[PATCH 4.17 41/46] netfilter: ip6t_rpfilter: provide input interface for route lookup

From: Greg Kroah-Hartman
Date: Fri Jul 06 2018 - 02:09:57 EST

4.17-stable review patch. If anyone has any objections, please let me know.


From: Vincent Bernat <vincent@xxxxxxxxx>

commit cede24d1b21d68d84ac5a36c44f7d37daadcc258 upstream.

In commit 47b7e7f82802, this bit was removed at the same time the
RT6_LOOKUP_F_IFACE flag was removed. However, it is needed when
link-local addresses are used, which is a very common case: when
packets are routed, neighbor solicitations are done using link-local
addresses. For example, the following neighbor solicitation is not
matched by "-m rpfilter":

IP6 fe80::5254:33ff:fe00:1 > ff02::1:ff00:3: ICMP6, neighbor
solicitation, who has 2001:db8::5254:33ff:fe00:3, length 32

Commit 47b7e7f82802 doesn't quite explain why we shouldn't use
RT6_LOOKUP_F_IFACE in the rpfilter case. I suppose the interface check
later in the function would make it redundant. However, the remaining
of the routing code is using RT6_LOOKUP_F_IFACE when there is no
source address (which matches rpfilter's case with a non-unicast
destination, like with neighbor solicitation).

Signed-off-by: Vincent Bernat <vincent@xxxxxxxxx>
Fixes: 47b7e7f82802 ("netfilter: don't set F_IFACE on ipv6 fib lookups")
Signed-off-by: Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

net/ipv6/netfilter/ip6t_rpfilter.c | 2 ++
1 file changed, 2 insertions(+)

--- a/net/ipv6/netfilter/ip6t_rpfilter.c
+++ b/net/ipv6/netfilter/ip6t_rpfilter.c
@@ -48,6 +48,8 @@ static bool rpfilter_lookup_reverse6(str

fl6.flowi6_mark = flags & XT_RPFILTER_VALID_MARK ? skb->mark : 0;
+ if ((flags & XT_RPFILTER_LOOSE) == 0)
+ fl6.flowi6_oif = dev->ifindex;

rt = (void *)ip6_route_lookup(net, &fl6, skb, lookup_flags);
if (rt->dst.error)