selftests: nft_nat: Improve port shadow test stability

Setup phase in test_port_shadow() relied upon a race-condition:
Listening nc on port 1405 was started in background before attempting to
create the fake conntrack entry using the same source port. If listening
nc won, fake conntrack entry could not be created causing wrong
behaviour. Reorder nc calls to fix this and introduce a short delay
before testing the setup to wait for listening nc process startup.

Fixes: 465f15a6d1a8f ("selftests: nft_nat: add udp hole punch test case")
Signed-off-by: Phil Sutter <phil@nwl.cc>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

diff --git a/tools/testing/selftests/netfilter/nft_nat.sh b/tools/testing/selftests/netfilter/nft_nat.sh
index da1c1e4..905c033 100755 (executable)
--- a/tools/testing/selftests/netfilter/nft_nat.sh
+++ b/tools/testing/selftests/netfilter/nft_nat.sh
@@ -759,14 +759,16 @@ test_port_shadow()
        local result=""
        local logmsg=""
 
+       # make shadow entry, from client (ns2), going to (ns1), port 41404, sport 1405.
+       echo "fake-entry" | ip netns exec "$ns2" nc -w 1 -p 1405 -u "$daddrc" 41404 > /dev/null
+
        echo ROUTER | ip netns exec "$ns0" nc -w 5 -u -l -p 1405 >/dev/null 2>&1 &
        nc_r=$!
 
        echo CLIENT | ip netns exec "$ns2" nc -w 5 -u -l -p 1405 >/dev/null 2>&1 &
        nc_c=$!
 
-       # make shadow entry, from client (ns2), going to (ns1), port 41404, sport 1405.
-       echo "fake-entry" | ip netns exec "$ns2" nc -w 1 -p 1405 -u "$daddrc" 41404 > /dev/null
+       sleep 0.3
 
        # ns1 tries to connect to ns0:1405.  With default settings this should connect
        # to client, it matches the conntrack entry created above.