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 int max_namelen;
  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 void fscrypt_enqueue_decrypt_work(struct work_struct *);
  63 extern struct fscrypt_ctx *fscrypt_get_ctx(const struct inode *, gfp_t);
  64 extern void fscrypt_release_ctx(struct fscrypt_ctx *);
  65 extern struct page *fscrypt_encrypt_page(const struct inode *, struct page *,
  66                                                 unsigned int, unsigned int,
  67                                                 u64, gfp_t);
  68 extern int fscrypt_decrypt_page(const struct inode *, struct page *, unsigned int,
  69                                 unsigned int, u64);
  70
  71 static inline struct page *fscrypt_control_page(struct page *page)
  72 {
  73         return ((struct fscrypt_ctx *)page_private(page))->w.control_page;
  74 }
  75
  76 extern void fscrypt_restore_control_page(struct page *);
  77
  78 /* policy.c */
  79 extern int fscrypt_ioctl_set_policy(struct file *, const void __user *);
  80 extern int fscrypt_ioctl_get_policy(struct file *, void __user *);
  81 extern int fscrypt_has_permitted_context(struct inode *, struct inode *);
  82 extern int fscrypt_inherit_context(struct inode *, struct inode *,
  83                                         void *, bool);
  84 /* keyinfo.c */
  85 extern int fscrypt_get_encryption_info(struct inode *);
  86 extern void fscrypt_put_encryption_info(struct inode *);
  87
  88 /* fname.c */
  89 extern int fscrypt_setup_filename(struct inode *, const struct qstr *,
  90                                 int lookup, struct fscrypt_name *);
  91
  92 static inline void fscrypt_free_filename(struct fscrypt_name *fname)
  93 {
  94         kfree(fname->crypto_buf.name);
  95 }
  96
  97 extern int fscrypt_fname_alloc_buffer(const struct inode *, u32,
  98                                 struct fscrypt_str *);
  99 extern void fscrypt_fname_free_buffer(struct fscrypt_str *);
 100 extern int fscrypt_fname_disk_to_usr(struct inode *, u32, u32,
 101                         const struct fscrypt_str *, struct fscrypt_str *);
 102
 103 #define FSCRYPT_FNAME_MAX_UNDIGESTED_SIZE       32
 104
 105 /* Extracts the second-to-last ciphertext block; see explanation below */
 106 #define FSCRYPT_FNAME_DIGEST(name, len) \
 107         ((name) + round_down((len) - FS_CRYPTO_BLOCK_SIZE - 1, \
 108                              FS_CRYPTO_BLOCK_SIZE))
 109
 110 #define FSCRYPT_FNAME_DIGEST_SIZE       FS_CRYPTO_BLOCK_SIZE
 111
 112 /**
 113  * fscrypt_digested_name - alternate identifier for an on-disk filename
 114  *
 115  * When userspace lists an encrypted directory without access to the key,
 116  * filenames whose ciphertext is longer than FSCRYPT_FNAME_MAX_UNDIGESTED_SIZE
 117  * bytes are shown in this abbreviated form (base64-encoded) rather than as the
 118  * full ciphertext (base64-encoded).  This is necessary to allow supporting
 119  * filenames up to NAME_MAX bytes, since base64 encoding expands the length.
 120  *
 121  * To make it possible for filesystems to still find the correct directory entry
 122  * despite not knowing the full on-disk name, we encode any filesystem-specific
 123  * 'hash' and/or 'minor_hash' which the filesystem may need for its lookups,
 124  * followed by the second-to-last ciphertext block of the filename.  Due to the
 125  * use of the CBC-CTS encryption mode, the second-to-last ciphertext block
 126  * depends on the full plaintext.  (Note that ciphertext stealing causes the
 127  * last two blocks to appear "flipped".)  This makes accidental collisions very
 128  * unlikely: just a 1 in 2^128 chance for two filenames to collide even if they
 129  * share the same filesystem-specific hashes.
