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1/* SPDX-License-Identifier: GPL-2.0 */
2/*
3 * fscrypt_supp.h
4 *
5 * This is included by filesystems configured with encryption support.
6 */
7
8#ifndef _LINUX_FSCRYPT_SUPP_H
9#define _LINUX_FSCRYPT_SUPP_H
10
11#include <linux/fscrypt_common.h>
12
13/* crypto.c */
14extern struct kmem_cache *fscrypt_info_cachep;
15extern struct fscrypt_ctx *fscrypt_get_ctx(const struct inode *, gfp_t);
16extern void fscrypt_release_ctx(struct fscrypt_ctx *);
17extern struct page *fscrypt_encrypt_page(const struct inode *, struct page *,
18 unsigned int, unsigned int,
19 u64, gfp_t);
20extern int fscrypt_decrypt_page(const struct inode *, struct page *, unsigned int,
21 unsigned int, u64);
22extern void fscrypt_restore_control_page(struct page *);
23
24extern const struct dentry_operations fscrypt_d_ops;
25
26static inline void fscrypt_set_d_op(struct dentry *dentry)
27{
28 d_set_d_op(dentry, &fscrypt_d_ops);
29}
30
31static inline void fscrypt_set_encrypted_dentry(struct dentry *dentry)
32{
33 spin_lock(&dentry->d_lock);
34 dentry->d_flags |= DCACHE_ENCRYPTED_WITH_KEY;
35 spin_unlock(&dentry->d_lock);
36}
37
38/* policy.c */
39extern int fscrypt_ioctl_set_policy(struct file *, const void __user *);
40extern int fscrypt_ioctl_get_policy(struct file *, void __user *);
41extern int fscrypt_has_permitted_context(struct inode *, struct inode *);
42extern int fscrypt_inherit_context(struct inode *, struct inode *,
43 void *, bool);
44/* keyinfo.c */
45extern int fscrypt_get_encryption_info(struct inode *);
46extern void fscrypt_put_encryption_info(struct inode *, struct fscrypt_info *);
47
48/* fname.c */
49extern int fscrypt_setup_filename(struct inode *, const struct qstr *,
50 int lookup, struct fscrypt_name *);
51
52static inline void fscrypt_free_filename(struct fscrypt_name *fname)
53{
54 kfree(fname->crypto_buf.name);
55}
56
57extern u32 fscrypt_fname_encrypted_size(const struct inode *, u32);
58extern int fscrypt_fname_alloc_buffer(const struct inode *, u32,
59 struct fscrypt_str *);
60extern void fscrypt_fname_free_buffer(struct fscrypt_str *);
61extern int fscrypt_fname_disk_to_usr(struct inode *, u32, u32,
62 const struct fscrypt_str *, struct fscrypt_str *);
63extern int fscrypt_fname_usr_to_disk(struct inode *, const struct qstr *,
64 struct fscrypt_str *);
65
66#define FSCRYPT_FNAME_MAX_UNDIGESTED_SIZE 32
67
68/* Extracts the second-to-last ciphertext block; see explanation below */
69#define FSCRYPT_FNAME_DIGEST(name, len) \
70 ((name) + round_down((len) - FS_CRYPTO_BLOCK_SIZE - 1, \
71 FS_CRYPTO_BLOCK_SIZE))
72
73#define FSCRYPT_FNAME_DIGEST_SIZE FS_CRYPTO_BLOCK_SIZE
74
75/**
76 * fscrypt_digested_name - alternate identifier for an on-disk filename
77 *
78 * When userspace lists an encrypted directory without access to the key,
79 * filenames whose ciphertext is longer than FSCRYPT_FNAME_MAX_UNDIGESTED_SIZE
80 * bytes are shown in this abbreviated form (base64-encoded) rather than as the
81 * full ciphertext (base64-encoded). This is necessary to allow supporting
82 * filenames up to NAME_MAX bytes, since base64 encoding expands the length.
83 *
84 * To make it possible for filesystems to still find the correct directory entry
85 * despite not knowing the full on-disk name, we encode any filesystem-specific
86 * 'hash' and/or 'minor_hash' which the filesystem may need for its lookups,
87 * followed by the second-to-last ciphertext block of the filename. Due to the
88 * use of the CBC-CTS encryption mode, the second-to-last ciphertext block
89 * depends on the full plaintext. (Note that ciphertext stealing causes the
90 * last two blocks to appear "flipped".) This makes accidental collisions very
91 * unlikely: just a 1 in 2^128 chance for two filenames to collide even if they
92 * share the same filesystem-specific hashes.
93 *
94 * However, this scheme isn't immune to intentional collisions, which can be
95 * created by anyone able to create arbitrary plaintext filenames and view them
96 * without the key. Making the "digest" be a real cryptographic hash like
97 * SHA-256 over the full ciphertext would prevent this, although it would be
98 * less efficient and harder to implement, especially since the filesystem would
99 * need to calculate it for each directory entry examined during a search.
100 */
101struct fscrypt_digested_name {
102 u32 hash;
103 u32 minor_hash;
104 u8 digest[FSCRYPT_FNAME_DIGEST_SIZE];
105};
106
107/**
108 * fscrypt_match_name() - test whether the given name matches a directory entry
109 * @fname: the name being searched for
110 * @de_name: the name from the directory entry
111 * @de_name_len: the length of @de_name in bytes
112 *
113 * Normally @fname->disk_name will be set, and in that case we simply compare
114 * that to the name stored in the directory entry. The only exception is that
115 * if we don't have the key for an encrypted directory and a filename in it is
116 * very long, then we won't have the full disk_name and we'll instead need to
117 * match against the fscrypt_digested_name.
118 *
119 * Return: %true if the name matches, otherwise %false.
120 */
121static inline bool fscrypt_match_name(const struct fscrypt_name *fname,
122 const u8 *de_name, u32 de_name_len)
123{
124 if (unlikely(!fname->disk_name.name)) {
125 const struct fscrypt_digested_name *n =
126 (const void *)fname->crypto_buf.name;
127 if (WARN_ON_ONCE(fname->usr_fname->name[0] != '_'))
128 return false;
129 if (de_name_len <= FSCRYPT_FNAME_MAX_UNDIGESTED_SIZE)
130 return false;
131 return !memcmp(FSCRYPT_FNAME_DIGEST(de_name, de_name_len),
132 n->digest, FSCRYPT_FNAME_DIGEST_SIZE);
133 }
134
135 if (de_name_len != fname->disk_name.len)
136 return false;
137 return !memcmp(de_name, fname->disk_name.name, fname->disk_name.len);
138}
139
140/* bio.c */
141extern void fscrypt_decrypt_bio_pages(struct fscrypt_ctx *, struct bio *);
142extern void fscrypt_pullback_bio_page(struct page **, bool);
143extern int fscrypt_zeroout_range(const struct inode *, pgoff_t, sector_t,
144 unsigned int);
145
146#endif /* _LINUX_FSCRYPT_SUPP_H */