crypto: hash - set CRYPTO_TFM_NEED_KEY if ->setkey() fails

Some algorithms have a ->setkey() method that is not atomic, in the
sense that setting a key can fail after changes were already made to the
tfm context.  In this case, if a key was already set the tfm can end up
in a state that corresponds to neither the old key nor the new key.

It's not feasible to make all ->setkey() methods atomic, especially ones
that have to key multiple sub-tfms.  Therefore, make the crypto API set
CRYPTO_TFM_NEED_KEY if ->setkey() fails and the algorithm requires a
key, to prevent the tfm from being used until a new key is set.

Note: we can't set CRYPTO_TFM_NEED_KEY for OPTIONAL_KEY algorithms, so
->setkey() for those must nevertheless be atomic.  That's fine for now
since only the crc32 and crc32c algorithms set OPTIONAL_KEY, and it's
not intended that OPTIONAL_KEY be used much.

[Cc stable mainly because when introducing the NEED_KEY flag I changed
 AF_ALG to rely on it; and unlike in-kernel crypto API users, AF_ALG
 previously didn't have this problem.  So these "incompletely keyed"
 states became theoretically accessible via AF_ALG -- though, the
 opportunities for causing real mischief seem pretty limited.]

Fixes: 9fa68f620041 ("crypto: hash - prevent using keyed hashes without setting key")
Cc: stable@vger.kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

1 files changed, 19 insertions, 9 deletions

diff --git a/crypto/ahash.c b/crypto/ahash.c
index 5d320a811f75..ca0d3e281fef 100644
--- a/crypto/ahash.c
+++ b/crypto/ahash.c
@@ -190,6 +190,21 @@ static int ahash_setkey_unaligned(struct crypto_ahash *tfm, const u8 *key,
 	return ret;
 }
 
+static int ahash_nosetkey(struct crypto_ahash *tfm, const u8 *key,
+			  unsigned int keylen)
+{
+	return -ENOSYS;
+}
+
+static void ahash_set_needkey(struct crypto_ahash *tfm)
+{
+	const struct hash_alg_common *alg = crypto_hash_alg_common(tfm);
+
+	if (tfm->setkey != ahash_nosetkey &&
+	    !(alg->base.cra_flags & CRYPTO_ALG_OPTIONAL_KEY))
+		crypto_ahash_set_flags(tfm, CRYPTO_TFM_NEED_KEY);
+}
+
 int crypto_ahash_setkey(struct crypto_ahash *tfm, const u8 *key,
 			unsigned int keylen)
 {
@@ -201,20 +216,16 @@ int crypto_ahash_setkey(struct crypto_ahash *tfm, const u8 *key,
 	else
 		err = tfm->setkey(tfm, key, keylen);
 
-	if (err)
+	if (unlikely(err)) {
+		ahash_set_needkey(tfm);
 		return err;
+	}
 
 	crypto_ahash_clear_flags(tfm, CRYPTO_TFM_NEED_KEY);
 	return 0;
 }
 EXPORT_SYMBOL_GPL(crypto_ahash_setkey);
 
-static int ahash_nosetkey(struct crypto_ahash *tfm, const u8 *key,
-			  unsigned int keylen)
-{
-	return -ENOSYS;
-}
-
 static inline unsigned int ahash_align_buffer_size(unsigned len,
 						   unsigned long mask)
 {
@@ -489,8 +500,7 @@ static int crypto_ahash_init_tfm(struct crypto_tfm *tfm)
 
 	if (alg->setkey) {
 		hash->setkey = alg->setkey;
-		if (!(alg->halg.base.cra_flags & CRYPTO_ALG_OPTIONAL_KEY))
-			crypto_ahash_set_flags(hash, CRYPTO_TFM_NEED_KEY);
+		ahash_set_needkey(hash);
 	}
 
 	return 0;