include/linux/fscrypt_supp.h

   1 /* SPDX-License-Identifier: GPL-2.0 */
   2 /*
   3  * fscrypt_supp.h
   4  *
   5  * Do not include this file directly. Use fscrypt.h instead!
   6  */
   7 #ifndef _LINUX_FSCRYPT_H
   8 #error "Incorrect include of linux/fscrypt_supp.h!"
   9 #endif
  10
  11 #ifndef _LINUX_FSCRYPT_SUPP_H
  12 #define _LINUX_FSCRYPT_SUPP_H
  13
  14 #include <linux/mm.h>
  15 #include <linux/slab.h>
  16
  17 /*
  18  * fscrypt superblock flags
  19  */
  20 #define FS_CFLG_OWN_PAGES (1U << 1)
  21
  22 /*
  23  * crypto operations for filesystems
  24  */
  25 struct fscrypt_operations {
  26         unsigned int flags;
  27         const char *key_prefix;
  28         int (*get_context)(struct inode *, void *, size_t);
  29         int (*set_context)(struct inode *, const void *, size_t, void *);
  30         bool (*dummy_context)(struct inode *);
  31         bool (*empty_dir)(struct inode *);
  32         unsigned (*max_namelen)(struct inode *);
  33 };
  34
  35 struct fscrypt_ctx {
  36         union {
  37                 struct {
  38                         struct page *bounce_page;       /* Ciphertext page */
  39                         struct page *control_page;      /* Original page  */
  40                 } w;
  41                 struct {
  42                         struct bio *bio;
  43                         struct work_struct work;
  44                 } r;
  45                 struct list_head free_list;     /* Free list */
  46         };
  47         u8 flags;                               /* Flags */
  48 };
  49
  50 static inline bool fscrypt_has_encryption_key(const struct inode *inode)
  51 {
  52         return (inode->i_crypt_info != NULL);
  53 }
  54
  55 static inline bool fscrypt_dummy_context_enabled(struct inode *inode)
  56 {
  57         return inode->i_sb->s_cop->dummy_context &&
  58                 inode->i_sb->s_cop->dummy_context(inode);
  59 }
  60
  61 /* crypto.c */
  62 extern struct fscrypt_ctx *fscrypt_get_ctx(const struct inode *, gfp_t);
  63 extern void fscrypt_release_ctx(struct fscrypt_ctx *);
  64 extern struct page *fscrypt_encrypt_page(const struct inode *, struct page *,
  65                                                 unsigned int, unsigned int,
  66                                                 u64, gfp_t);
  67 extern int fscrypt_decrypt_page(const struct inode *, struct page *, unsigned int,
  68                                 unsigned int, u64);
  69
  70 static inline struct page *fscrypt_control_page(struct page *page)
  71 {
  72         return ((struct fscrypt_ctx *)page_private(page))->w.control_page;
  73 }
  74
  75 extern void fscrypt_restore_control_page(struct page *);
  76
  77 extern const struct dentry_operations fscrypt_d_ops;
  78
  79 static inline void fscrypt_set_d_op(struct dentry *dentry)
  80 {
  81         d_set_d_op(dentry, &fscrypt_d_ops);
  82 }
  83
  84 static inline void fscrypt_set_encrypted_dentry(struct dentry *dentry)
  85 {
  86         spin_lock(&dentry->d_lock);
  87         dentry->d_flags |= DCACHE_ENCRYPTED_WITH_KEY;
  88         spin_unlock(&dentry->d_lock);
  89 }
  90
  91 /* policy.c */
  92 extern int fscrypt_ioctl_set_policy(struct file *, const void __user *);
  93 extern int fscrypt_ioctl_get_policy(struct file *, void __user *);
  94 extern int fscrypt_has_permitted_context(struct inode *, struct inode *);
  95 extern int fscrypt_inherit_context(struct inode *, struct inode *,
  96                                         void *, bool);
  97 /* keyinfo.c */
  98 extern int fscrypt_get_encryption_info(struct inode *);
  99 extern void fscrypt_put_encryption_info(struct inode *);
 100
 101 /* fname.c */
 102 extern int fscrypt_setup_filename(struct inode *, const struct qstr *,
 103                                 int lookup, struct fscrypt_name *);
 104
 105 static inline void fscrypt_free_filename(struct fscrypt_name *fname)
 106 {
 107         kfree(fname->crypto_buf.name);
 108 }
 109
 110 extern int fscrypt_fname_alloc_buffer(const struct inode *, u32,
 111                                 struct fscrypt_str *);
 112 extern void fscrypt_fname_free_buffer(struct fscrypt_str *);
 113 extern int fscrypt_fname_disk_to_usr(struct inode *, u32, u32,
 114                         const struct fscrypt_str *, struct fscrypt_str *);
 115
 116 #define FSCRYPT_FNAME_MAX_UNDIGESTED_SIZE       32
 117
 118 /* Extracts the second-to-last ciphertext block; see explanation below */
 119 #define FSCRYPT_FNAME_DIGEST(name, len) \
 120         ((name) + round_down((len) - FS_CRYPTO_BLOCK_SIZE - 1, \
 121                              FS_CRYPTO_BLOCK_SIZE))
 122
 123 #define FSCRYPT_FNAME_DIGEST_SIZE       FS_CRYPTO_BLOCK_SIZE
 124
 125 /**
 126  * fscrypt_digested_name - alternate identifier for an on-disk filename
 127  *
 128  * When userspace lists an encrypted directory without access to the key,
 129  * filenames whose ciphertext is longer than FSCRYPT_FNAME_MAX_UNDIGESTED_SIZE
 130  * bytes are shown in this abbreviated form (base64-encoded) rather than as the
 131  * full ciphertext (base64-encoded).  This is necessary to allow supporting
 132  * filenames up to NAME_MAX bytes, since base64 encoding expands the length.
