fix: improve userns validation when joining pods

- remove old CLI validation that only checked --pod flag
- add validation in namespaces.go to catch all paths (cli, quadlet, api)
- block userns mixing for all pods with infra, not just ipc/net
- update error message to be clearer
- fix test cleanup to use PodmanExitCleanly()
- use dynamic pod names in system tests to avoid conflicts

fixes #26848

Signed-off-by: 0xdvc <neilohene@gmail.com>

Author: 0xDVC

cmd/podman/containers/create.go

@@ -308,10 +308,6 @@ func CreateInit(c *cobra.Command, vals entities.ContainerCreateOptions, isInfra
 		if c.Flag("cgroups").Changed && vals.CgroupsMode == "split" && registry.IsRemote() {
 			return vals, fmt.Errorf("the option --cgroups=%q is not supported in remote mode", vals.CgroupsMode)
 		}
-
-		if c.Flag("pod").Changed && !strings.HasPrefix(c.Flag("pod").Value.String(), "new:") && c.Flag("userns").Changed {
-			return vals, errors.New("--userns and --pod cannot be set together")
-		}
 	}
 	if c.Flag("shm-size").Changed {
 		vals.ShmSize = c.Flag("shm-size").Value.String()

pkg/specgen/generate/namespaces.go

@@ -21,6 +21,20 @@ import (
 
 const host = "host"
 
+// userNSConflictsWithPod returns an error if the user namespace mode
+// conflicts with pod namespace sharing requirements.
+// Containers in a pod must use the same user namespace to avoid ownership and
+// capability issues with shared resources.
+func userNSConflictsWithPod(pod *libpod.Pod, mode specgen.NamespaceMode) error {
+	if pod != nil && pod.HasInfraContainer() {
+		// FromPod mode is allowed - container inherits from pod
+		if mode != specgen.FromPod {
+			return fmt.Errorf("cannot set user namespace mode when joining pod with infra container: %w", define.ErrInvalidArg)
+		}
+	}
+	return nil
+}
+
 // Get the default namespace mode for any given namespace type.
 func GetDefaultNamespaceMode(nsType string, cfg *config.Config, pod *libpod.Pod) (specgen.Namespace, error) {
 	// The default for most is private
@@ -211,7 +225,11 @@ func namespaceOptions(s *specgen.SpecGenerator, rt *libpod.Runtime, pod *libpod.
 		}
 	}
 
-	// User
+	// Validate that user namespace mode is compatible with pod.
+	if err := userNSConflictsWithPod(pod, s.UserNS.NSMode); err != nil {
+		return nil, err
+	}
+
 	switch s.UserNS.NSMode {
 	case specgen.KeepID:
 		opts, err := namespaces.UsernsMode(s.UserNS.String()).GetKeepIDOptions()
@@ -247,6 +265,10 @@ func namespaceOptions(s *specgen.SpecGenerator, rt *libpod.Runtime, pod *libpod.
 			return nil, fmt.Errorf("looking up container to share user namespace with: %w", err)
 		}
 		toReturn = append(toReturn, libpod.WithUserNSFrom(userCtr))
+	case specgen.Private:
+	case specgen.Auto:
+	case specgen.NoMap:
+	case specgen.Path:
 	}
 
 	// This wipes the UserNS settings that get set from the infra container
@@ -255,8 +277,6 @@ func namespaceOptions(s *specgen.SpecGenerator, rt *libpod.Runtime, pod *libpod.
 	if s.IDMappings != nil {
 		if pod == nil {
 			toReturn = append(toReturn, libpod.WithIDMappings(*s.IDMappings))
-		} else if pod.HasInfraContainer() && (len(s.IDMappings.UIDMap) > 0 || len(s.IDMappings.GIDMap) > 0) {
-			return nil, fmt.Errorf("cannot specify a new uid/gid map when entering a pod with an infra container: %w", define.ErrInvalidArg)
 		}
 	}
 	if s.User != "" {

test/e2e/create_test.go

@@ -681,13 +681,14 @@ var _ = Describe("Podman create", func() {
 		create := podmanTest.Podman([]string{"create", "--uidmap", "0:1000:1000", "--pod", "new:testing123", ALPINE})
 		create.WaitWithDefaultTimeout()
 		Expect(create).ShouldNot(ExitCleanly())
-		Expect(create.ErrorToString()).To(ContainSubstring("cannot specify a new uid/gid map when entering a pod with an infra container"))
+		Expect(create.ErrorToString()).To(ContainSubstring("cannot set user namespace mode when joining pod with infra container"))
+
+		podmanTest.PodmanExitCleanly("pod", "rm", "-f", "testing123")
 
 		create = podmanTest.Podman([]string{"create", "--gidmap", "0:1000:1000", "--pod", "new:testing1234", ALPINE})
 		create.WaitWithDefaultTimeout()
 		Expect(create).ShouldNot(ExitCleanly())
-		Expect(create.ErrorToString()).To(ContainSubstring("cannot specify a new uid/gid map when entering a pod with an infra container"))
-
+		Expect(create.ErrorToString()).To(ContainSubstring("cannot set user namespace mode when joining pod with infra container"))
 	})
 
 	It("podman create --chrootdirs inspection test", func() {

test/e2e/pod_create_test.go

@@ -804,7 +804,7 @@ ENTRYPOINT ["sleep","99999"]
 		// fail if --pod and --userns set together
 		session = podmanTest.Podman([]string{"run", "--pod", podName, "--userns", "keep-id", ALPINE, "id", "-u"})
 		session.WaitWithDefaultTimeout()
-		Expect(session).Should(ExitWithError(125, "--userns and --pod cannot be set together"))
+		Expect(session).Should(ExitWithError(125, "cannot set user namespace mode when joining pod with infra container"))
 	})
 
 	It("podman pod create with --userns=keep-id can add users", func() {

test/system/620-option-conflicts.bats

@@ -14,7 +14,6 @@ load helpers
 create,run        | --cpu-period=1 | --cpus=2               | $IMAGE
 create,run        | --cpu-quota=1  | --cpus=2               | $IMAGE
 create,run        | --no-hosts     | --add-host=foo:1.1.1.1 | $IMAGE
-create,run        | --userns=bar   | --pod=foo              | $IMAGE
 container cleanup | --all          | --exec=foo
 container cleanup | --exec=foo     | --rmi                  | foo
 "
@@ -48,6 +47,14 @@ container cleanup | --exec=foo     | --rmi                  | foo
                "podman $cmd --platform + --$opt"
         done
     done
+
+    # --userns and --pod have a different error message format
+    podname=p-$(safename)
+    run_podman pod create --name $podname
+    run_podman 125 run --uidmap=0:1000:1000 --pod=$podname $IMAGE true
+    is "$output" "Error: cannot set user namespace mode when joining pod with infra container: invalid argument" \
+       "podman run --uidmap + --pod"
+    run_podman pod rm -f $podname
 }