crypto: remove CRYPTO_TFM_RES_BAD_KEY_LEN

The CRYPTO_TFM_RES_BAD_KEY_LEN flag was apparently meant as a way to
make the ->setkey() functions provide more information about errors.

However, no one actually checks for this flag, which makes it pointless.

Also, many algorithms fail to set this flag when given a bad length key.
Reviewing just the generic implementations, this is the case for
aes-fixed-time, cbcmac, echainiv, nhpoly1305, pcrypt, rfc3686, rfc4309,
rfc7539, rfc7539esp, salsa20, seqiv, and xcbc.  But there are probably
many more in arch/*/crypto/ and drivers/crypto/.

Some algorithms can even set this flag when the key is the correct
length.  For example, authenc and authencesn set it when the key payload
is malformed in any way (not just a bad length), the atmel-sha and ccree
drivers can set it if a memory allocation fails, and the chelsio driver
sets it for bad auth tag lengths, not just bad key lengths.

So even if someone actually wanted to start checking this flag (which
seems unlikely, since it's been unused for a long time), there would be
a lot of work needed to get it working correctly.  But it would probably
be much better to go back to the drawing board and just define different
return values, like -EINVAL if the key is invalid for the algorithm vs.
-EKEYREJECTED if the key was rejected by a policy like "no weak keys".
That would be much simpler, less error-prone, and easier to test.

So just remove this flag.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Reviewed-by: Horia Geantă <horia.geanta@nxp.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

1 files changed, 2 insertions, 6 deletions

diff --git a/include/crypto/xts.h b/include/crypto/xts.h
index 15ae7fdc0478..57b2c52928db 100644
--- a/include/crypto/xts.h
+++ b/include/crypto/xts.h
@@ -17,10 +17,8 @@ static inline int xts_check_key(struct crypto_tfm *tfm,
 	 * key consists of keys of equal size concatenated, therefore
 	 * the length must be even.
 	 */
-	if (keylen % 2) {
-		*flags |= CRYPTO_TFM_RES_BAD_KEY_LEN;
+	if (keylen % 2)
 		return -EINVAL;
-	}
 
 	/* ensure that the AES and tweak key are not identical */
 	if (fips_enabled &&
@@ -39,10 +37,8 @@ static inline int xts_verify_key(struct crypto_skcipher *tfm,
 	 * key consists of keys of equal size concatenated, therefore
 	 * the length must be even.
 	 */
-	if (keylen % 2) {
-		crypto_skcipher_set_flags(tfm, CRYPTO_TFM_RES_BAD_KEY_LEN);
+	if (keylen % 2)
 		return -EINVAL;
-	}
 
 	/* ensure that the AES and tweak key are not identical */
 	if ((fips_enabled || (crypto_skcipher_get_flags(tfm) &