netfilter: ip6t_rpfilter: Fix regression with VRF interfaces

When calling ip6_route_lookup() for the packet arriving on the VRF
interface, the result is always the real (slave) interface. Expect this
when validating the result.

Fixes: acc641a ("netfilter: rpfilter/fib: Populate flowic_l3mdev field")
Signed-off-by: Phil Sutter <phil@nwl.cc>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

Author: Phil Sutter

net/ipv6/netfilter/ip6t_rpfilter.c

@@ -72,7 +72,9 @@ static bool rpfilter_lookup_reverse6(struct net *net, const struct sk_buff *skb,
 		goto out;
 	}
 
-	if (rt->rt6i_idev->dev == dev || (flags & XT_RPFILTER_LOOSE))
+	if (rt->rt6i_idev->dev == dev ||
+	    l3mdev_master_ifindex_rcu(rt->rt6i_idev->dev) == dev->ifindex ||
+	    (flags & XT_RPFILTER_LOOSE))
 		ret = true;
  out:
 	ip6_rt_put(rt);

tools/testing/selftests/netfilter/rpath.sh

@@ -62,10 +62,16 @@ ip -net "$ns1" a a fec0:42::2/64 dev v0 nodad
 ip -net "$ns2" a a fec0:42::1/64 dev d0 nodad
 
 # firewall matches to test
-[ -n "$iptables" ] && ip netns exec "$ns2" \
-	"$iptables" -t raw -A PREROUTING -s 192.168.0.0/16 -m rpfilter
-[ -n "$ip6tables" ] && ip netns exec "$ns2" \
-	"$ip6tables" -t raw -A PREROUTING -s fec0::/16 -m rpfilter
+[ -n "$iptables" ] && {
+	common='-t raw -A PREROUTING -s 192.168.0.0/16'
+	ip netns exec "$ns2" "$iptables" $common -m rpfilter
+	ip netns exec "$ns2" "$iptables" $common -m rpfilter --invert
+}
+[ -n "$ip6tables" ] && {
+	common='-t raw -A PREROUTING -s fec0::/16'
+	ip netns exec "$ns2" "$ip6tables" $common -m rpfilter
+	ip netns exec "$ns2" "$ip6tables" $common -m rpfilter --invert
+}
 [ -n "$nft" ] && ip netns exec "$ns2" $nft -f - <<EOF
 table inet t {
 	chain c {
@@ -89,6 +95,11 @@ ipt_zero_rule() { # (command)
 	[ -n "$1" ] || return 0
 	ip netns exec "$ns2" "$1" -t raw -vS | grep -q -- "-m rpfilter -c 0 0"
 }
+ipt_zero_reverse_rule() { # (command)
+	[ -n "$1" ] || return 0
+	ip netns exec "$ns2" "$1" -t raw -vS | \
+		grep -q -- "-m rpfilter --invert -c 0 0"
+}
 nft_zero_rule() { # (family)
 	[ -n "$nft" ] || return 0
 	ip netns exec "$ns2" "$nft" list chain inet t c | \
@@ -101,8 +112,7 @@ netns_ping() { # (netns, args...)
 	ip netns exec "$netns" ping -q -c 1 -W 1 "$@" >/dev/null
 }
 
-testrun() {
-	# clear counters first
+clear_counters() {
 	[ -n "$iptables" ] && ip netns exec "$ns2" "$iptables" -t raw -Z
 	[ -n "$ip6tables" ] && ip netns exec "$ns2" "$ip6tables" -t raw -Z
 	if [ -n "$nft" ]; then
@@ -111,6 +121,10 @@ testrun() {
 			ip netns exec "$ns2" $nft -s list table inet t;
 		) | ip netns exec "$ns2" $nft -f -
 	fi
+}
+
+testrun() {
+	clear_counters
 
 	# test 1: martian traffic should fail rpfilter matches
 	netns_ping "$ns1" -I v0 192.168.42.1 && \
@@ -120,9 +134,13 @@ testrun() {
 
 	ipt_zero_rule "$iptables" || die "iptables matched martian"
 	ipt_zero_rule "$ip6tables" || die "ip6tables matched martian"
+	ipt_zero_reverse_rule "$iptables" && die "iptables not matched martian"
+	ipt_zero_reverse_rule "$ip6tables" && die "ip6tables not matched martian"
 	nft_zero_rule ip || die "nft IPv4 matched martian"
 	nft_zero_rule ip6 || die "nft IPv6 matched martian"
 
+	clear_counters
+
 	# test 2: rpfilter match should pass for regular traffic
 	netns_ping "$ns1" 192.168.23.1 || \
 		die "regular ping 192.168.23.1 failed"
@@ -131,6 +149,8 @@ testrun() {
 
 	ipt_zero_rule "$iptables" && die "iptables match not effective"
 	ipt_zero_rule "$ip6tables" && die "ip6tables match not effective"
+	ipt_zero_reverse_rule "$iptables" || die "iptables match over-effective"
+	ipt_zero_reverse_rule "$ip6tables" || die "ip6tables match over-effective"
 	nft_zero_rule ip && die "nft IPv4 match not effective"
 	nft_zero_rule ip6 && die "nft IPv6 match not effective"