 struct fscrypt_str crypto_buf;
36};
37
38#define FSTR_INIT(n, l) { .name = n, .len = l }
39#define FSTR_TO_QSTR(f) QSTR_INIT((f)->name, (f)->len)
40#define fname_name(p) ((p)->disk_name.name)
41#define fname_len(p) ((p)->disk_name.len)
42
43/* Maximum value for the third parameter of fscrypt_operations.set_context(). */
44#define FSCRYPT_SET_CONTEXT_MAX_SIZE 28
45
46#ifdef CONFIG_FS_ENCRYPTION
47/*
48 * fscrypt superblock flags
49 */
50#define FS_CFLG_OWN_PAGES (1U << 1)
51
52/*
53 * crypto operations for filesystems
54 */
55struct fscrypt_operations {
56 unsigned int flags;
57 const char *key_prefix;
58 int (*get_context)(struct inode *, void *, size_t);
59 int (*set_context)(struct inode *, const void *, size_t, void *);
60 bool (*dummy_context)(struct inode *);
61 bool (*empty_dir)(struct inode *);
62 unsigned int max_namelen;
63};
64
65struct fscrypt_ctx {
66 union {
67 struct {
68 struct page *bounce_page; /* Ciphertext page */
69 struct page *control_page; /* Original page */
70 } w;
71 struct {
72 struct bio *bio;
73 struct work_struct work;
74 } r;
75 struct list_head free_list; /* Free list */
76 };
77 u8 flags; /* Flags */
78};
79
80static inline bool fscrypt_has_encryption_key(const struct inode *inode)
81{
82 return (inode->i_crypt_info != NULL);
83}
84
85static inline bool fscrypt_dummy_context_enabled(struct inode *inode)
86{
87 return inode->i_sb->s_cop->dummy_context &&
88 inode->i_sb->s_cop->dummy_context(inode);
89}
90
91/* crypto.c */
92extern void fscrypt_enqueue_decrypt_work(struct work_struct *);
93extern struct fscrypt_ctx *fscrypt_get_ctx(const struct inode *, gfp_t);
94extern void fscrypt_release_ctx(struct fscrypt_ctx *);
95extern struct page *fscrypt_encrypt_page(const struct inode *, struct page *,
96 unsigned int, unsigned int,
97 u64, gfp_t);
98extern int fscrypt_decrypt_page(const struct inode *, struct page *, unsigned int,
99 unsigned int, u64);
100
101static inline struct page *fscrypt_control_page(struct page *page)
102{
103 return ((struct fscrypt_ctx *)page_private(page))->w.control_page;
104}
105
106extern void fscrypt_restore_control_page(struct page *);
107
108/* policy.c */
109extern int fscrypt_ioctl_set_policy(struct file *, const void __user *);
110extern int fscrypt_ioctl_get_policy(struct file *, void __user *);
111extern int fscrypt_has_permitted_context(struct inode *, struct inode *);
112extern int fscrypt_inherit_context(struct inode *, struct inode *,
113 void *, bool);
114/* keyinfo.c */
115extern int fscrypt_get_encryption_info(struct inode *);
116extern void fscrypt_put_encryption_info(struct inode *);
117
118/* fname.c */
119extern int fscrypt_setup_filename(struct inode *, const struct qstr *,
120 int lookup, struct fscrypt_name *);
121
122static inline void fscrypt_free_filename(struct fscrypt_name *fname)
123{
124 kfree(fname->crypto_buf.name);
125}
126
127extern int fscrypt_fname_alloc_buffer(const struct inode *, u32,
128 struct fscrypt_str *);
129extern void fscrypt_fname_free_buffer(struct fscrypt_str *);
130extern int fscrypt_fname_disk_to_usr(struct inode *, u32, u32,
131 const struct fscrypt_str *, struct fscrypt_str *);
132
133#define FSCRYPT_FNAME_MAX_UNDIGESTED_SIZE 32
134
135/* Extracts the second-to-last ciphertext block; see explanation below */
136#define FSCRYPT_FNAME_DIGEST(name, len) \
137 ((name) + round_down((len) - FS_CRYPTO_BLOCK_SIZE - 1, \
138 FS_CRYPTO_BLOCK_SIZE))
139
140#define FSCRYPT_FNAME_DIGEST_SIZE FS_CRYPTO_BLOCK_SIZE
141
142/**
143 * fscrypt_digested_name - alternate identifier for an on-disk filename
144 *
145 * When userspace lists an encrypted directory without access to the key,
146 * filenames whose ciphertext is longer than FSCRYPT_FNAME_MAX_UNDIGESTED_SIZE
147 * bytes are shown in this abbreviated form (base64-encoded) rather than as the
148 * full ciphertext (base64-encoded). This is necessary to allow supporting
149 * filenames up to NAME_MAX bytes, since base64 encoding expands the length.
