Merge bitcoin-core/secp256k1#952: Avoid computing out-of-bounds pointer.

real-or-random · real-or-random · commit 920a0e5fa642 · 2021-10-17T11:55:31.000+02:00
9be7b0f Avoid computing out-of-bounds pointer. (Tim Ruffing) Pull request description: This is a pedantic case of UB. Spotted in bitcoin#879. ACKs for top commit: elichai: ACK 9be7b0f practicalswift: cr ACK 9be7b0f sipa: ACK 9be7b0f Tree-SHA512: a9d028c4cdb37ad0d5fcf0d2f678eef732a653d37155a69a20272c6b283c28e083172485d7a37dc4a7c6100b22a6f5b6a92e729239031be228cc511842ee35e8
diff --git 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;
     }

Original file line number	Diff line number	Diff line change
`@@ -112,7 +112,7 @@ static int secp256k1_der_parse_integer(secp256k1_scalar *r, const unsigned char`
`112`	`112`	`if (secp256k1_der_read_len(&rlen, sig, sigend) == 0) {`
`113`	`113`	`return 0;`
`114`	`114`	`}`
`115`		`- if (rlen == 0 \|\| *sig + rlen > sigend) {`
	`115`	`+ if (rlen == 0 \|\| rlen > (size_t)(sigend - *sig)) {`
`116`	`116`	`/* Exceeds bounds or not at least length 1 (X.690-0207 8.3.1). */`
`117`	`117`	`return 0;`
`118`	`118`	`}`