tests/int: add a test for a seccomp-killed init

SCMP_ACT_KILL kills a single thread, so "runc init" is left as a zombie
thread group leader surrounded by live threads that keep its descriptors
open. Check that runc reports that instead of hanging.

The container gets its own stdio rather than the one bats captures: were
this to regress, the leftover threads would keep bats' end open, and the
suite would hang instead of reporting a failure.

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
Assisted-by: Claude Opus 5

tests/integration/run.bats

@@ -218,3 +218,31 @@ EOF
 	run -1 runc run test_hello
 	assert_output --partial "invalid rootfs: / is not allowed"
 }
+
+# https://github.com/opencontainers/runc/issues/5087
+@test "runc run [seccomp SCMP_ACT_KILL kills init]" {
+	# SCMP_ACT_KILL only kills the offending thread, leaving runc init with a
+	# zombie thread group leader and live threads holding its ends of the sync
+	# socket and the exec fifo open. Make sure runc notices that init is gone,
+	# rather than waiting for an EOF that can never arrive.
+	update_config '   .process.args = ["/bin/true"]
+			| .process.terminal = false
+			| .process.rlimits = [{"type": "RLIMIT_CORE", "soft": 0, "hard": 0}]
+			| .linux.seccomp = {
+				"defaultAction": "SCMP_ACT_ALLOW",
+				"syscalls": [{"names": ["write"], "action": "SCMP_ACT_KILL"}]
+			}'
+
+	# Give runc its own stdio. Should this regress, the leftover threads keep
+	# it open, and bats would hang on it instead of failing the test.
+	local log="$BATS_TEST_TMPDIR/run-5087.log" ret=0
+	timeout -k 5 30 runc run test_busybox </dev/null >"$log" 2>&1 || ret=$?
+	run -0 cat "$log"
+
+	# Not 124 or 137, which mean the timeout fired, i.e. runc has hung.
+	[ "$ret" -eq 1 ]
+	assert_output --partial "container init process died unexpectedly"
+	# The leftover threads have to be gone as well, or the container's cgroup
+	# can not be removed, and the next test to use this name would fail.
+	refute_output --partial "unable to destroy container"
+}