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 /* crypto.c */
  15 extern struct kmem_cache *fscrypt_info_cachep;
  16 extern struct fscrypt_ctx *fscrypt_get_ctx(const struct inode *, gfp_t);
  17 extern void fscrypt_release_ctx(struct fscrypt_ctx *);
  18 extern struct page *fscrypt_encrypt_page(const struct inode *, struct page *,
  19                                                 unsigned int, unsigned int,
  20                                                 u64, gfp_t);
  21 extern int fscrypt_decrypt_page(const struct inode *, struct page *, unsigned int,
  22                                 unsigned int, u64);
  23 extern void fscrypt_restore_control_page(struct page *);
  24
  25 extern const struct dentry_operations fscrypt_d_ops;
  26
  27 static inline void fscrypt_set_d_op(struct dentry *dentry)
  28 {
  29         d_set_d_op(dentry, &fscrypt_d_ops);
  30 }
  31
  32 static inline void fscrypt_set_encrypted_dentry(struct dentry *dentry)
  33 {
  34         spin_lock(&dentry->d_lock);
  35         dentry->d_flags |= DCACHE_ENCRYPTED_WITH_KEY;
  36         spin_unlock(&dentry->d_lock);
  37 }
  38
  39 /* policy.c */
  40 extern int fscrypt_ioctl_set_policy(struct file *, const void __user *);
  41 extern int fscrypt_ioctl_get_policy(struct file *, void __user *);
  42 extern int fscrypt_has_permitted_context(struct inode *, struct inode *);
  43 extern int fscrypt_inherit_context(struct inode *, struct inode *,
  44                                         void *, bool);
  45 /* keyinfo.c */
  46 extern int fscrypt_get_encryption_info(struct inode *);
  47 extern void fscrypt_put_encryption_info(struct inode *, struct fscrypt_info *);
  48
  49 /* fname.c */
  50 extern int fscrypt_setup_filename(struct inode *, const struct qstr *,
  51                                 int lookup, struct fscrypt_name *);
  52
  53 static inline void fscrypt_free_filename(struct fscrypt_name *fname)
  54 {
  55         kfree(fname->crypto_buf.name);
  56 }
  57
  58 extern u32 fscrypt_fname_encrypted_size(const struct inode *, u32);
  59 extern int fscrypt_fname_alloc_buffer(const struct inode *, u32,
  60                                 struct fscrypt_str *);
  61 extern void fscrypt_fname_free_buffer(struct fscrypt_str *);
  62 extern int fscrypt_fname_disk_to_usr(struct inode *, u32, u32,
  63                         const struct fscrypt_str *, struct fscrypt_str *);
  64 extern int fscrypt_fname_usr_to_disk(struct inode *, const struct qstr *,
  65                         struct fscrypt_str *);
  66
  67 #define FSCRYPT_FNAME_MAX_UNDIGESTED_SIZE       32
  68
  69 /* Extracts the second-to-last ciphertext block; see explanation below */
  70 #define FSCRYPT_FNAME_DIGEST(name, len) \
  71         ((name) + round_down((len) - FS_CRYPTO_BLOCK_SIZE - 1, \
  72                              FS_CRYPTO_BLOCK_SIZE))
  73
  74 #define FSCRYPT_FNAME_DIGEST_SIZE       FS_CRYPTO_BLOCK_SIZE
  75
  76 /**
  77  * fscrypt_digested_name - alternate identifier for an on-disk filename
  78  *
  79  * When userspace lists an encrypted directory without access to the key,
  80  * filenames whose ciphertext is longer than FSCRYPT_FNAME_MAX_UNDIGESTED_SIZE
  81  * bytes are shown in this abbreviated form (base64-encoded) rather than as the
  82  * full ciphertext (base64-encoded).  This is necessary to allow supporting
  83  * filenames up to NAME_MAX bytes, since base64 encoding expands the length.
