dmz: remove SELinux special-casing

Now that runc-dmz is opt-in, we no longer need to try to detect whether
SELinux would cause issues for us. We can also remove the
special-purpose build-tag we added.

Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>

tests/integration/helpers.bash

@@ -538,6 +538,20 @@ function requires() {
 	done
 }
 
+# Allow a test to specify that it will not work properly on a given OS. The
+# fingerprint for the OS used for this test is $ID-$VERSION_ID, using the
+# variables in /etc/os-release. The arguments are regular expressions, and any
+# match will cause the test to be skipped.
+function exclude_os() {
+	local host
+	host="$(sh -c '. /etc/os-release ; echo "$ID-$VERSION_ID"')"
+	for bad_os in "$@"; do
+		if [[ "$host" =~ ^$bad_os$ ]]; then
+			skip "test doesn't work on $bad_os"
+		fi
+	done
+}
+
 # Retry a command $1 times until it succeeds. Wait $2 seconds between retries.
 function retry() {
 	local attempts=$1

tests/integration/run.bats

@@ -128,6 +128,10 @@ function teardown() {
 }
 
 @test "RUNC_DMZ=true runc run [runc-dmz]" {
+	# centos-7 has an outdated container-selinux (<2.224.0) which means
+	# runc-dmz won't work.
+	exclude_os centos-7
+
 	RUNC_DMZ=true runc --debug run test_hello
 	[ "$status" -eq 0 ]
 	[[ "$output" = *"Hello World"* ]]
@@ -136,6 +140,10 @@ function teardown() {
 }
 
 @test "RUNC_DMZ=true runc run [cap_sys_ptrace -> /proc/self/exe clone]" {
+	# centos-7 has an outdated container-selinux (<2.224.0) which means
+	# runc-dmz won't work.
+	exclude_os centos-7
+
 	# Add CAP_SYS_PTRACE to the bounding set, the minimum needed to indicate a
 	# container process _could_ get CAP_SYS_PTRACE.
 	update_config '.process.capabilities.bounding += ["CAP_SYS_PTRACE"]'
@@ -232,6 +240,10 @@ function teardown() {
 }
 
 @test "RUNC_DMZ=true runc run [exec error]" {
+	# centos-7 has an outdated container-selinux (<2.224.0) which means
+	# runc-dmz won't work.
+	exclude_os centos-7
+
 	cat <<EOF >rootfs/run.sh
 #!/mmnnttbb foo bar
 sh

tests/integration/selinux.bats

@@ -40,6 +40,10 @@ function teardown() {
 
 # https://github.com/opencontainers/runc/issues/4057
 @test "runc run (custom selinux label, RUNC_DMZ=true)" {
+	# centos-7 has an outdated container-selinux (<2.224.0) which means
+	# runc-dmz won't work.
+	exclude_os centos-7
+
 	update_config '	  .process.selinuxLabel |= "system_u:system_r:container_t:s0:c4,c5"
 			| .process.args = ["/bin/true"]'
 	RUNC_DMZ=true runc run tst