[PATCH net] selftests/fib_tests: ping from dummy0 in fib_rp_filter_test()

[Peilin Ye <yepeilin.cs@gmail.com>]

From: Peilin Ye <peilin.ye@bytedance.com>

Currently rp_filter tests in fib_tests.sh:fib_rp_filter_test() are
failing.  ping sockets are bound to dummy1 using the "-I" option
(SO_BINDTODEVICE), but socket lookup is failing when receiving ping
replies, since the routing table thinks they belong to dummy0.

For example, suppose ping is using a SOCK_RAW socket for ICMP messages.
When receiving ping replies, in __raw_v4_lookup(), sk->sk_bound_dev_if
is 3 (dummy1), but dif (skb_rtable(skb)->rt_iif) says 2 (dummy0), so the
raw_sk_bound_dev_eq() check fails.  Similar things happen in
ping_lookup() for SOCK_ICMP sockets.

Fix the tests by binding to dummy0 instead.  Redirect ping requests to
dummy1 before redirecting them again to lo, so that sk->sk_bound_dev_if
agrees with our routing table.

These tests used to pass due to a bug [1] in iputils, where "ping -I"
actually did not bind ICMP message sockets to device.  The bug has been
fixed by iputils commit f455fee41c07 ("ping: also bind the ICMP socket
to the specific device") in 2016, which is why our rp_filter tests
started to fail.  See [2] .

Tested with ping from iputils 20210722-41-gf9fb573:

$ ./fib_tests.sh -t rp_filter

IPv4 rp_filter tests
    TEST: rp_filter passes local packets		[ OK ]
    TEST: rp_filter passes loopback packets		[ OK ]

[1] https://github.com/iputils/iputils/issues/55
[2] https://github.com/iputils/iputils/commit/f455fee41c077d4b700a473b2f5b3487b8febc1d

Reported-by: Hangbin Liu <liuhangbin@gmail.com>
Fixes: adb701d6cfa4 ("selftests: add a test case for rp_filter")
Reviewed-by: Cong Wang <cong.wang@bytedance.com>
Signed-off-by: Peilin Ye <peilin.ye@bytedance.com>
---
 tools/testing/selftests/net/fib_tests.sh | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/net/fib_tests.sh b/tools/testing/selftests/net/fib_tests.sh
index 5abe92d55b69..b8bceae00f8e 100755
--- a/tools/testing/selftests/net/fib_tests.sh
+++ b/tools/testing/selftests/net/fib_tests.sh
@@ -453,15 +453,19 @@ fib_rp_filter_test()
 	$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 dummy0 parent root handle 1: fq_codel
+	$NS_EXEC tc filter add dev dummy0 parent 1: protocol arp basic action mirred egress redirect dev dummy1
+	$NS_EXEC tc filter add dev dummy0 parent 1: protocol ip basic action mirred egress redirect dev dummy1
+
 	$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"
+	run_cmd "ip netns exec ns1 ping -I dummy0 -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"
+	run_cmd "ip netns exec ns1 ping -I dummy0 -w1 -c1 127.0.0.1"
 	log_test $? 0 "rp_filter passes loopback packets"
 
 	cleanup
-- 
2.20.1