From 9be7b0f08340a063d961547b5d2663405f3fc162 Mon Sep 17 00:00:00 2001
From: Tim Ruffing <crypto@timruffing.de>
Date: Wed, 16 Jun 2021 10:33:41 +0200
Subject: [PATCH] Avoid computing out-of-bounds pointer.

This is a pedantic case of UB.
---
 src/ecdsa_impl.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/ecdsa_impl.h b/src/ecdsa_impl.h
index c32141e..8a99a17 100644
--- a/src/ecdsa_impl.h
+++ b/src/ecdsa_impl.h
@@ -112,7 +112,7 @@ static int secp256k1_der_parse_integer(secp256k1_scalar *r, const unsigned char
     if (secp256k1_der_read_len(&rlen, sig, sigend) == 0) {
         return 0;
     }
-    if (rlen == 0 || *sig + rlen > sigend) {
+    if (rlen == 0 || rlen > (size_t)(sigend - *sig)) {
         /* Exceeds bounds or not at least length 1 (X.690-0207 8.3.1).  */
         return 0;
     }