150 *
151 * To make it possible for filesystems to still find the correct directory entry
152 * despite not knowing the full on-disk name, we encode any filesystem-specific
153 * 'hash' and/or 'minor_hash' which the filesystem may need for its lookups,
154 * followed by the second-to-last ciphertext block of the filename. Due to the
155 * use of the CBC-CTS encryption mode, the second-to-last ciphertext block
156 * depends on the full plaintext. (Note that ciphertext stealing causes the
157 * last two blocks to appear "flipped".) This makes accidental collisions very
158 * unlikely: just a 1 in 2^128 chance for two filenames to collide even if they
159 * share the same filesystem-specific hashes.
160 *
161 * However, this scheme isn't immune to intentional collisions, which can be
162 * created by anyone able to create arbitrary plaintext filenames and view them
163 * without the key. Making the "digest" be a real cryptographic hash like
164 * SHA-256 over the full ciphertext would prevent this, although it would be
165 * less efficient and harder to implement, especially since the filesystem would
166 * need to calculate it for each directory entry examined during a search.
167 */
168struct fscrypt_digested_name {
169 u32 hash;
170 u32 minor_hash;
171 u8 digest[FSCRYPT_FNAME_DIGEST_SIZE];
172};
173
174/**
175 * fscrypt_match_name() - test whether the given name matches a directory entry
176 * @fname: the name being searched for
177 * @de_name: the name from the directory entry
178 * @de_name_len: the length of @de_name in bytes
179 *
180 * Normally @fname->disk_name will be set, and in that case we simply compare
181 * that to the name stored in the directory entry. The only exception is that
182 * if we don't have the key for an encrypted directory and a filename in it is
183 * very long, then we won't have the full disk_name and we'll instead need to
184 * match against the fscrypt_digested_name.
185 *
186 * Return: %true if the name matches, otherwise %false.
187 */
188static inline bool fscrypt_match_name(const struct fscrypt_name *fname,
189 const u8 *de_name, u32 de_name_len)
190{
191 if (unlikely(!fname->disk_name.name)) {
192 const struct fscrypt_digested_name *n =
193 (const void *)fname->crypto_buf.name;
194 if (WARN_ON_ONCE(fname->usr_fname->name[0] != '_'))
195 return false;
196 if (de_name_len <= FSCRYPT_FNAME_MAX_UNDIGESTED_SIZE)
197 return false;
198 return !memcmp(FSCRYPT_FNAME_DIGEST(de_name, de_name_len),
199 n->digest, FSCRYPT_FNAME_DIGEST_SIZE);
200 }
201
202 if (de_name_len != fname->disk_name.len)
203 return false;
204 return !memcmp(de_name, fname->disk_name.name, fname->disk_name.len);
205}
206
207/* bio.c */
208extern void fscrypt_decrypt_bio(struct bio *);
209extern void fscrypt_enqueue_decrypt_bio(struct fscrypt_ctx *ctx,
210 struct bio *bio);
211extern void fscrypt_pullback_bio_page(struct page **, bool);
212extern int fscrypt_zeroout_range(const struct inode *, pgoff_t, sector_t,
213 unsigned int);
214
215/* hooks.c */
216extern int fscrypt_file_open(struct inode *inode, struct file *filp);
217extern int __fscrypt_prepare_link(struct inode *inode, struct inode *dir);
