Re: [PATCH net] selftests: net: cmsg_sender: retain the resolved address family

[Hangbin Liu <hangbin.liu@linux.dev>]

On Tue, Nov 10, 2026 at 03:39:18AM +0000, Jingjing Xu wrote:
> When neither -4 nor -6 is supplied, getaddrinfo() selects the socket
> family but opt.sock.family remains AF_UNSPEC. The cmsg and socket option
> helpers then take the IPv6 branch even for an IPv4 socket.
> 
> For example, an IPv4 loopback packet sent with -l 11 arrived with the
> default TTL of 64 on the test host. Using -L 11 instead failed with
> ENOPROTOOPT because the tool tried IPV6_UNICAST_HOPS on an IPv4 socket.
> Explicit -4 works in both cases.
> 
> Record the selected ai_family after successful address resolution so the
> helpers use the same family as the socket.
> 
> Discovered by Codex-assisted code inspection and tested with real
> loopback UDP traffic, without kernel instrumentation. Covered IPv4 and
> IPv6, automatic and explicit family selection, and cmsg and setsockopt
> hop limits. All eight cases receive the requested value after the fix.
> Built through the net selftest Makefile and with GCC -Wall -Werror.
> 
> Fixes: 2e5584e0f913 ("selftests/net: expand cmsg_ipv6.sh with ipv4")
> Signed-off-by: Jingjing Xu <xujingjing@cmss.chinamobile.com>
> ---
>  tools/testing/selftests/net/cmsg_sender.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/tools/testing/selftests/net/cmsg_sender.c b/tools/testing/selftests/net/cmsg_sender.c
> index 67a72b1a2f3d..01617a021338 100644
> --- a/tools/testing/selftests/net/cmsg_sender.c
> +++ b/tools/testing/selftests/net/cmsg_sender.c
> @@ -495,6 +495,7 @@ int main(int argc, char *argv[])
>  		goto err_free_buff;
>  	}
>  
> +	opt.sock.family = ai->ai_family;
>  	if (ai->ai_family == AF_INET6 && opt.sock.proto == IPPROTO_ICMP)
>  		opt.sock.proto = IPPROTO_ICMPV6;
>  
> base-commit: 1d5e2c57e9ffc134e14b3f837c8d7c53b508bd22
> -- 
> 2.53.0

Reviewed-by: Hangbin Liu <liuhangbin@kylinos.cn>