From: Luis Dallos <luis.dallos@googlemail.com>
Date: Tue, 2 Aug 2022 03:00:25 +0000 (-0400)
Subject: Fix startup failure on Windows 8.1 due to unsupported IPV6_USER_MTU socket option... 
X-Git-Tag: release-1.17.0rc1~42^2
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=refs%2Fpull%2F730%2Fhead;p=thirdparty%2Funbound.git

Fix startup failure on Windows 8.1 due to unsupported IPV6_USER_MTU socket option being set

Newer mingw-w64 (starting from 8.0.1) introduces support for `IPV6_USER_MTU` socket
option [1], which is not supported on Windows 8.1 and older [2]. As there is no way
to avoid this socket option from being picked at compile time when targeting older
versions of Windows, check for `setsockopt(..., IPV6_USER_MTU, ...)` failures at
runtime in order to avoid startup failure on those versions of Windows where the
`IPV6_USER_MTU` socket option is unsupported.

[1]: mirror/mingw-w64@e30bff4
[2]: `WSAGetLastError()` returns `WSAENOPROTOOPT` (`Bad protocol option`) error code
---

diff --git a/services/listen_dnsport.c b/services/listen_dnsport.c
index 1c7c177a0..467419b09 100644
--- a/services/listen_dnsport.c
+++ b/services/listen_dnsport.c
@@ -511,12 +511,14 @@ create_udp_sock(int family, int socktype, struct sockaddr* addr,
 		 * instead which is writable; IPV6_MTU is readonly there. */
 		if (setsockopt(s, IPPROTO_IPV6, IPV6_USER_MTU,
 			(void*)&mtu, (socklen_t)sizeof(mtu)) < 0) {
-			log_err("setsockopt(..., IPV6_USER_MTU, ...) failed: %s",
-				wsa_strerror(WSAGetLastError()));
-			sock_close(s);
-			*noproto = 0;
-			*inuse = 0;
-			return -1;
+			if (WSAGetLastError() != WSAENOPROTOOPT) {
+				log_err("setsockopt(..., IPV6_USER_MTU, ...) failed: %s",
+					wsa_strerror(WSAGetLastError()));
+				sock_close(s);
+				*noproto = 0;
+				*inuse = 0;
+				return -1;
+			}
 		}
 #   endif /* USE_WINSOCK */
 # endif /* IPv6 MTU */