 130  *
 131  * However, this scheme isn't immune to intentional collisions, which can be
 132  * created by anyone able to create arbitrary plaintext filenames and view them
 133  * without the key.  Making the "digest" be a real cryptographic hash like
 134  * SHA-256 over the full ciphertext would prevent this, although it would be
 135  * less efficient and harder to implement, especially since the filesystem would
 136  * need to calculate it for each directory entry examined during a search.
 137  */
 138 struct fscrypt_digested_name {
 139         u32 hash;
 140         u32 minor_hash;
 141         u8 digest[FSCRYPT_FNAME_DIGEST_SIZE];
 142 };
 143
 144 /**
 145  * fscrypt_match_name() - test whether the given name matches a directory entry
 146  * @fname: the name being searched for
 147  * @de_name: the name from the directory entry
 148  * @de_name_len: the length of @de_name in bytes
 149  *
 150  * Normally @fname->disk_name will be set, and in that case we simply compare
 151  * that to the name stored in the directory entry.  The only exception is that
 152  * if we don't have the key for an encrypted directory and a filename in it is
 153  * very long, then we won't have the full disk_name and we'll instead need to
 154  * match against the fscrypt_digested_name.
 155  *
 156  * Return: %true if the name matches, otherwise %false.
 157  */
 158 static inline bool fscrypt_match_name(const struct fscrypt_name *fname,
 159                                       const u8 *de_name, u32 de_name_len)
 160 {
 161         if (unlikely(!fname->disk_name.name)) {
 162                 const struct fscrypt_digested_name *n =
 163                         (const void *)fname->crypto_buf.name;
 164                 if (WARN_ON_ONCE(fname->usr_fname->name[0] != '_'))
 165                         return false;
 166                 if (de_name_len <= FSCRYPT_FNAME_MAX_UNDIGESTED_SIZE)
 167                         return false;
 168                 return !memcmp(FSCRYPT_FNAME_DIGEST(de_name, de_name_len),
 169                                n->digest, FSCRYPT_FNAME_DIGEST_SIZE);
 170         }
 171
 172         if (de_name_len != fname->disk_name.len)
 173                 return false;
 174         return !memcmp(de_name, fname->disk_name.name, fname->disk_name.len);
 175 }
 176
 177 /* bio.c */
 178 extern void fscrypt_decrypt_bio(struct bio *);
 179 extern void fscrypt_enqueue_decrypt_bio(struct fscrypt_ctx *ctx,
 180                                         struct bio *bio);
 181 extern void fscrypt_pullback_bio_page(struct page **, bool);
 182 extern int fscrypt_zeroout_range(const struct inode *, pgoff_t, sector_t,
 183                                  unsigned int);
 184
 185 /* hooks.c */
 186 extern int fscrypt_file_open(struct inode *inode, struct file *filp);
 187 extern int __fscrypt_prepare_link(struct inode *inode, struct inode *dir);
 188 extern int __fscrypt_prepare_rename(struct inode *old_dir,
 189                                     struct dentry *old_dentry,
 190                                     struct inode *new_dir,
 191                                     struct dentry *new_dentry,
 192                                     unsigned int flags);
 193 extern int __fscrypt_prepare_lookup(struct inode *dir, struct dentry *dentry);
 194 extern int __fscrypt_prepare_symlink(struct inode *dir, unsigned int len,
 195                                      unsigned int max_len,
 196                                      struct fscrypt_str *disk_link);
 197 extern int __fscrypt_encrypt_symlink(struct inode *inode, const char *target,
 198                                      unsigned int len,
 199                                      struct fscrypt_str *disk_link);
 200 extern const char *fscrypt_get_symlink(struct inode *inode, const void *caddr,
 201                                        unsigned int max_size,
 202                                        struct delayed_call *done);
 203
 204 #endif  /* _LINUX_FSCRYPT_SUPP_H */