218extern int __fscrypt_prepare_rename(struct inode *old_dir,
219 struct dentry *old_dentry,
220 struct inode *new_dir,
221 struct dentry *new_dentry,
222 unsigned int flags);
223extern int __fscrypt_prepare_lookup(struct inode *dir, struct dentry *dentry);
224extern int __fscrypt_prepare_symlink(struct inode *dir, unsigned int len,
225 unsigned int max_len,
226 struct fscrypt_str *disk_link);
227extern int __fscrypt_encrypt_symlink(struct inode *inode, const char *target,
228 unsigned int len,
229 struct fscrypt_str *disk_link);
230extern const char *fscrypt_get_symlink(struct inode *inode, const void *caddr,
231 unsigned int max_size,
232 struct delayed_call *done);
233#else /* !CONFIG_FS_ENCRYPTION */
234
235static inline bool fscrypt_has_encryption_key(const struct inode *inode)
236{
237 return false;
238}
239
240static inline bool fscrypt_dummy_context_enabled(struct inode *inode)
241{
242 return false;
243}
244
245/* crypto.c */
246static inline void fscrypt_enqueue_decrypt_work(struct work_struct *work)
247{
248}
249
250static inline struct fscrypt_ctx *fscrypt_get_ctx(const struct inode *inode,
251 gfp_t gfp_flags)
252{
253 return ERR_PTR(-EOPNOTSUPP);
254}
255
256static inline void fscrypt_release_ctx(struct fscrypt_ctx *ctx)
257{
258 return;
259}
260
261static inline struct page *fscrypt_encrypt_page(const struct inode *inode,
262 struct page *page,
263 unsigned int len,
264 unsigned int offs,
265 u64 lblk_num, gfp_t gfp_flags)
266{
267 return ERR_PTR(-EOPNOTSUPP);
268}
269
270static inline int fscrypt_decrypt_page(const struct inode *inode,
271 struct page *page,
272 unsigned int len, unsigned int offs,
273 u64 lblk_num)
274{
275 return -EOPNOTSUPP;
276}
277
278static inline struct page *fscrypt_control_page(struct page *page)
279{
280 WARN_ON_ONCE(1);
281 return ERR_PTR(-EINVAL);
282}
283
284static inline void fscrypt_restore_control_page(struct page *page)
285{
286 return;
287}
288
289/* policy.c */
290static inline int fscrypt_ioctl_set_policy(struct file *filp,
291 const void __user *arg)
292{
293 return -EOPNOTSUPP;
294}
295
296static inline int fscrypt_ioctl_get_policy(struct file *filp, void __user *arg)
297{
298 return -EOPNOTSUPP;
299}
300
301static inline int fscrypt_has_permitted_context(struct inode *parent,
302 struct inode *child)
303{
304 return 0;
305}
306
307static inline int fscrypt_inherit_context(struct inode *parent,
308 struct inode *child,
309 void *fs_data, bool preload)
310{
311 return -EOPNOTSUPP;
312}
313
314/* keyinfo.c */
315static inline int fscrypt_get_encryption_info(struct inode *inode)
316{
317 return -EOPNOTSUPP;
318}
319
320static inline void fscrypt_put_encryption_info(struct inode *inode)
321{
322 return;
323}
324
325 /* fname.c */
326static inline int fscrypt_setup_filename(struct inode *dir,
327 const struct qstr *iname,
328 int lookup, struct fscrypt_name *fname)
329{
330 if (IS_ENCRYPTED(dir))
331 return -EOPNOTSUPP;
332
333 memset(fname, 0, sizeof(struct fscrypt_name));
334 fname->usr_fname = iname;
335 fname->disk_name.name = (unsigned char *)iname->name;
336 fname->disk_name.len = iname->len;
337 return 0;
338}
339
340static inline void fscrypt_free_filename(struct fscrypt_name *fname)
