wrap_nettle_hash_fast: avoid calling _update with zero-length input

As Nettle's hash update functions internally call memcpy, providing
zero-length input may cause undefined behavior.

Signed-off-by: Daiki Ueno <ueno@gnu.org>

1 files changed, 3 insertions, 1 deletions

diff --git a/lib/nettle/mac.c b/lib/nettle/mac.c
index f9d4d7a8df..35e070fab0 100644
--- a/lib/nettle/mac.c
+++ b/lib/nettle/mac.c
@@ -788,7 +788,9 @@ static int wrap_nettle_hash_fast(gnutls_digest_algorithm_t algo,
 	if (ret < 0)
 		return gnutls_assert_val(ret);
 
-	ctx.update(&ctx, text_size, text);
+	if (text_size > 0) {
+		ctx.update(&ctx, text_size, text);
+	}
 	ctx.digest(&ctx, ctx.length, digest);
 
 	return 0;