[PATCH] net: setsockopt: fix IPV6_UNICAST_IF option for connected sockets

[Richard Gobert <richardbgobert@gmail.com>]

Change the behaviour of ip6_datagram_connect to consider the interface
set by the IPV6_UNICAST_IF socket option, similarly to udpv6_sendmsg.

This change is the IPv6 counterpart of the fix for IP_UNICAST_IF.
The tests introduced by that patch showed that the incorrect
behavior is present in IPv6 as well.
This patch fixes the broken test.

Reported-by: kernel test robot <oliver.sang@intel.com>
Link: https://lore.kernel.org/r/202210062117.c7eef1a3-oliver.sang@intel.com

Signed-off-by: Richard Gobert <richardbgobert@gmail.com>
---
 net/ipv6/datagram.c | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/net/ipv6/datagram.c b/net/ipv6/datagram.c
index 7c7155b48f17..c3999f9e3545 100644
--- a/net/ipv6/datagram.c
+++ b/net/ipv6/datagram.c
@@ -42,24 +42,30 @@ static void ip6_datagram_flow_key_init(struct flowi6 *fl6, struct sock *sk)
 {
 	struct inet_sock *inet = inet_sk(sk);
 	struct ipv6_pinfo *np = inet6_sk(sk);
+	int oif;
 
 	memset(fl6, 0, sizeof(*fl6));
 	fl6->flowi6_proto = sk->sk_protocol;
 	fl6->daddr = sk->sk_v6_daddr;
 	fl6->saddr = np->saddr;
-	fl6->flowi6_oif = sk->sk_bound_dev_if;
+	oif = sk->sk_bound_dev_if;
 	fl6->flowi6_mark = sk->sk_mark;
 	fl6->fl6_dport = inet->inet_dport;
 	fl6->fl6_sport = inet->inet_sport;
 	fl6->flowlabel = np->flow_label;
 	fl6->flowi6_uid = sk->sk_uid;
 
-	if (!fl6->flowi6_oif)
-		fl6->flowi6_oif = np->sticky_pktinfo.ipi6_ifindex;
+	if (!oif)
+		oif = np->sticky_pktinfo.ipi6_ifindex;
 
-	if (!fl6->flowi6_oif && ipv6_addr_is_multicast(&fl6->daddr))
-		fl6->flowi6_oif = np->mcast_oif;
+	if (!oif) {
+		if (ipv6_addr_is_multicast(&fl6->daddr))
+			oif = np->mcast_oif;
+		else
+			oif = np->ucast_oif;
+	}
 
+	fl6->flowi6_oif = oif;
 	security_sk_classify_flow(sk, flowi6_to_flowi_common(fl6));
 }
 
-- 
2.36.1