From 40c60e1610b63c7499b2df6df79547d691a0c72f Mon Sep 17 00:00:00 2001 From: Eric Biggers Date: Wed, 3 Jan 2018 11:16:27 -0800 Subject: crypto: hash - prevent using keyed hashes without setting key Currently, almost none of the keyed hash algorithms check whether a key has been set before proceeding. Some algorithms are okay with this and will effectively just use a key of all 0's or some other bogus default. However, others will severely break, as demonstrated using "hmac(sha3-512-generic)", the unkeyed use of which causes a kernel crash via a (potentially exploitable) stack buffer overflow. A while ago, this problem was solved for AF_ALG by pairing each hash transform with a 'has_key' bool. However, there are still other places in the kernel where userspace can specify an arbitrary hash algorithm by name, and the kernel uses it as unkeyed hash without checking whether it is really unkeyed. Examples of this include: - KEYCTL_DH_COMPUTE, via the KDF extension - dm-verity - dm-crypt, via the ESSIV support - dm-integrity, via the "internal hash" mode with no key given - drbd (Distributed Replicated Block Device) This bug is especially bad for KEYCTL_DH_COMPUTE as that requires no privileges to call. Fix the bug for all users by adding a flag CRYPTO_TFM_NEED_KEY to the ->crt_flags of each hash transform that indicates whether the transform still needs to be keyed or not. Then, make the hash init, import, and digest functions return -ENOKEY if the key is still needed. The new flag also replaces the 'has_key' bool which algif_hash was previously using, thereby simplifying the algif_hash implementation. Reported-by: syzbot Cc: stable@vger.kernel.org Signed-off-by: Eric Biggers Signed-off-by: Herbert Xu --- crypto/shash.c | 25 +++++++++++++++++++++---- 1 file changed, 21 insertions(+), 4 deletions(-) (limited to 'crypto/shash.c') diff --git a/crypto/shash.c b/crypto/shash.c index e849d3ee..5d732c6b 100644 --- a/crypto/shash.c +++ b/crypto/shash.c @@ -58,11 +58,18 @@ int crypto_shash_setkey(struct crypto_shash *tfm, const u8 *key, { struct shash_alg *shash = crypto_shash_alg(tfm); unsigned long alignmask = crypto_shash_alignmask(tfm); + int err; if ((unsigned long)key & alignmask) - return shash_setkey_unaligned(tfm, key, keylen); + err = shash_setkey_unaligned(tfm, key, keylen); + else + err = shash->setkey(tfm, key, keylen); + + if (err) + return err; - return shash->setkey(tfm, key, keylen); + crypto_shash_clear_flags(tfm, CRYPTO_TFM_NEED_KEY); + return 0; } EXPORT_SYMBOL_GPL(crypto_shash_setkey); @@ -181,6 +188,9 @@ int crypto_shash_digest(struct shash_desc *desc, const u8 *data, struct shash_alg *shash = crypto_shash_alg(tfm); unsigned long alignmask = crypto_shash_alignmask(tfm); + if (crypto_shash_get_flags(tfm) & CRYPTO_TFM_NEED_KEY) + return -ENOKEY; + if (((unsigned long)data | (unsigned long)out) & alignmask) return shash_digest_unaligned(desc, data, len, out); @@ -360,7 +370,8 @@ int crypto_init_shash_ops_async(struct crypto_tfm *tfm) crt->digest = shash_async_digest; crt->setkey = shash_async_setkey; - crt->has_setkey = alg->setkey != shash_no_setkey; + crypto_ahash_set_flags(crt, crypto_shash_get_flags(shash) & + CRYPTO_TFM_NEED_KEY); if (alg->export) crt->export = shash_async_export; @@ -375,8 +386,14 @@ int crypto_init_shash_ops_async(struct crypto_tfm *tfm) static int crypto_shash_init_tfm(struct crypto_tfm *tfm) { struct crypto_shash *hash = __crypto_shash_cast(tfm); + struct shash_alg *alg = crypto_shash_alg(hash); + + hash->descsize = alg->descsize; + + if (crypto_shash_alg_has_setkey(alg) && + !(alg->base.cra_flags & CRYPTO_ALG_OPTIONAL_KEY)) + crypto_shash_set_flags(hash, CRYPTO_TFM_NEED_KEY); - hash->descsize = crypto_shash_alg(hash)->descsize; return 0; } -- cgit v1.2.3