diff options
Diffstat (limited to 'fs/crypto/keysetup.c')
| -rw-r--r-- | fs/crypto/keysetup.c | 57 |
1 files changed, 45 insertions, 12 deletions
diff --git a/fs/crypto/keysetup.c b/fs/crypto/keysetup.c index bca9c6658a7c..89cd533a88bf 100644 --- a/fs/crypto/keysetup.c +++ b/fs/crypto/keysetup.c @@ -19,6 +19,7 @@ struct fscrypt_mode fscrypt_modes[] = { .friendly_name = "AES-256-XTS", .cipher_str = "xts(aes)", .keysize = 64, + .security_strength = 32, .ivsize = 16, .blk_crypto_mode = BLK_ENCRYPTION_MODE_AES_256_XTS, }, @@ -26,12 +27,14 @@ struct fscrypt_mode fscrypt_modes[] = { .friendly_name = "AES-256-CTS-CBC", .cipher_str = "cts(cbc(aes))", .keysize = 32, + .security_strength = 32, .ivsize = 16, }, [FSCRYPT_MODE_AES_128_CBC] = { .friendly_name = "AES-128-CBC-ESSIV", .cipher_str = "essiv(cbc(aes),sha256)", .keysize = 16, + .security_strength = 16, .ivsize = 16, .blk_crypto_mode = BLK_ENCRYPTION_MODE_AES_128_CBC_ESSIV, }, @@ -39,12 +42,14 @@ struct fscrypt_mode fscrypt_modes[] = { .friendly_name = "AES-128-CTS-CBC", .cipher_str = "cts(cbc(aes))", .keysize = 16, + .security_strength = 16, .ivsize = 16, }, [FSCRYPT_MODE_ADIANTUM] = { .friendly_name = "Adiantum", .cipher_str = "adiantum(xchacha12,aes)", .keysize = 32, + .security_strength = 32, .ivsize = 32, .blk_crypto_mode = BLK_ENCRYPTION_MODE_ADIANTUM, }, @@ -358,6 +363,45 @@ static int fscrypt_setup_v2_file_key(struct fscrypt_info *ci, } /* + * Check whether the size of the given master key (@mk) is appropriate for the + * encryption settings which a particular file will use (@ci). + * + * If the file uses a v1 encryption policy, then the master key must be at least + * as long as the derived key, as this is a requirement of the v1 KDF. + * + * Otherwise, the KDF can accept any size key, so we enforce a slightly looser + * requirement: we require that the size of the master key be at least the + * maximum security strength of any algorithm whose key will be derived from it + * (but in practice we only need to consider @ci->ci_mode, since any other + * possible subkeys such as DIRHASH and INODE_HASH will never increase the + * required key size over @ci->ci_mode). This allows AES-256-XTS keys to be + * derived from a 256-bit master key, which is cryptographically sufficient, + * rather than requiring a 512-bit master key which is unnecessarily long. (We + * still allow 512-bit master keys if the user chooses to use them, though.) + */ +static bool fscrypt_valid_master_key_size(const struct fscrypt_master_key *mk, + const struct fscrypt_info *ci) +{ + unsigned int min_keysize; + + if (ci->ci_policy.version == FSCRYPT_POLICY_V1) + min_keysize = ci->ci_mode->keysize; + else + min_keysize = ci->ci_mode->security_strength; + + if (mk->mk_secret.size < min_keysize) { + fscrypt_warn(NULL, + "key with %s %*phN is too short (got %u bytes, need %u+ bytes)", + master_key_spec_type(&mk->mk_spec), + master_key_spec_len(&mk->mk_spec), + (u8 *)&mk->mk_spec.u, + mk->mk_secret.size, min_keysize); + return false; + } + return true; +} + +/* * Find the master key, then set up the inode's actual encryption key. * * If the master key is found in the filesystem-level keyring, then the @@ -422,18 +466,7 @@ static int setup_file_encryption_key(struct fscrypt_info *ci, goto out_release_key; } - /* - * Require that the master key be at least as long as the derived key. - * Otherwise, the derived key cannot possibly contain as much entropy as - * that required by the encryption mode it will be used for. For v1 - * policies it's also required for the KDF to work at all. - */ - if (mk->mk_secret.size < ci->ci_mode->keysize) { - fscrypt_warn(NULL, - "key with %s %*phN is too short (got %u bytes, need %u+ bytes)", - master_key_spec_type(&mk_spec), - master_key_spec_len(&mk_spec), (u8 *)&mk_spec.u, - mk->mk_secret.size, ci->ci_mode->keysize); + if (!fscrypt_valid_master_key_size(mk, ci)) { err = -ENOKEY; goto out_release_key; } |