linux-kernel - Re: [PATCH] epoll: fix use-after-free in eventpoll_release

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Date:	Tue, 17 Jun 2014 09:50:42 +0400
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	Konstantin Khlebnikov <koct9i@...il.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Sasha Levin <sasha.levin@...cle.com>,
	Jason Baron <jbaron@...mai.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Stable <stable@...r.kernel.org>
Subject: Re: [PATCH] epoll: fix use-after-free in eventpoll_release_file

On Tue, Jun 17, 2014 at 06:58:05AM +0400, Konstantin Khlebnikov wrote:
> This fixes use-after-free of epi->fllink.next inside list loop macro.
> This loop actually releases elements in the body. List is rcu-protected
> but here we cannot hold rcu_read_lock because we need to lock mutex inside.
> 
> Obvious solution is to use list_for_each_entry_safe(). RCU-ness isn't essential
> because nobody can change this list under us, it's final fput for this file.
> 
> Bug is here since ae10b2b4eb01bedc91d29d5c5bb9e416fd806c40
> ("epoll: optimize EPOLL_CTL_DEL using rcu")
> 
> Signed-off-by: Konstantin Khlebnikov <koct9i@...il.com>
> Reported-by: Cyrill Gorcunov <gorcunov@...nvz.org>
> Cc: Stable <stable@...r.kernel.org> # 3.13+
> Cc: Sasha Levin <sasha.levin@...cle.com>
> Cc: Jason Baron <jbaron@...mai.com>
Acked-by: Cyrill Gorcunov <gorcunov@...nvz.org>
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