  84  *
  85  * To make it possible for filesystems to still find the correct directory entry
  86  * despite not knowing the full on-disk name, we encode any filesystem-specific
  87  * 'hash' and/or 'minor_hash' which the filesystem may need for its lookups,
  88  * followed by the second-to-last ciphertext block of the filename.  Due to the
  89  * use of the CBC-CTS encryption mode, the second-to-last ciphertext block
  90  * depends on the full plaintext.  (Note that ciphertext stealing causes the
  91  * last two blocks to appear "flipped".)  This makes accidental collisions very
  92  * unlikely: just a 1 in 2^128 chance for two filenames to collide even if they
  93  * share the same filesystem-specific hashes.
  94  *
  95  * However, this scheme isn't immune to intentional collisions, which can be
  96  * created by anyone able to create arbitrary plaintext filenames and view them
  97  * without the key.  Making the "digest" be a real cryptographic hash like
  98  * SHA-256 over the full ciphertext would prevent this, although it would be
  99  * less efficient and harder to implement, especially since the filesystem would
 100  * need to calculate it for each directory entry examined during a search.
 101  */
 102 struct fscrypt_digested_name {
 103         u32 hash;
 104         u32 minor_hash;
 105         u8 digest[FSCRYPT_FNAME_DIGEST_SIZE];
 106 };
 107
 108 /**
 109  * fscrypt_match_name() - test whether the given name matches a directory entry
 110  * @fname: the name being searched for
 111  * @de_name: the name from the directory entry
 112  * @de_name_len: the length of @de_name in bytes
 113  *
 114  * Normally @fname->disk_name will be set, and in that case we simply compare
 115  * that to the name stored in the directory entry.  The only exception is that
 116  * if we don't have the key for an encrypted directory and a filename in it is
 117  * very long, then we won't have the full disk_name and we'll instead need to
 118  * match against the fscrypt_digested_name.
 119  *
 120  * Return: %true if the name matches, otherwise %false.
 121  */
 122 static inline bool fscrypt_match_name(const struct fscrypt_name *fname,
 123                                       const u8 *de_name, u32 de_name_len)
 124 {
 125         if (unlikely(!fname->disk_name.name)) {
 126                 const struct fscrypt_digested_name *n =
 127                         (const void *)fname->crypto_buf.name;
 128                 if (WARN_ON_ONCE(fname->usr_fname->name[0] != '_'))
 129                         return false;
 130                 if (de_name_len <= FSCRYPT_FNAME_MAX_UNDIGESTED_SIZE)
 131                         return false;
 132                 return !memcmp(FSCRYPT_FNAME_DIGEST(de_name, de_name_len),
 133                                n->digest, FSCRYPT_FNAME_DIGEST_SIZE);
 134         }
 135
 136         if (de_name_len != fname->disk_name.len)
 137                 return false;
 138         return !memcmp(de_name, fname->disk_name.name, fname->disk_name.len);
 139 }
 140
 141 /* bio.c */
 142 extern void fscrypt_decrypt_bio_pages(struct fscrypt_ctx *, struct bio *);
 143 extern void fscrypt_pullback_bio_page(struct page **, bool);
 144 extern int fscrypt_zeroout_range(const struct inode *, pgoff_t, sector_t,
 145                                  unsigned int);
 146
 147 /* hooks.c */
 148 extern int fscrypt_file_open(struct inode *inode, struct file *filp);
 149 extern int __fscrypt_prepare_link(struct inode *inode, struct inode *dir);
 150 extern int __fscrypt_prepare_rename(struct inode *old_dir,
 151                                     struct dentry *old_dentry,
 152                                     struct inode *new_dir,
 153                                     struct dentry *new_dentry,
 154                                     unsigned int flags);
 155 extern int __fscrypt_prepare_lookup(struct inode *dir, struct dentry *dentry);
 156
 157 #endif  /* _LINUX_FSCRYPT_SUPP_H */