include/linux/fscrypt_supp.h

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