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, 13 insertions, 5 deletions

diff --git a/crypto/shash.c b/crypto/shash.c
index 44d297b82a8f..40311ccad3fa 100644
--- a/crypto/shash.c
+++ b/crypto/shash.c
@@ -53,6 +53,13 @@ static int shash_setkey_unaligned(struct crypto_shash *tfm, const u8 *key,
         return err;
 }
 
+static void shash_set_needkey(struct crypto_shash *tfm, struct shash_alg *alg)
+{
+        if (crypto_shash_alg_has_setkey(alg) &&
+            !(alg->base.cra_flags & CRYPTO_ALG_OPTIONAL_KEY))
+                crypto_shash_set_flags(tfm, CRYPTO_TFM_NEED_KEY);
+}
+
 int crypto_shash_setkey(struct crypto_shash *tfm, const u8 *key,
                         unsigned int keylen)
 {
@@ -65,8 +72,10 @@ int crypto_shash_setkey(struct crypto_shash *tfm, const u8 *key,
         else
                 err = shash->setkey(tfm, key, keylen);
 
-        if (err)
+        if (unlikely(err)) {
+                shash_set_needkey(tfm, shash);
                 return err;
+        }
 
         crypto_shash_clear_flags(tfm, CRYPTO_TFM_NEED_KEY);
         return 0;
@@ -373,7 +382,8 @@ int crypto_init_shash_ops_async(struct crypto_tfm *tfm)
         crt->final = shash_async_final;
         crt->finup = shash_async_finup;
         crt->digest = shash_async_digest;
-        crt->setkey = shash_async_setkey;
+        if (crypto_shash_alg_has_setkey(alg))
+                crt->setkey = shash_async_setkey;
 
         crypto_ahash_set_flags(crt, crypto_shash_get_flags(shash) &
                                     CRYPTO_TFM_NEED_KEY);
@@ -395,9 +405,7 @@ static int crypto_shash_init_tfm(struct crypto_tfm *tfm)
 
         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);
+        shash_set_needkey(hash, alg);
 
         return 0;
 }