Fix problem copying files when container is in host pid namespace

libpod/container_copy_linux.go

@@ -237,21 +237,32 @@ func (c *Container) joinMountAndExec(ctx context.Context, f func() error) error
 		}
 		defer mountFD.Close()
 
-		pidFD, err := getFD(PIDNS)
+		inHostPidNS, err := c.inHostPidNS()
 		if err != nil {
-			errChan <- err
+			errChan <- errors.Wrap(err, "checking inHostPidNS")
 			return
 		}
-		defer pidFD.Close()
-		if err := unix.Unshare(unix.CLONE_NEWNS); err != nil {
-			errChan <- err
-			return
+		var pidFD *os.File
+		if !inHostPidNS {
+			pidFD, err = getFD(PIDNS)
+			if err != nil {
+				errChan <- err
+				return
+			}
+			defer pidFD.Close()
 		}
-		if err := unix.Setns(int(pidFD.Fd()), unix.CLONE_NEWPID); err != nil {
+
+		if err := unix.Unshare(unix.CLONE_NEWNS); err != nil {
 			errChan <- err
 			return
 		}
 
+		if pidFD != nil {
+			if err := unix.Setns(int(pidFD.Fd()), unix.CLONE_NEWPID); err != nil {
+				errChan <- err
+				return
+			}
+		}
 		if err := unix.Setns(int(mountFD.Fd()), unix.CLONE_NEWNS); err != nil {
 			errChan <- err
 			return

libpod/container_inspect.go

@@ -892,3 +892,26 @@ func (c *Container) generateInspectContainerHostConfig(ctrSpec *spec.Spec, named
 
 	return hostConfig, nil
 }
+
+// Return true if the container is running in the host's PID NS.
+func (c *Container) inHostPidNS() (bool, error) {
+	if c.config.PIDNsCtr != "" {
+		return false, nil
+	}
+	ctrSpec, err := c.specFromState()
+	if err != nil {
+		return false, err
+	}
+	if ctrSpec.Linux != nil {
+		// Locate the spec's PID namespace.
+		// If there is none, it's pid=host.
+		// If there is one and it has a path, it's "ns:".
+		// If there is no path, it's default - the empty string.
+		for _, ns := range ctrSpec.Linux.Namespaces {
+			if ns.Type == spec.PIDNamespace {
+				return false, nil
+			}
+		}
+	}
+	return true, nil
+}

test/e2e/cp_test.go

@@ -91,6 +91,50 @@ var _ = Describe("Podman cp", func() {
 		Expect(roundtripContent).To(Equal(originalContent))
 	})
 
+	// Copy a file to the container, then back to the host in --pid=host
+	It("podman cp --pid=host file", func() {
+		SkipIfRootlessCgroupsV1("Not supported for rootless + CGroupsV1")
+		srcFile, err := ioutil.TempFile("", "")
+		Expect(err).To(BeNil())
+		defer srcFile.Close()
+		defer os.Remove(srcFile.Name())
+
+		originalContent := []byte("podman cp file test")
+		err = ioutil.WriteFile(srcFile.Name(), originalContent, 0644)
+		Expect(err).To(BeNil())
+
+		// Create a container. NOTE that container mustn't be running for copying.
+		session := podmanTest.Podman([]string{"create", "--pid=host", ALPINE, "top"})
+		session.WaitWithDefaultTimeout()
+		Expect(session.ExitCode()).To(Equal(0))
+		name := session.OutputToString()
+
+		session = podmanTest.Podman([]string{"start", name})
+		session.WaitWithDefaultTimeout()
+		Expect(session.ExitCode()).To(Equal(0))
+
+		// The file will now be created (and written to).
+		session = podmanTest.Podman([]string{"cp", srcFile.Name(), name + ":foo"})
+		session.WaitWithDefaultTimeout()
+		Expect(session.ExitCode()).To(Equal(0))
+
+		// Copy FROM the container.
+
+		destFile, err := ioutil.TempFile("", "")
+		Expect(err).To(BeNil())
+		defer destFile.Close()
+		defer os.Remove(destFile.Name())
+
+		session = podmanTest.Podman([]string{"cp", name + ":foo", destFile.Name()})
+		session.WaitWithDefaultTimeout()
+		Expect(session.ExitCode()).To(Equal(0))
+
+		// Now make sure the content matches.
+		roundtripContent, err := ioutil.ReadFile(destFile.Name())
+		Expect(err).To(BeNil())
+		Expect(roundtripContent).To(Equal(originalContent))
+	})
+
 	// Create a symlink in the container, use it as a copy destination and
 	// make sure that the link and the resolved path are accessible and
 	// give the right content.

test/system/065-cp.bats

@@ -130,6 +130,22 @@ load helpers
 }
 
 
+@test "podman cp file from/to host while --pid=host" {
+    if is_rootless && ! is_cgroupsv2; then
+        skip "'podman cp --pid=host' (rootless) only works with cgroups v2"
+    fi
+
+    srcdir=$PODMAN_TMPDIR/cp-pid-equals-host
+    mkdir -p $srcdir
+    touch $srcdir/hostfile
+
+    run_podman run --pid=host -d --name cpcontainer $IMAGE sleep infinity
+    run_podman cp $srcdir/hostfile cpcontainer:/tmp/hostfile
+    run_podman cp cpcontainer:/tmp/hostfile $srcdir/hostfile1
+    run_podman kill cpcontainer
+    run_podman rm -f cpcontainer
+}
+
 @test "podman cp file from container to host" {
     srcdir=$PODMAN_TMPDIR/cp-test-file-ctr-to-host
     mkdir -p $srcdir