tests/shell: Test for fixed extension registration

Use strace to look at iptables-restore behaviour with typically
problematic input (conntrack revision 0 is no longer supported by
current kernels) to make sure the fix in commit a1eaaceb0460b
("libxtables: Simplify pending extension registration") is still
effective.

Signed-off-by: Phil Sutter <phil@nwl.cc>

diff --git a/iptables/tests/shell/testcases/ipt-restore/0017-pointless-compat-checks_0 b/iptables/tests/shell/testcases/ipt-restore/0017-pointless-compat-checks_0
new file mode 100755 (executable)
index 0000000..cf73de3
--- /dev/null
+++ b/iptables/tests/shell/testcases/ipt-restore/0017-pointless-compat-checks_0
@@ -0,0 +1,25 @@
+#!/bin/bash
+
+# A bug in extension registration would leave unsupported older extension
+# revisions in pending list and get compatibility checked again for each rule
+# using them. With SELinux enabled, the resulting socket() call per rule leads
+# to significant slowdown (~50% performance in worst cases).
+
+set -e
+
+strace --version >/dev/null || { echo "skip for missing strace"; exit 0; }
+
+RULESET="$(
+       echo "*filter"
+       for ((i = 0; i < 100; i++)); do
+               echo "-A FORWARD -m conntrack --ctstate NEW"
+       done
+       echo "COMMIT"
+)"
+
+cmd="$XT_MULTI iptables-restore"
+socketcount=$(strace -esocket $cmd <<< "$RULESET" 2>&1 | wc -l)
+
+# unpatched iptables-restore would open 111 sockets,
+# patched only 12 but keep a certain margin for future changes
+[[ $socketcount -lt 20 ]]