341{
342 return;
343}
344
345static inline int fscrypt_fname_alloc_buffer(const struct inode *inode,
346 u32 max_encrypted_len,
347 struct fscrypt_str *crypto_str)
348{
349 return -EOPNOTSUPP;
350}
351
352static inline void fscrypt_fname_free_buffer(struct fscrypt_str *crypto_str)
353{
354 return;
355}
356
357static inline int fscrypt_fname_disk_to_usr(struct inode *inode,
358 u32 hash, u32 minor_hash,
359 const struct fscrypt_str *iname,
360 struct fscrypt_str *oname)
361{
362 return -EOPNOTSUPP;
363}
364
365static inline bool fscrypt_match_name(const struct fscrypt_name *fname,
366 const u8 *de_name, u32 de_name_len)
367{
368 /* Encryption support disabled; use standard comparison */
369 if (de_name_len != fname->disk_name.len)
370 return false;
371 return !memcmp(de_name, fname->disk_name.name, fname->disk_name.len);
372}
373
374/* bio.c */
375static inline void fscrypt_decrypt_bio(struct bio *bio)
376{
377}
378
379static inline void fscrypt_enqueue_decrypt_bio(struct fscrypt_ctx *ctx,
380 struct bio *bio)
381{
382}
383
384static inline void fscrypt_pullback_bio_page(struct page **page, bool restore)
385{
386 return;
387}
388
389static inline int fscrypt_zeroout_range(const struct inode *inode, pgoff_t lblk,
390 sector_t pblk, unsigned int len)
391{
392 return -EOPNOTSUPP;
393}
394
395/* hooks.c */
396
397static inline int fscrypt_file_open(struct inode *inode, struct file *filp)
398{
399 if (IS_ENCRYPTED(inode))
400 return -EOPNOTSUPP;
401 return 0;
402}
403
404static inline int __fscrypt_prepare_link(struct inode *inode,
405 struct inode *dir)
406{
407 return -EOPNOTSUPP;
408}
409
410static inline int __fscrypt_prepare_rename(struct inode *old_dir,
411 struct dentry *old_dentry,
412 struct inode *new_dir,
413 struct dentry *new_dentry,
414 unsigned int flags)
415{
416 return -EOPNOTSUPP;
417}
418
419static inline int __fscrypt_prepare_lookup(struct inode *dir,
420 struct dentry *dentry)
421{
422 return -EOPNOTSUPP;
423}
424
425static inline int __fscrypt_prepare_symlink(struct inode *dir,
426 unsigned int len,
427 unsigned int max_len,
428 struct fscrypt_str *disk_link)
429{
430 return -EOPNOTSUPP;
431}
432
433
434static inline int __fscrypt_encrypt_symlink(struct inode *inode,
435 const char *target,
436 unsigned int len,
437 struct fscrypt_str *disk_link)
438{
439 return -EOPNOTSUPP;
440}
441
442static inline const char *fscrypt_get_symlink(struct inode *inode,
443 const void *caddr,
444 unsigned int max_size,
445 struct delayed_call *done)
446{
447 return ERR_PTR(-EOPNOTSUPP);
448}
449#endif /* !CONFIG_FS_ENCRYPTION */
450
451/**
452 * fscrypt_require_key - require an inode's encryption key
453 * @inode: the inode we need the key for
454 *
455 * If the inode is encrypted, set up its encryption key if not already done.
456 * Then require that the key be present and return -ENOKEY otherwise.
457 *
458 * No locks are needed, and the key will live as long as the struct inode --- so
459 * it won't go away from under you.
460 *
461 * Return: 0 on success, -ENOKEY if the key is missing, or another -errno code
462 * if a problem occurred while setting up the encryption key.
