Merge branch 'ipv4-relax-source-validation-check-for-loopback-packets'

Cong Wang says:

====================
ipv4: relax source validation check for loopback packets

This patchset fixes a corner case when loopback packets get dropped
by rp_filter when we route them from veth to lo. Patch 1 is the fix
and patch 2 provides a simplified test case for this scenario.
====================
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/fib_frontend.c

@@ -388,6 +388,11 @@ static int __fib_validate_source(struct sk_buff *skb, __be32 src, __be32 dst,
 	fib_combine_itag(itag, &res);
 
 	dev_match = fib_info_nh_uses_dev(res.fi, dev);
+	/* This is not common, loopback packets retain skb_dst so normally they
+	 * would not even hit this slow path.
+	 */
+	dev_match = dev_match || (res.type == RTN_LOCAL &&
+				  dev == net->loopback_dev);
 	if (dev_match) {
 		ret = FIB_RES_NHC(res)->nhc_scope >= RT_SCOPE_HOST;
 		return ret;

tools/testing/selftests/net/fib_tests.sh

@@ -9,12 +9,13 @@ ret=0
 ksft_skip=4
 
 # all tests in this script. Can be overridden with -t option
-TESTS="unregister down carrier nexthop ipv6_rt ipv4_rt ipv6_addr_metric ipv4_addr_metric ipv6_route_metrics ipv4_route_metrics ipv4_route_v6_gw"
+TESTS="unregister down carrier nexthop ipv6_rt ipv4_rt ipv6_addr_metric ipv4_addr_metric ipv6_route_metrics ipv4_route_metrics ipv4_route_v6_gw rp_filter"
 
 VERBOSE=0
 PAUSE_ON_FAIL=no
 PAUSE=no
 IP="ip -netns ns1"
+NS_EXEC="ip netns exec ns1"
 
 log_test()
 {
@@ -433,6 +434,37 @@ fib_carrier_test()
 	fib_carrier_unicast_test
 }
 
+fib_rp_filter_test()
+{
+	echo
+	echo "IPv4 rp_filter tests"
+
+	setup
+
+	set -e
+	$IP link set dev lo address 52:54:00:6a:c7:5e
+	$IP link set dummy0 address 52:54:00:6a:c7:5e
+	$IP link add dummy1 type dummy
+	$IP link set dummy1 address 52:54:00:6a:c7:5e
+	$IP link set dev dummy1 up
+	$NS_EXEC sysctl -qw net.ipv4.conf.all.rp_filter=1
+	$NS_EXEC sysctl -qw net.ipv4.conf.all.accept_local=1
+	$NS_EXEC sysctl -qw net.ipv4.conf.all.route_localnet=1
+
+	$NS_EXEC tc qd add dev dummy1 parent root handle 1: fq_codel
+	$NS_EXEC tc filter add dev dummy1 parent 1: protocol arp basic action mirred egress redirect dev lo
+	$NS_EXEC tc filter add dev dummy1 parent 1: protocol ip basic action mirred egress redirect dev lo
+	set +e
+
+	run_cmd "ip netns exec ns1 ping -I dummy1 -w1 -c1 198.51.100.1"
+	log_test $? 0 "rp_filter passes local packets"
+
+	run_cmd "ip netns exec ns1 ping -I dummy1 -w1 -c1 127.0.0.1"
+	log_test $? 0 "rp_filter passes loopback packets"
+
+	cleanup
+}
+
 ################################################################################
 # Tests on nexthop spec
 
@@ -1557,6 +1589,7 @@ do
 	fib_unreg_test|unregister)	fib_unreg_test;;
 	fib_down_test|down)		fib_down_test;;
 	fib_carrier_test|carrier)	fib_carrier_test;;
+	fib_rp_filter_test|rp_filter)	fib_rp_filter_test;;
 	fib_nexthop_test|nexthop)	fib_nexthop_test;;
 	ipv6_route_test|ipv6_rt)	ipv6_route_test;;
 	ipv4_route_test|ipv4_rt)	ipv4_route_test;;