podman: allow to specify the UTS namespace to join

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

Closes: #1145
Approved by: rhatdan

cmd/podman/create.go

@@ -389,7 +389,7 @@ func parseCreateOpts(ctx context.Context, c *cli.Context, runtime *libpod.Runtim
 	}
 
 	utsMode := container.UTSMode(c.String("uts"))
-	if !utsMode.Valid() {
+	if !cc.IsNS(string(utsMode)) && !utsMode.Valid() {
 		return nil, errors.Errorf("--uts %q is not valid", c.String("uts"))
 	}
 	ipcMode := container.IpcMode(c.String("ipc"))

docs/podman-create.1.md

@@ -589,6 +589,7 @@ Set the usernamespace mode for the container. The use of userns is disabled by d
 
 Set the UTS mode for the container
     **host**: use the host's UTS namespace inside the container.
+    **ns**: specify the usernamespace to use.
     Note: the host mode gives the container access to changing the host's hostname and is therefore considered insecure.
 
 **-v**|**--volume**[=*[HOST-DIR:CONTAINER-DIR[:OPTIONS]]*]

docs/podman-run.1.md

@@ -620,6 +620,7 @@ Set the usernamespace mode for the container. The use of userns is disabled by d
 Set the UTS mode for the container
 
 `host`: use the host's UTS namespace inside the container.
+`ns`: specify the usernamespace to use.
 
 **NOTE**: the host mode gives the container access to changing the host's hostname and is therefore considered insecure.
 

pkg/spec/spec.go

@@ -369,6 +369,9 @@ func addNetNS(config *CreateConfig, g *generate.Generator) error {
 
 func addUTSNS(config *CreateConfig, g *generate.Generator) error {
 	utsMode := config.UtsMode
+	if IsNS(string(utsMode)) {
+		return g.AddOrReplaceLinuxNamespace(string(spec.UTSNamespace), NS(string(utsMode)))
+	}
 	if utsMode.IsHost() {
 		return g.RemoveLinuxNamespace(spec.UTSNamespace)
 	}