crypto: des_generic - Forbid 2-key in 3DES and add helpers

This patch adds a requirement to the generic 3DES implementation
such that 2-key 3DES (K1 == K3) is no longer allowed in FIPS mode.

We will also provide helpers that may be used by drivers that
implement 3DES to make the same check.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

crypto/des_generic.c

@@ -862,14 +862,11 @@ static void des_decrypt(struct crypto_tfm *tfm, u8 *dst, const u8 *src)
 int __des3_ede_setkey(u32 *expkey, u32 *flags, const u8 *key,
 		      unsigned int keylen)
 {
-	const u32 *K = (const u32 *)key;
+	int err;
 
-	if (unlikely(!((K[0] ^ K[2]) | (K[1] ^ K[3])) ||
-		     !((K[2] ^ K[4]) | (K[3] ^ K[5]))) &&
-		     (*flags & CRYPTO_TFM_REQ_FORBID_WEAK_KEYS)) {
-		*flags |= CRYPTO_TFM_RES_WEAK_KEY;
-		return -EINVAL;
-	}
+	err = __des3_verify_key(flags, key);
+	if (unlikely(err))
+		return err;
 
 	des_ekey(expkey, key); expkey += DES_EXPKEY_WORDS; key += DES_KEY_SIZE;
 	dkey(expkey, key); expkey += DES_EXPKEY_WORDS; key += DES_KEY_SIZE;