ipv6: Set errno after ip_fib_metrics_init() in ip6_route_info_create().

JIRA: https://issues.redhat.com/browse/RHEL-84540

commit 9a81fc3
Author: Kuniyuki Iwashima <kuniyu@amazon.com>
Date:   Tue Mar 11 18:38:48 2025 -0700

    ipv6: Set errno after ip_fib_metrics_init() in ip6_route_info_create().

    While creating a new IPv6, we could get a weird -ENOMEM when
    RTA_NH_ID is set and either of the conditions below is true:

      1) CONFIG_IPV6_SUBTREES is enabled and rtm_src_len is specified
      2) nexthop_get() fails

    e.g.)

      # strace ip -6 route add fe80::dead:beef:dead:beef nhid 1 from ::
      recvmsg(3, {msg_iov=[{iov_base=[...[
        {error=-ENOMEM, msg=[... [...]]},
        [{nla_len=49, nla_type=NLMSGERR_ATTR_MSG}, "Nexthops can not be used with so"...]
      ]], iov_len=32768}], msg_iovlen=1, msg_controllen=0, msg_flags=0}, 0) = 148

    Let's set err explicitly after ip_fib_metrics_init() in
    ip6_route_info_create().

    Fixes: f88d8ea ("ipv6: Plumb support for nexthop object in a fib6_info")
    Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
    Reviewed-by: David Ahern <dsahern@kernel.org>
    Link: https://patch.msgid.link/20250312013854.61125-1-kuniyu@amazon.com
    Signed-off-by: Paolo Abeni <pabeni@redhat.com>

Signed-off-by: CKI Backport Bot <cki-ci-bot+cki-gitlab-backport-bot@redhat.com>

Author: CKI Backport Bot

net/ipv6/route.c

@@ -3798,10 +3798,12 @@ static struct fib6_info *ip6_route_info_create(struct fib6_config *cfg,
 	if (nh) {
 		if (rt->fib6_src.plen) {
 			NL_SET_ERR_MSG(extack, "Nexthops can not be used with source routing");
+			err = -EINVAL;
 			goto out_free;
 		}
 		if (!nexthop_get(nh)) {
 			NL_SET_ERR_MSG(extack, "Nexthop has been deleted");
+			err = -ENOENT;
 			goto out_free;
 		}
 		rt->nh = nh;