From: Cedric Le Goater <clg@fr.ibm.com>

get_user_ns() returns NULL when CONFIG_USER_NS=n and this breaks
sigio_perm() which does not expect NULL values for ->user_ns.

I would fix this with the following patch.

Signed-off-by: Cedric Le Goater <clg@fr.ibm.com>
Cc: Serge E. Hallyn <serue@us.ibm.com>
Cc: Herbert Poetzl <herbert@13thfloor.at>
Cc: Kirill Korotaev <dev@sw.ru>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
---

 include/linux/user_namespace.h |    2 +-
 1 files changed, 1 insertion(+), 1 deletion(-)

diff -puN include/linux/user_namespace.h~user_ns-handle-file-sigio-fix include/linux/user_namespace.h
--- a/include/linux/user_namespace.h~user_ns-handle-file-sigio-fix
+++ a/include/linux/user_namespace.h
@@ -48,7 +48,7 @@ static inline int clone_mnt_userns_permi
 
 static inline struct user_namespace *get_user_ns(struct user_namespace *ns)
 {
-	return NULL;
+	return &init_user_ns;
 }
 
 static inline int copy_user_ns(int flags, struct task_struct *tsk)
_