lib:crypto: Use constant time memory comparison to check HMAC

Signed-off-by: Joseph Sutton <josephsutton@catalyst.net.nz>
Reviewed-by: Andreas Schneider <asn@samba.org>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>

diff --git a/lib/crypto/gnutls_aead_aes_256_cbc_hmac_sha512.c b/lib/crypto/gnutls_aead_aes_256_cbc_hmac_sha512.c
index fc4d21f4ec56536f1ec33cdb7ead92d1f2e7f354..e0877a03f5299c672748bb520c96a027fe28515e 100644 (file)
--- a/lib/crypto/gnutls_aead_aes_256_cbc_hmac_sha512.c
+++ b/lib/crypto/gnutls_aead_aes_256_cbc_hmac_sha512.c
@@ -282,7 +282,7 @@ samba_gnutls_aead_aes_256_cbc_hmac_sha512_decrypt(TALLOC_CTX *mem_ctx,
        uint8_t padding;
        size_t i;
        NTSTATUS status;
-       int cmp;
+       bool equal;
        int rc;
 
        if (cdk->length == 0 || ciphertext->length == 0 ||
@@ -333,8 +333,8 @@ samba_gnutls_aead_aes_256_cbc_hmac_sha512_decrypt(TALLOC_CTX *mem_ctx,
        }
        gnutls_hmac_deinit(hmac_hnd, auth_data);
 
-       cmp = memcmp(auth_data, auth_tag, sizeof(auth_data));
-       if (cmp != 0) {
+       equal = mem_equal_const_time(auth_data, auth_tag, sizeof(auth_data));
+       if (!equal) {
                return NT_STATUS_DECRYPTION_FAILED;
        }