[JENKINS-64608] Fix cgroup v2 detection of Docker CLI running inside a container

src/main/java/org/jenkinsci/plugins/docker/workflow/client/DockerClient.java

@@ -36,9 +36,12 @@
 import java.io.BufferedReader;
 import java.io.ByteArrayOutputStream;
 import java.io.IOException;
+import java.io.InputStream;
+import java.io.InputStreamReader;
 import java.io.Reader;
 import java.io.StringReader;
 import java.nio.charset.Charset;
+import java.nio.charset.StandardCharsets;
 import java.text.ParseException;
 import java.text.SimpleDateFormat;
 import java.util.ArrayList;
@@ -336,6 +339,8 @@ public String whoAmI() throws IOException, InterruptedException {
 
     }
 
+    private static final Pattern hostnameMount = Pattern.compile("/containers/([a-z0-9]{64})/hostname");
+
     /**
      * Checks if this {@link DockerClient} instance is running inside a container and returns the id of the container
      * if so.
@@ -349,10 +354,26 @@ public Optional<String> getContainerIdIfContainerized() throws IOException, Inte
             return Optional.absent();
         }
         FilePath cgroupFile = node.createPath("/proc/self/cgroup");
-        if (cgroupFile == null || !cgroupFile.exists()) {
-            return Optional.absent();
+        if (cgroupFile != null && cgroupFile.exists()) {
+            Optional<String> containerId = ControlGroup.getContainerId(cgroupFile);
+            if (containerId.isPresent()) {
+                return containerId;
+            }
+        }
+        // cgroup v2
+        FilePath mountInfo = node.createPath("/proc/1/mountinfo");
+        if (mountInfo != null && mountInfo.exists()) {
+            try (InputStream is = mountInfo.read(); Reader r = new InputStreamReader(is, StandardCharsets.UTF_8); BufferedReader br = new BufferedReader(r)) {
+                String line;
+                while ((line = br.readLine()) != null) {
+                    Matcher m = hostnameMount.matcher(line);
+                    if (m.find()) {
+                        return Optional.of(m.group(1));
+                    }
+                }
+            }
         }
-        return ControlGroup.getContainerId(cgroupFile);
+        return Optional.absent();
     }
 
     public ContainerRecord getContainerRecord(@NonNull EnvVars launchEnv, String containerId) throws IOException, InterruptedException {

src/test/java/org/jenkinsci/plugins/docker/workflow/WithContainerStepTest.java

@@ -32,9 +32,11 @@
 import hudson.model.FileParameterValue;
 import hudson.model.Result;
 import hudson.model.TaskListener;
+import hudson.slaves.DumbSlave;
 import hudson.tools.ToolProperty;
 import hudson.util.ArgumentListBuilder;
 import hudson.util.Secret;
+import hudson.util.StreamTaskListener;
 import java.io.File;
 import java.util.Collection;
 import java.util.Collections;
@@ -48,6 +50,7 @@
 import org.apache.commons.fileupload.FileItem;
 import org.apache.commons.io.FileUtils;
 import org.hamcrest.Matchers;
+import static org.hamcrest.Matchers.is;
 import org.jenkinsci.lib.configprovider.ConfigProvider;
 import org.jenkinsci.lib.configprovider.model.Config;
 import org.jenkinsci.plugins.configfiles.custom.CustomConfig;
@@ -66,6 +69,7 @@
 import org.jenkinsci.plugins.workflow.steps.SynchronousNonBlockingStepExecution;
 import org.jenkinsci.plugins.workflow.test.steps.SemaphoreStep;
 import org.junit.Assume;
+import static org.junit.Assume.assumeTrue;
 import org.junit.ClassRule;
 import org.junit.Ignore;
 import org.junit.Test;
@@ -76,6 +80,7 @@
 import org.jvnet.hudson.test.Issue;
 import org.jvnet.hudson.test.LoggerRule;
 import org.jvnet.hudson.test.RestartableJenkinsRule;
+import org.jvnet.hudson.test.SimpleCommandLauncher;
 import org.jvnet.hudson.test.TestExtension;
 import org.kohsuke.stapler.DataBoundConstructor;
 
@@ -455,4 +460,35 @@ private static final class Execution extends SynchronousNonBlockingStepExecution
         }
     }
 
+    @Issue("JENKINS-64608")
+    @Test public void runningInsideContainer() throws Throwable {
+        story.then(r -> {
+            DockerTestUtil.assumeDocker();
+            assumeTrue("have docker.sock", new File("/var/run/docker.sock").exists());
+            TaskListener taskListener = StreamTaskListener.fromStderr();
+            Launcher.LocalLauncher launcher = new Launcher.LocalLauncher(taskListener);
+            int status = launcher.launch().stdout(taskListener).
+                pwd(new File(WithContainerStepTest.class.getResource("agent-with-docker/Dockerfile").toURI()).getParentFile()).
+                cmds(DockerTool.getExecutable(null, null, null, null), "build", "-t", "agent-with-docker", ".").
+                start().
+                joinWithTimeout(DockerClient.CLIENT_TIMEOUT, TimeUnit.SECONDS, taskListener);
+            Assume.assumeThat("Built agent-with-docker image", status, is(0));
+            DumbSlave s = new DumbSlave("dockerized", "/home/jenkins/agent",
+                new SimpleCommandLauncher("docker run -i --rm --init -v /var/run/docker.sock:/var/run/docker.sock agent-with-docker java -jar /usr/share/jenkins/agent.jar"));
+            r.jenkins.addNode(s);
+            r.waitOnline(s);
+            WorkflowJob p = r.jenkins.createProject(WorkflowJob.class, "p");
+            p.setDefinition(new CpsFlowDefinition(
+                "node('dockerized') {\n" +
+                "  sh 'which docker && docker version'\n" +
+                "  withDockerContainer('httpd:2.4.12') {\n" +
+                "    sh 'cp /usr/local/apache2/conf/extra/httpd-userdir.conf .; ls -la'\n" +
+                "  }\n" +
+                "  sh 'ls -la; cat *.conf'\n" +
+                "}", true));
+            WorkflowRun b = r.buildAndAssertSuccess(p);
+            r.assertLogContains("dockerized seems to be running inside container ", b);
+        });
+    }
+
 }

src/test/resources/org/jenkinsci/plugins/docker/workflow/agent-with-docker/Dockerfile

@@ -0,0 +1,8 @@
+FROM jenkins/agent:4.10-5-jdk11
+USER root
+RUN cat /etc/os-release
+# TODO https://github.com/moby/moby/issues/15717 alas; no curl or wget in image
+ADD https://download.docker.com/linux/debian/dists/bullseye/pool/stable/amd64/docker-ce-cli_20.10.20~3-0~debian-bullseye_amd64.deb /tmp/docker.deb
+RUN dpkg -i /tmp/docker.deb
+RUN docker version || :
+# Stay as root, so we can access docker.sock