463 */
464static inline int fscrypt_require_key(struct inode *inode)
465{
466 if (IS_ENCRYPTED(inode)) {
467 int err = fscrypt_get_encryption_info(inode);
468
469 if (err)
470 return err;
471 if (!fscrypt_has_encryption_key(inode))
472 return -ENOKEY;
473 }
474 return 0;
475}
476
477/**
478 * fscrypt_prepare_link - prepare to link an inode into a possibly-encrypted directory
479 * @old_dentry: an existing dentry for the inode being linked
480 * @dir: the target directory
481 * @dentry: negative dentry for the target filename
482 *
483 * A new link can only be added to an encrypted directory if the directory's
484 * encryption key is available --- since otherwise we'd have no way to encrypt
485 * the filename. Therefore, we first set up the directory's encryption key (if
486 * not already done) and return an error if it's unavailable.
487 *
488 * We also verify that the link will not violate the constraint that all files
489 * in an encrypted directory tree use the same encryption policy.
490 *
491 * Return: 0 on success, -ENOKEY if the directory's encryption key is missing,
492 * -EXDEV if the link would result in an inconsistent encryption policy, or
493 * another -errno code.
494 */
495static inline int fscrypt_prepare_link(struct dentry *old_dentry,
496 struct inode *dir,
497 struct dentry *dentry)
498{
499 if (IS_ENCRYPTED(dir))
500 return __fscrypt_prepare_link(d_inode(old_dentry), dir);
501 return 0;
502}
503
504/**
505 * fscrypt_prepare_rename - prepare for a rename between possibly-encrypted directories
506 * @old_dir: source directory
507 * @old_dentry: dentry for source file
508 * @new_dir: target directory
509 * @new_dentry: dentry for target location (may be negative unless exchanging)
510 * @flags: rename flags (we care at least about %RENAME_EXCHANGE)
511 *
512 * Prepare for ->rename() where the source and/or target directories may be
513 * encrypted. A new link can only be added to an encrypted directory if the
514 * directory's encryption key is available --- since otherwise we'd have no way
515 * to encrypt the filename. A rename to an existing name, on the other hand,
516 * *is* cryptographically possible without the key. However, we take the more
517 * conservative approach and just forbid all no-key renames.
518 *
519 * We also verify that the rename will not violate the constraint that all files
520 * in an encrypted directory tree use the same encryption policy.
521 *
522 * Return: 0 on success, -ENOKEY if an encryption key is missing, -EXDEV if the
523 * rename would cause inconsistent encryption policies, or another -errno code.
524 */
525static inline int fscrypt_prepare_rename(struct inode *old_dir,
526 struct dentry *old_dentry,
527 struct inode *new_dir,
528 struct dentry *new_dentry,
529 unsigned int flags)
530{
531 if (IS_ENCRYPTED(old_dir) || IS_ENCRYPTED(new_dir))
532 return __fscrypt_prepare_rename(old_dir, old_dentry,
533 new_dir, new_dentry, flags);
534 return 0;
535}
536
537/**
538 * fscrypt_prepare_lookup - prepare to lookup a name in a possibly-encrypted directory
539 * @dir: directory being searched
540 * @dentry: filename being looked up
541 * @flags: lookup flags
542 *
543 * Prepare for ->lookup() in a directory which may be encrypted. Lookups can be
544 * done with or without the directory's encryption key; without the key,
545 * filenames are presented in encrypted form. Therefore, we'll try to set up
546 * the directory's encryption key, but even without it the lookup can continue.
547 *
548 * To allow invalidating stale dentries if the directory's encryption key is
549 * added later, we also install a custom ->d_revalidate() method and use the
550 * DCACHE_ENCRYPTED_WITH_KEY flag to indicate whether a given dentry is a
551 * plaintext name (flag set) or a ciphertext name (flag cleared).
