linux-kernel - [PATCH cgroup/for-3.14-fixes] cgroup: update cgroup_enable_task_cg

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Date:	Thu, 13 Feb 2014 13:29:31 -0500
From:	Tejun Heo <tj@...nel.org>
To:	Li Zefan <lizefan@...wei.com>
Cc:	cgroups@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH cgroup/for-3.14-fixes] cgroup: update
 cgroup_enable_task_cg_lists() to grab siglock

Currently, there's nothing preventing cgroup_enable_task_cg_lists()
from missing set PF_EXITING and race against cgroup_exit().  Depending
on the timing, cgroup_exit() may finish with the task still linked on
css_set leading to list corruption.  Fix it by grabbing siglock in
cgroup_enable_task_cg_lists() so that PF_EXITING is guaranteed to be
visible.

This whole on-demand cg_list optimization is extremely fragile and has
ample possibility to lead to bugs which can cause things like
once-a-year oops during boot.  I'm wondering whether the better
approach would be just adding "cgroup_disable=all" handling which
disables the whole cgroup rather than tempting fate with this
on-demand craziness.

Signed-off-by: Tejun Heo <tj@...nel.org>
Cc: stable@...r.kernel.org
---
 kernel/cgroup.c |    5 +++++
 1 file changed, 5 insertions(+)

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 68d8710..105f273 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -2905,9 +2905,14 @@ static void cgroup_enable_task_cg_lists(void)
 		 * We should check if the process is exiting, otherwise
 		 * it will race with cgroup_exit() in that the list
 		 * entry won't be deleted though the process has exited.
+		 * Do it while holding siglock so that we don't end up
+		 * racing against cgroup_exit().
 		 */
+		spin_lock_irq(&p->sighand->siglock);
 		if (!(p->flags & PF_EXITING) && list_empty(&p->cg_list))
 			list_add(&p->cg_list, &task_css_set(p)->tasks);
+		spin_unlock_irq(&p->sighand->siglock);
+
 		task_unlock(p);
 	} while_each_thread(g, p);
 	read_unlock(&tasklist_lock);
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/