From patchwork Mon Mar 12 11:22:11 2012 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Subject: [maverick, maverick/ti-omap4, natty, natty/ti-omap4, oneiric, precise, CVE, 1/1] mm: memcg: Correct unregistring of events attached to the same eventfd Date: Mon, 12 Mar 2012 01:22:11 -0000 From: Andy Whitcroft X-Patchwork-Id: 146060 Message-Id: <1331551332-13550-2-git-send-email-apw@canonical.com> To: kernel-team@lists.ubuntu.com Cc: Andy Whitcroft From: Anton Vorontsov 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: [] mem_cgroup_usage_unregister_event+0x9c/0x1f0 Pid: 574, comm: kworker/0:2 Not tainted 3.3.0-rc4+ #9 Bochs Bochs RIP: 0010:[] [] mem_cgroup_usage_unregister_event+0x9c/0x1f0 RSP: 0018:ffff88001d0b9d60 EFLAGS: 00010246 Process kworker/0:2 (pid: 574, threadinfo ffff88001d0b8000, task ffff88001de91cc0) Call Trace: [] cgroup_event_remove+0x2b/0x60 [] process_one_work+0x174/0x450 [] worker_thread+0x123/0x2d0 Cc: stable Signed-off-by: Anton Vorontsov Acked-by: KAMEZAWA Hiroyuki Cc: Kirill A. Shutemov Cc: Michal Hocko Signed-off-by: Linus Torvalds (cherry picked from commit 371528caec553785c37f73fa3926ea0de84f986f) CVE-2012-1146 BugLink: http://bugs.launchpad.net/bugs/952828 Signed-off-by: Andy Whitcroft Acked-by: Colin Ian King --- 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); }