[PATCH] user namespace: fix copy_user_ns return value

[Serge E . Hallyn]

When a CONFIG_USER_NS=n and a user tries to unshare some
namespace other than the user namespace, the dummy
copy_user_ns returns NULL rather than the old_ns.  This
value then gets assigned to task->nsproxy->user_ns, so
that a subsequent setuid, which uses task->nsproxy->user_ns,
causes a NULL pointer deref.

Fix this by returning old_ns.

Signed-off-by: Serge E. Hallyn <serue@xxxxxxxxxx>
---
 include/linux/user_namespace.h |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
index bb32057..1101b0c 100644
--- a/include/linux/user_namespace.h
+++ b/include/linux/user_namespace.h
@@ -49,7 +49,7 @@ static inline struct user_namespace *copy_user_ns(int flags,
 	if (flags & CLONE_NEWUSER)
 		return ERR_PTR(-EINVAL);
 
-	return NULL;
+	return old_ns;
 }
 
 static inline void put_user_ns(struct user_namespace *ns)
-- 
1.5.1.1.GIT

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