ACK: [maverick, maverick/ti-omap4, natty, natty/ti-omap4, oneiric, precise CVE 1/1] mm: memcg: Correct unregistring of events attached to the same eventfd

[Colin Ian King]

On 12/03/12 11:22, Andy Whitcroft wrote:
> From: Anton Vorontsov<anton.vorontsov at linaro.org>
>
> There is an issue when memcg unregisters events that were attached to
> the same eventfd:
>
> - On the first call mem_cgroup_usage_unregister_event() removes all
>    events attached to a given eventfd, and if there were no events left,
>    thresholds->primary would become NULL;
>
> - Since there were several events registered, cgroups core will call
>    mem_cgroup_usage_unregister_event() again, but now kernel will oops,
>    as the function doesn't expect that threshold->primary may be NULL.
>
> That's a good question whether mem_cgroup_usage_unregister_event()
> should actually remove all events in one go, but nowadays it can't
> do any better as cftype->unregister_event callback doesn't pass
> any private event-associated cookie. So, let's fix the issue by
> simply checking for threshold->primary.
>
> FWIW, w/o the patch the following oops may be observed:
>
>   BUG: unable to handle kernel NULL pointer dereference at 0000000000000004
>   IP: [<ffffffff810be32c>] mem_cgroup_usage_unregister_event+0x9c/0x1f0
>   Pid: 574, comm: kworker/0:2 Not tainted 3.3.0-rc4+ #9 Bochs Bochs
>   RIP: 0010:[<ffffffff810be32c>]  [<ffffffff810be32c>] mem_cgroup_usage_unregister_event+0x9c/0x1f0
>   RSP: 0018:ffff88001d0b9d60  EFLAGS: 00010246
>   Process kworker/0:2 (pid: 574, threadinfo ffff88001d0b8000, task ffff88001de91cc0)
>   Call Trace:
>    [<ffffffff8107092b>] cgroup_event_remove+0x2b/0x60
>    [<ffffffff8103db94>] process_one_work+0x174/0x450
>    [<ffffffff8103e413>] worker_thread+0x123/0x2d0
>
> Cc: stable<stable at vger.kernel.org>
> Signed-off-by: Anton Vorontsov<anton.vorontsov at linaro.org>
> Acked-by: KAMEZAWA Hiroyuki<kamezawa.hiroyu at jp.fujitsu.com>
> Cc: Kirill A. Shutemov<kirill at shutemov.name>
> Cc: Michal Hocko<mhocko at suse.cz>
> Signed-off-by: Linus Torvalds<torvalds at linux-foundation.org>
>
> (cherry picked from commit 371528caec553785c37f73fa3926ea0de84f986f)
> CVE-2012-1146
> BugLink: http://bugs.launchpad.net/bugs/952828
> Signed-off-by: Andy Whitcroft<apw at canonical.com>
> ---
>   mm/memcontrol.c |    5 ++++-
>   1 files changed, 4 insertions(+), 1 deletions(-)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 20a8193..ebca7c0 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -3647,6 +3647,9 @@ static void mem_cgroup_usage_unregister_event(struct cgroup *cgrp,
>   	 */
>   	BUG_ON(!thresholds);
>
> +	if (!thresholds->primary)
> +		goto unlock;
> +
>   	usage = mem_cgroup_usage(memcg, type == _MEMSWAP);
>
>   	/* Check if a threshold crossed before removing */
> @@ -3695,7 +3698,7 @@ swap_buffers:
>
>   	/* To be sure that nobody uses thresholds */
>   	synchronize_rcu();
> -
> +unlock:
>   	mutex_unlock(&memcg->thresholds_lock);
>   }
>

Upstream patch, looks sane to me, ACK.

Acked-by: Colin Ian King <colin.king at canonical.com>