linux-kernel - Re: [PATCH] cgroup: fix a race condition in manipulating tsk->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 for Android: free password hash cracker in your pocket

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

Date:	Wed, 16 Apr 2008 21:17:34 -0700
From:	"Paul Menage" <menage@...gle.com>
To:	"Andrew Morton" <akpm@...ux-foundation.org>
Cc:	"Li Zefan" <lizf@...fujitsu.com>,
	"Linus Torvalds" <torvalds@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"Linux Containers" <containers@...ts.linux-foundation.org>,
	"Balbir Singh" <balbir@...ux.vnet.ibm.com>,
	"KAMEZAWA Hiroyuki" <kamezawa.hiroyu@...fujitsu.com>,
	"Paul Jackson" <pj@....com>
Subject: Re: [PATCH] cgroup: fix a race condition in manipulating tsk->cg_list

On Wed, Apr 16, 2008 at 9:11 PM, Andrew Morton
<akpm@...ux-foundation.org> wrote:
>
>  I don't fully understand the race.  Both paths hold css_set_lock.
>
>  Can you describe it in more detail please?

Task A starts exiting, passes the check for unlinking current->cg_list.

Before it completely exits task B does the very first
cgroup_iter_begin() call (via reading a cgroups tasks file) which
links all tasks in to their css_set objects via tsk->cg_list.

Then task A finishes exiting and is freed, but doesn't unlink from the cg_list.

>
>  afacit the task at *p could set PF_EXITING immediately after this code has
>  tested PF_EXITING and then the task at *p could proceed until we hit the
>  same race (whatever that is).

The important fact there is that the task sets PF_EXITING *before* it
checks whether it needs to unlink from current->cg_list.

Paul
--
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/