xfrm: Only add l3mdev oif to dst lookups

Subash reported that commit 42a7b32b73d6 ("xfrm: Add oif to dst lookups")
broke a wifi use case that uses fib rules and xfrms. The intent of
42a7b32b73d6 was driven by VRFs with IPsec. As a compromise relax the
use of oif in xfrm lookups to L3 master devices only (ie., oif is either
an L3 master device or is enslaved to a master device).

Fixes: 42a7b32b73d6 ("xfrm: Add oif to dst lookups")
Reported-by: Subash Abhinov Kasiviswanathan <subashab@codeaurora.org>
Signed-off-by: David Ahern <dsa@cumulusnetworks.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>

net/ipv4/xfrm4_policy.c

@@ -29,7 +29,7 @@ static struct dst_entry *__xfrm4_dst_lookup(struct net *net, struct flowi4 *fl4,
 	memset(fl4, 0, sizeof(*fl4));
 	fl4->daddr = daddr->a4;
 	fl4->flowi4_tos = tos;
-	fl4->flowi4_oif = oif;
+	fl4->flowi4_oif = l3mdev_master_ifindex_by_index(net, oif);
 	if (saddr)
 		fl4->saddr = saddr->a4;
 

net/ipv6/xfrm6_policy.c

@@ -36,7 +36,7 @@ static struct dst_entry *xfrm6_dst_lookup(struct net *net, int tos, int oif,
 	int err;
 
 	memset(&fl6, 0, sizeof(fl6));
-	fl6.flowi6_oif = oif;
+	fl6.flowi6_oif = l3mdev_master_ifindex_by_index(net, oif);
 	fl6.flowi6_flags = FLOWI_FLAG_SKIP_NH_OIF;
 	memcpy(&fl6.daddr, daddr, sizeof(fl6.daddr));
 	if (saddr)