linux-kernel - [PATCH 0/2] pids: initial fixes, unsafe dereference of the special pids

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Date:	Mon, 24 Mar 2008 21:36:03 +0300
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Pavel Emelyanov <xemul@...nvz.org>,
	Roland McGrath <roland@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: [PATCH 0/2] pids: initial fixes, unsafe dereference of the special pids

Without rcu ot tasklist lock held, it is not safe to dereference the
result of task_session/task_pgrp. Even if the task == current.

Because we can race with another thread doing setpgrp/setsid, and use
the already freed/reused/unmapped memory if preempted.

The problem is old, surprisingly it wasn't noticed before. Fortunately
it is not very serious.

We have a lot of users which should be fixed. This series only fixes
sys_getsid/sys_getpgid syscalls.

Perhaps we can (should) add rcu lock/unlock to task_xxx_vnr(), but I'm
not sure. In any case, I think it is good to factor out pid_vnr() calls
like these patches do.

Oleg.

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