linux-kernel - Re: [PATCH] fix the racy check_hung_uninterruptible_tasks()->rcu_lock

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

Message-ID: <20100618203854.GW915@google.com>
Date:	Fri, 18 Jun 2010 13:38:54 -0700
From:	Mandeep Singh Baines <msb@...gle.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Don Zickus <dzickus@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...e.hu>,
	Jerome Marchand <jmarchan@...hat.com>,
	Roland McGrath <roland@...hat.com>,
	linux-kernel@...r.kernel.org, stable@...nel.org
Subject: Re: [PATCH] fix the racy
	check_hung_uninterruptible_tasks()->rcu_lock_break() logic

Oleg Nesterov (oleg@...hat.com) wrote:
> check_hung_uninterruptible_tasks()->rcu_lock_break() introduced by
> "softlockup: check all tasks in hung_task" commit ce9dbe24 looks
> absolutely wrong.
> 
> 	- rcu_lock_break() does put_task_struct(). If the task has exited
> 	  it is not safe to even read its ->state, nothing protects this
> 	  task_struct.
> 
> 	- The TASK_DEAD checks are wrong too. Contrary to the comment, we
> 	  can't use it to check if the task was unhashed. It can be unhashed
> 	  without TASK_DEAD, or it can be valid with TASK_DEAD.
> 
> 	  For example, an autoreaping task can do release_task(current)
> 	  long before it sets TASK_DEAD in do_exit().
> 
> 	  Or, a zombie task can have ->state == TASK_DEAD but release_task()
> 	  was not called, and in this case we must not break the loop.
> 
> Change this code to check pid_alive() instead, and do this before we
> drop the reference to the task_struct.
> 
> Signed-off-by: Oleg Nesterov <oleg@...hat.com>
> ---

Acked-by: Mandeep Singh Baines <msb@...gle.com>
--
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/