create: fix writing cidfile when using rootless

prevent opening the same file twice, since we re-exec podman in
rootless mode.  While at it, also solve a possible race between the
check for the file and writing to it.  Another process could have
created the file in the meanwhile and we would just end up overwriting
it.

Signed-off-by: Giuseppe Scrivano <gscrivan@redhat.com>

1 files changed, 11 insertions, 7 deletions

diff --git a/cmd/podman/pod_create.go b/cmd/podman/pod_create.go
index c3a45a093..63fa6b294 100644
--- a/cmd/podman/pod_create.go
+++ b/cmd/podman/pod_create.go
@@ -90,13 +90,17 @@ func podCreateCmd(c *cli.Context) error {
 	}
 	defer runtime.Shutdown(false)
 
-	if c.IsSet("pod-id-file") {
-		if _, err = os.Stat(c.String("pod-id-file")); err == nil {
-			return errors.Errorf("pod id file exists. ensure another pod is not using it or delete %s", c.String("pod-id-file"))
+	var podIdFile *os.File
+	if c.IsSet("pod-id-file") && os.Geteuid() == 0 {
+		podIdFile, err = libpod.OpenExclusiveFile(c.String("pod-id-file"))
+		if err != nil && os.IsExist(err) {
+			return errors.Errorf("pod id file exists. Ensure another pod is not using it or delete %s", c.String("pod-id-file"))
 		}
-		if err = libpod.WriteFile("", c.String("pod-id-file")); err != nil {
-			return errors.Wrapf(err, "unable to write pod id file %s", c.String("pod-id-file"))
+		if err != nil {
+			return errors.Errorf("error opening pod-id-file %s", c.String("pod-id-file"))
 		}
+		defer podIdFile.Close()
+		defer podIdFile.Sync()
 	}
 	if !c.BoolT("infra") && c.IsSet("share") && c.String("share") != "none" && c.String("share") != "" {
 		return errors.Errorf("You cannot share kernel namespaces on the pod level without an infra container")
@@ -137,8 +141,8 @@ func podCreateCmd(c *cli.Context) error {
 		return err
 	}
 
-	if c.IsSet("pod-id-file") {
-		err = libpod.WriteFile(pod.ID(), c.String("pod-id-file"))
+	if podIdFile != nil {
+		_, err = podIdFile.WriteString(pod.ID())
 		if err != nil {
 			logrus.Error(err)
 		}