rootless: do not configure additional groups

Additional groups are not allowed in an userNS.

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

Closes: #936
Approved by: rhatdan

libpod/container_internal.go

@@ -1286,7 +1286,7 @@ func (c *Container) generateSpec(ctx context.Context) (*spec.Spec, error) {
 	}
 
 	// Look up and add groups the user belongs to, if a group wasn't directly specified
-	if !strings.Contains(c.config.User, ":") {
+	if !rootless.IsRootless() && !strings.Contains(c.config.User, ":") {
 		groups, err := chrootuser.GetAdditionalGroupsForUser(c.state.Mountpoint, uint64(g.Spec().Process.User.UID))
 		if err != nil && errors.Cause(err) != chrootuser.ErrNoSuchUser {
 			return nil, err

pkg/rootless/rootless_linux.c

@@ -66,6 +66,8 @@ get_cmd_line_args (pid_t pid)
       argc++;
 
   argv = malloc (sizeof (char *) * (argc + 1));
+  if (argv == NULL)
+    return NULL;
   argc = 0;
 
   argv[argc++] = buffer;