 133  *
 134  * To make it possible for filesystems to still find the correct directory entry
 135  * despite not knowing the full on-disk name, we encode any filesystem-specific
 136  * 'hash' and/or 'minor_hash' which the filesystem may need for its lookups,
 137  * followed by the second-to-last ciphertext block of the filename.  Due to the
 138  * use of the CBC-CTS encryption mode, the second-to-last ciphertext block
 139  * depends on the full plaintext.  (Note that ciphertext stealing causes the
 140  * last two blocks to appear "flipped".)  This makes accidental collisions very
 141  * unlikely: just a 1 in 2^128 chance for two filenames to collide even if they
 142  * share the same filesystem-specific hashes.
 143  *
 144  * However, this scheme isn't immune to intentional collisions, which can be
 145  * created by anyone able to create arbitrary plaintext filenames and view them
 146  * without the key.  Making the "digest" be a real cryptographic hash like
 147  * SHA-256 over the full ciphertext would prevent this, although it would be
 148  * less efficient and harder to implement, especially since the filesystem would
 149  * need to calculate it for each directory entry examined during a search.
 150  */
 151 struct fscrypt_digested_name {
 152         u32 hash;
 153         u32 minor_hash;
 154         u8 digest[FSCRYPT_FNAME_DIGEST_SIZE];
 155 };
 156
 157 /**
 158  * fscrypt_match_name() - test whether the given name matches a directory entry
 159  * @fname: the name being searched for
 160  * @de_name: the name from the directory entry
 161  * @de_name_len: the length of @de_name in bytes
 162  *
 163  * Normally @fname->disk_name will be set, and in that case we simply compare
 164  * that to the name stored in the directory entry.  The only exception is that
 165  * if we don't have the key for an encrypted directory and a filename in it is
 166  * very long, then we won't have the full disk_name and we'll instead need to
 167  * match against the fscrypt_digested_name.
 168  *
 169  * Return: %true if the name matches, otherwise %false.
 170  */
 171 static inline bool fscrypt_match_name(const struct fscrypt_name *fname,
 172                                       const u8 *de_name, u32 de_name_len)
 173 {
 174         if (unlikely(!fname->disk_name.name)) {
 175                 const struct fscrypt_digested_name *n =
 176                         (const void *)fname->crypto_buf.name;
 177                 if (WARN_ON_ONCE(fname->usr_fname->name[0] != '_'))
 178                         return false;
 179                 if (de_name_len <= FSCRYPT_FNAME_MAX_UNDIGESTED_SIZE)
 180                         return false;
 181                 return !memcmp(FSCRYPT_FNAME_DIGEST(de_name, de_name_len),
 182                                n->digest, FSCRYPT_FNAME_DIGEST_SIZE);
 183         }
 184
 185         if (de_name_len != fname->disk_name.len)
 186                 return false;
 187         return !memcmp(de_name, fname->disk_name.name, fname->disk_name.len);
 188 }
 189
 190 /* bio.c */
 191 extern void fscrypt_decrypt_bio_pages(struct fscrypt_ctx *, struct bio *);
 192 extern void fscrypt_pullback_bio_page(struct page **, bool);
 193 extern int fscrypt_zeroout_range(const struct inode *, pgoff_t, sector_t,
 194                                  unsigned int);
 195
 196 /* hooks.c */
 197 extern int fscrypt_file_open(struct inode *inode, struct file *filp);
 198 extern int __fscrypt_prepare_link(struct inode *inode, struct inode *dir);
 199 extern int __fscrypt_prepare_rename(struct inode *old_dir,
 200                                     struct dentry *old_dentry,
 201                                     struct inode *new_dir,
 202                                     struct dentry *new_dentry,
 203                                     unsigned int flags);
 204 extern int __fscrypt_prepare_lookup(struct inode *dir, struct dentry *dentry);
 205 extern int __fscrypt_prepare_symlink(struct inode *dir, unsigned int len,
 206                                      unsigned int max_len,
 207                                      struct fscrypt_str *disk_link);
 208 extern int __fscrypt_encrypt_symlink(struct inode *inode, const char *target,
 209                                      unsigned int len,
 210                                      struct fscrypt_str *disk_link);
 211 extern const char *fscrypt_get_symlink(struct inode *inode, const void *caddr,
 212                                        unsigned int max_size,
 213                                        struct delayed_call *done);
 214
 215 #endif  /* _LINUX_FSCRYPT_SUPP_H */