Fix problem copying files when container is in host pid namespace

When attempting to copy files into and out of running containers
within the host pidnamespace, the code was attempting to join the
host pidns again, and getting an error. This was causing the podman
cp command to fail. Since we are already in the host pid namespace,
we should not be attempting to join.  This PR adds a check to see if
the container is in NOT host pid namespace, and only then attempts to
join.

Fixes: https://github.com/containers/podman/issues/9985

Signed-off-by: Daniel J Walsh <dwalsh@redhat.com>

2 files changed, 41 insertions, 7 deletions

diff --git a/libpod/container_copy_linux.go b/libpod/container_copy_linux.go
index 5c275c641..0ab322829 100644
--- a/libpod/container_copy_linux.go
+++ b/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
diff --git a/libpod/container_inspect.go b/libpod/container_inspect.go
index 5b2103c92..b38c35697 100644
--- a/libpod/container_inspect.go
+++ b/libpod/container_inspect.go
@@ -890,3 +890,26 @@ 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
+}