From: Joseph Sutton <josephsutton@catalyst.net.nz>
Date: Tue, 2 Aug 2022 02:34:55 +0000 (+1200)
Subject: lib:crypto: Use constant time memory comparison to check HMAC
X-Git-Tag: talloc-2.4.0~1092
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=121e439e24a9c03ae900ffca1ae1dda8e059008c;p=thirdparty%2Fsamba.git

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 fc4d21f4ec5..e0877a03f52 100644
--- 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;
 	}