[3.8.y.z extended stable] Patch "pid_namespace: pidns_get() should check task_active_pid_ns() != NULL" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    pid_namespace: pidns_get() should check task_active_pid_ns() != NULL

to the linux-3.8.y-queue branch of the 3.8.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.8.y-queue

This patch is scheduled to be released in version 3.8.13.22.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.8.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From df77c7222da0df13dcdca40e0a4f3aa4daf6b66c Mon Sep 17 00:00:00 2001
From: Oleg Nesterov <oleg at redhat.com>
Date: Wed, 2 Apr 2014 17:45:05 +0200
Subject: pid_namespace: pidns_get() should check task_active_pid_ns() != NULL

commit d23082257d83e4bc89727d5aedee197e907999d2 upstream.

pidns_get()->get_pid_ns() can hit ns == NULL. This task_struct can't
go away, but task_active_pid_ns(task) is NULL if release_task(task)
was already called. Alternatively we could change get_pid_ns(ns) to
check ns != NULL, but it seems that other callers are fine.

Signed-off-by: Oleg Nesterov <oleg at redhat.com>
Cc: Eric W. Biederman ebiederm at xmission.com>
Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 kernel/pid_namespace.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c
index bea15bd..7d40b94 100644
--- a/kernel/pid_namespace.c
+++ b/kernel/pid_namespace.c
@@ -314,7 +314,9 @@ static void *pidns_get(struct task_struct *task)
 	struct pid_namespace *ns;

 	rcu_read_lock();
-	ns = get_pid_ns(task_active_pid_ns(task));
+	ns = task_active_pid_ns(task);
+	if (ns)
+		get_pid_ns(ns);
 	rcu_read_unlock();

 	return ns;
--
1.9.1