552 *
553 * Return: 0 on success, -errno if a problem occurred while setting up the
554 * encryption key
555 */
556static inline int fscrypt_prepare_lookup(struct inode *dir,
557 struct dentry *dentry,
558 unsigned int flags)
559{
560 if (IS_ENCRYPTED(dir))
561 return __fscrypt_prepare_lookup(dir, dentry);
562 return 0;
563}
564
565/**
566 * fscrypt_prepare_setattr - prepare to change a possibly-encrypted inode's attributes
567 * @dentry: dentry through which the inode is being changed
568 * @attr: attributes to change
569 *
570 * Prepare for ->setattr() on a possibly-encrypted inode. On an encrypted file,
571 * most attribute changes are allowed even without the encryption key. However,
572 * without the encryption key we do have to forbid truncates. This is needed
573 * because the size being truncated to may not be a multiple of the filesystem
574 * block size, and in that case we'd have to decrypt the final block, zero the
575 * portion past i_size, and re-encrypt it. (We *could* allow truncating to a
576 * filesystem block boundary, but it's simpler to just forbid all truncates ---
577 * and we already forbid all other contents modifications without the key.)
578 *
579 * Return: 0 on success, -ENOKEY if the key is missing, or another -errno code
580 * if a problem occurred while setting up the encryption key.
581 */
582static inline int fscrypt_prepare_setattr(struct dentry *dentry,
583 struct iattr *attr)
584{
585 if (attr->ia_valid & ATTR_SIZE)
586 return fscrypt_require_key(d_inode(dentry));
587 return 0;
588}
589
590/**
591 * fscrypt_prepare_symlink - prepare to create a possibly-encrypted symlink
592 * @dir: directory in which the symlink is being created
593 * @target: plaintext symlink target
594 * @len: length of @target excluding null terminator
595 * @max_len: space the filesystem has available to store the symlink target
596 * @disk_link: (out) the on-disk symlink target being prepared
597 *
598 * This function computes the size the symlink target will require on-disk,
599 * stores it in @disk_link->len, and validates it against @max_len. An
600 * encrypted symlink may be longer than the original.
601 *
602 * Additionally, @disk_link->name is set to @target if the symlink will be
603 * unencrypted, but left NULL if the symlink will be encrypted. For encrypted
604 * symlinks, the filesystem must call fscrypt_encrypt_symlink() to create the
605 * on-disk target later. (The reason for the two-step process is that some
606 * filesystems need to know the size of the symlink target before creating the
607 * inode, e.g. to determine whether it will be a "fast" or "slow" symlink.)
608 *
609 * Return: 0 on success, -ENAMETOOLONG if the symlink target is too long,
610 * -ENOKEY if the encryption key is missing, or another -errno code if a problem
611 * occurred while setting up the encryption key.
612 */
613static inline int fscrypt_prepare_symlink(struct inode *dir,
614 const char *target,
615 unsigned int len,
616 unsigned int max_len,
617 struct fscrypt_str *disk_link)
618{
619 if (IS_ENCRYPTED(dir) || fscrypt_dummy_context_enabled(dir))
620 return __fscrypt_prepare_symlink(dir, len, max_len, disk_link);
621
622 disk_link->name = (unsigned char *)target;
623 disk_link->len = len + 1;
624 if (disk_link->len > max_len)
625 return -ENAMETOOLONG;
626 return 0;
627}
628
629/**
630 * fscrypt_encrypt_symlink - encrypt the symlink target if needed
631 * @inode: symlink inode
632 * @target: plaintext symlink target
633 * @len: length of @target excluding null terminator
634 * @disk_link: (in/out) the on-disk symlink target being prepared
635 *
636 * If the symlink target needs to be encrypted, then this function encrypts it
637 * into @disk_link->name. fscrypt_prepare_symlink() must have been called
638 * previously to compute @disk_link->len. If the filesystem did not allocate a
639 * buffer for @disk_link->name after calling fscrypt_prepare_link(), then one
640 * will be kmalloc()'ed and the filesystem will be responsible for freeing it.
641 *
642 * Return: 0 on success, -errno on failure
643 */
644static inline int fscrypt_encrypt_symlink(struct inode *inode,
645 const char *target,
646 unsigned int len,
647 struct fscrypt_str *disk_link)
648{
649 if (IS_ENCRYPTED(inode))
650 return __fscrypt_encrypt_symlink(inode, target, len, disk_link);
651 return 0;
652}
653
654#endif /* _LINUX_FSCRYPT_H */
655