From bd0d97b7191e8f3573681fa854fdb04c1a970c1e Mon Sep 17 00:00:00 2001 From: Eric Biggers Date: Tue, 21 Jul 2020 15:59:16 -0700 Subject: [PATCH] fscrypt: switch fscrypt_do_sha256() to use the SHA-256 library fscrypt_do_sha256() is only used for hashing encrypted filenames to create no-key tokens, which isn't performance-critical. Therefore a C implementation of SHA-256 is sufficient. Also, the logic to create no-key tokens is always potentially needed. This differs from fscrypt's other dependencies on crypto API algorithms, which are conditionally needed depending on what encryption policies userspace is using. Therefore, for fscrypt there isn't much benefit to allowing SHA-256 to be a loadable module. So, make fscrypt_do_sha256() use the SHA-256 library instead of the crypto_shash API. This is much simpler, since it avoids having to implement one-time-init (which is hard to do correctly, and in fact was implemented incorrectly) and handle failures to allocate the crypto_shash object. Fixes: edc440e3d27f ("fscrypt: improve format of no-key names") Cc: Daniel Rosenberg Link: https://lore.kernel.org/r/20200721225920.114347-2-ebiggers@kernel.org Signed-off-by: Eric Biggers --- fs/crypto/Kconfig | 2 +- fs/crypto/fname.c | 41 ++++++++++------------------------------- 2 files changed, 11 insertions(+), 32 deletions(-) diff --git a/fs/crypto/Kconfig b/fs/crypto/Kconfig index f1f11a6228eb..a5f5c30368a2 100644 --- a/fs/crypto/Kconfig +++ b/fs/crypto/Kconfig @@ -4,6 +4,7 @@ config FS_ENCRYPTION select CRYPTO select CRYPTO_HASH select CRYPTO_SKCIPHER + select CRYPTO_LIB_SHA256 select KEYS help Enable encryption of files and directories. This @@ -21,7 +22,6 @@ config FS_ENCRYPTION_ALGS select CRYPTO_CTS select CRYPTO_ECB select CRYPTO_HMAC - select CRYPTO_SHA256 select CRYPTO_SHA512 select CRYPTO_XTS diff --git a/fs/crypto/fname.c b/fs/crypto/fname.c index d828e3df898b..011830f84d8d 100644 --- a/fs/crypto/fname.c +++ b/fs/crypto/fname.c @@ -61,30 +61,13 @@ struct fscrypt_nokey_name { */ #define FSCRYPT_NOKEY_NAME_MAX offsetofend(struct fscrypt_nokey_name, sha256) -static struct crypto_shash *sha256_hash_tfm; - -static int fscrypt_do_sha256(const u8 *data, unsigned int data_len, u8 *result) +static void fscrypt_do_sha256(const u8 *data, unsigned int data_len, u8 *result) { - struct crypto_shash *tfm = READ_ONCE(sha256_hash_tfm); + struct sha256_state sctx; - if (unlikely(!tfm)) { - struct crypto_shash *prev_tfm; - - tfm = crypto_alloc_shash("sha256", 0, 0); - if (IS_ERR(tfm)) { - fscrypt_err(NULL, - "Error allocating SHA-256 transform: %ld", - PTR_ERR(tfm)); - return PTR_ERR(tfm); - } - prev_tfm = cmpxchg(&sha256_hash_tfm, NULL, tfm); - if (prev_tfm) { - crypto_free_shash(tfm); - tfm = prev_tfm; - } - } - - return crypto_shash_tfm_digest(tfm, data, data_len, result); + sha256_init(&sctx); + sha256_update(&sctx, data, data_len); + sha256_final(&sctx, result); } static inline bool fscrypt_is_dot_dotdot(const struct qstr *str) @@ -349,7 +332,6 @@ int fscrypt_fname_disk_to_usr(const struct inode *inode, const struct qstr qname = FSTR_TO_QSTR(iname); struct fscrypt_nokey_name nokey_name; u32 size; /* size of the unencoded no-key name */ - int err; if (fscrypt_is_dot_dotdot(&qname)) { oname->name[0] = '.'; @@ -387,11 +369,9 @@ int fscrypt_fname_disk_to_usr(const struct inode *inode, } else { memcpy(nokey_name.bytes, iname->name, sizeof(nokey_name.bytes)); /* Compute strong hash of remaining part of name. */ - err = fscrypt_do_sha256(&iname->name[sizeof(nokey_name.bytes)], - iname->len - sizeof(nokey_name.bytes), - nokey_name.sha256); - if (err) - return err; + fscrypt_do_sha256(&iname->name[sizeof(nokey_name.bytes)], + iname->len - sizeof(nokey_name.bytes), + nokey_name.sha256); size = FSCRYPT_NOKEY_NAME_MAX; } oname->len = base64_encode((const u8 *)&nokey_name, size, oname->name); @@ -530,9 +510,8 @@ bool fscrypt_match_name(const struct fscrypt_name *fname, return false; if (memcmp(de_name, nokey_name->bytes, sizeof(nokey_name->bytes))) return false; - if (fscrypt_do_sha256(&de_name[sizeof(nokey_name->bytes)], - de_name_len - sizeof(nokey_name->bytes), sha256)) - return false; + fscrypt_do_sha256(&de_name[sizeof(nokey_name->bytes)], + de_name_len - sizeof(nokey_name->bytes), sha256); return !memcmp(sha256, nokey_name->sha256, sizeof(sha256)); } EXPORT_SYMBOL_GPL(fscrypt_match_name);