Patch "netfilter: ipset: Fix sleeping memory allocation in atomic context" has been added to the 4.2-stable tree

This is a note to let you know that I've just added the patch titled

netfilter: ipset: Fix sleeping memory allocation in atomic context

to the 4.2-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
netfilter-ipset-fix-sleeping-memory-allocation-in-atomic-context.patch
and it can be found in the queue-4.2 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Nikolay Borisov <[email protected]>
Date: Fri, 16 Oct 2015 09:40:28 +0300
Subject: netfilter: ipset: Fix sleeping memory allocation in atomic context

From: Nikolay Borisov <[email protected]>

commit 00db674bedd68ff8b5afae9030ff5e04d45d1b4a upstream.

Commit 00590fdd5be0 introduced RCU locking in list type and in doing so introduced a memory allocation in list_set_add, which is done in an atomic context, due to the fact that ipset rcu list modifications are serialised with a spin lock. The reason why we can't use a mutex is that in addition to modifying the list with ipset commands, it's also being modified when a particular ipset rule timeout expires aka garbage collection. This gc is triggered from set_cleanup_entries, which in turn is invoked from a timer thus requiring the lock to be bh-safe.

Concretely the following call chain can lead to "sleeping function called in atomic context" splat:
call_ad -> list_set_uadt -> list_set_uadd -> kzalloc(, GFP_KERNEL). And since GFP_KERNEL allows initiating direct reclaim thus potentially sleeping in the allocation path.

To fix the issue change the allocation type to GFP_ATOMIC, to correctly reflect that it is occuring in an atomic context.

---
 net/netfilter/ipset/ip_set_list_set.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

@@ -297,7 +297,7 @@ list_set_uadd(struct ip_set *set, void *
 	      ip_set_timeout_expired(ext_timeout(n, set))))
 		n =  NULL;
 
-	e = kzalloc(set->dsize, GFP_KERNEL);
+	e = kzalloc(set->dsize, GFP_ATOMIC);
 	if (!e)
 		return -ENOMEM;
 	e->id = d->id;

Patches currently in stable-queue which might be from [email protected] are

queue-4.2/netfilter-ipset-fix-sleeping-memory-allocation-in-atomic-context.patch