crypto: arm64/aes-ccm - fix bugs in non-NEON fallback routine

Commit 5092fcf3 ("crypto: arm64/aes-ce-ccm: add non-SIMD generic
fallback") introduced C fallback code to replace the NEON routines
when invoked from a context where the NEON is not available (i.e.,
from the context of a softirq taken while the NEON is already being
used in kernel process context)

Fix two logical flaws in the MAC calculation of the associated data.
Reported-by: NEric Biggers <ebiggers@kernel.org>
Fixes: 5092fcf3 ("crypto: arm64/aes-ce-ccm: add non-SIMD generic fallback")
Cc: stable@vger.kernel.org
Signed-off-by: NArd Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: NHerbert Xu <herbert@gondor.apana.org.au>

arch/arm64/crypto/aes-ce-ccm-glue.c

@@ -125,7 +125,7 @@ static void ccm_update_mac(struct crypto_aes_ctx *key, u8 mac[], u8 const in[],
 			abytes -= added;
 		}
 
-		while (abytes > AES_BLOCK_SIZE) {
+		while (abytes >= AES_BLOCK_SIZE) {
 			__aes_arm64_encrypt(key->key_enc, mac, mac,
 					    num_rounds(key));
 			crypto_xor(mac, in, AES_BLOCK_SIZE);
@@ -139,8 +139,6 @@ static void ccm_update_mac(struct crypto_aes_ctx *key, u8 mac[], u8 const in[],
 					    num_rounds(key));
 			crypto_xor(mac, in, abytes);
 			*macp = abytes;
-		} else {
-			*macp = 0;
 		}
 	}
 }