seccomp: fix flag test to actually check the value

Add a debug print of seccomp flags value, so the test can check
those (without using something like strace, that is).

Amend the flags setting test with the numeric values expected, and the
logic to check those.

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
(cherry picked from commit 26dc55e)
Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

Author: kolyshkin

libcontainer/seccomp/patchbpf/enosys_linux.go

@@ -653,6 +653,9 @@ func filterFlags(config *configs.Seccomp, filter *libseccomp.ScmpFilter) (flags
 }
 
 func sysSeccompSetFilter(flags uint, filter []unix.SockFilter) (fd int, err error) {
+	// This debug output is validated in tests/integration/seccomp.bats
+	// by the SECCOMP_FILTER_FLAG_* test.
+	logrus.Debugf("seccomp filter flags: %d", flags)
 	fprog := unix.SockFprog{
 		Len:    uint16(len(filter)),
 		Filter: &filter[0],

tests/integration/seccomp.bats

@@ -70,31 +70,47 @@ function teardown() {
 	# Linux 4.14: SECCOMP_FILTER_FLAG_LOG
 	# Linux 4.17: SECCOMP_FILTER_FLAG_SPEC_ALLOW
 	requires_kernel 4.17
-	SECCOMP_FILTER_FLAGS=(
-		'' # no flag
-		'"SECCOMP_FILTER_FLAG_LOG"'
-		'"SECCOMP_FILTER_FLAG_SPEC_ALLOW"'
-		'"SECCOMP_FILTER_FLAG_TSYNC"'
-		'"SECCOMP_FILTER_FLAG_LOG","SECCOMP_FILTER_FLAG_SPEC_ALLOW"'
-		'"SECCOMP_FILTER_FLAG_LOG","SECCOMP_FILTER_FLAG_TSYNC"'
-		'"SECCOMP_FILTER_FLAG_SPEC_ALLOW","SECCOMP_FILTER_FLAG_TSYNC"'
-		'"SECCOMP_FILTER_FLAG_LOG","SECCOMP_FILTER_FLAG_SPEC_ALLOW","SECCOMP_FILTER_FLAG_TSYNC"'
+
+	update_config '   .process.args = ["/bin/sh", "-c", "mkdir /dev/shm/foo"]
+			| .process.noNewPrivileges = false
+			| .linux.seccomp = {
+				"defaultAction":"SCMP_ACT_ALLOW",
+				"architectures":["SCMP_ARCH_X86","SCMP_ARCH_X32","SCMP_ARCH_X86_64","SCMP_ARCH_AARCH64","SCMP_ARCH_ARM"],
+				"syscalls":[{"names":["mkdir"], "action":"SCMP_ACT_ERRNO"}]
+			}'
+
+	declare -A FLAGS=(
+		['REMOVE']=0 # No setting, use built-in default.
+		['EMPTY']=0  # Empty set of flags.
+		['"SECCOMP_FILTER_FLAG_LOG"']=2
+		['"SECCOMP_FILTER_FLAG_SPEC_ALLOW"']=4
+		['"SECCOMP_FILTER_FLAG_TSYNC"']=0 # tsync flag is ignored.
+		['"SECCOMP_FILTER_FLAG_LOG","SECCOMP_FILTER_FLAG_SPEC_ALLOW"']=6
+		['"SECCOMP_FILTER_FLAG_LOG","SECCOMP_FILTER_FLAG_TSYNC"']=2
+		['"SECCOMP_FILTER_FLAG_SPEC_ALLOW","SECCOMP_FILTER_FLAG_TSYNC"']=4
+		['"SECCOMP_FILTER_FLAG_LOG","SECCOMP_FILTER_FLAG_SPEC_ALLOW","SECCOMP_FILTER_FLAG_TSYNC"']=6
 	)
-	for flags in "${SECCOMP_FILTER_FLAGS[@]}"; do
-		update_config '   .process.args = ["/bin/sh", "-c", "mkdir /dev/shm/foo"]
-				| .process.noNewPrivileges = false
-				| .linux.seccomp = {
-					"defaultAction":"SCMP_ACT_ALLOW",
-					"architectures":["SCMP_ARCH_X86","SCMP_ARCH_X32","SCMP_ARCH_X86_64","SCMP_ARCH_AARCH64","SCMP_ARCH_ARM"],
-					"flags":['"${flags}"'],
-					"syscalls":[{"names":["mkdir"], "action":"SCMP_ACT_ERRNO"}]
-				}'
-
-		# This test checks that the flags are accepted without errors but does
-		# not check they are effectively applied
-		runc run test_busybox
+	for key in "${!FLAGS[@]}"; do
+		case "$key" in
+		'REMOVE')
+			update_config ' del(.linux.seccomp.flags)'
+			;;
+		'EMPTY')
+			update_config ' .linux.seccomp.flags = []'
+			;;
+		*)
+			update_config ' .linux.seccomp.flags = [ '"${key}"' ]'
+			;;
+		esac
+
+		runc --debug run test_busybox
 		[ "$status" -ne 0 ]
 		[[ "$output" == *"mkdir:"*"/dev/shm/foo"*"Operation not permitted"* ]]
+
+		# Check the numeric flags value, as printed in the debug log, is as expected.
+		exp="\"seccomp filter flags: ${FLAGS[$key]}\""
+		echo "flags $key, expecting $exp"
+		[[ "$output" == *"$exp"* ]]
 	done
 }