linux-kernel - Re: 2.6.27-rc7-sha1: EIP at proc_sys

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Date:	Sun, 28 Sep 2008 13:59:33 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Hugh Dickins <hugh@...itas.com>
cc:	Al Viro <viro@...IV.linux.org.uk>,
	Alexey Dobriyan <adobriyan@...il.com>, ebiederm@...ssion.com,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: 2.6.27-rc7-sha1: EIP at proc_sys_compare+0x36/0x50

On Sun, 28 Sep 2008, Linus Torvalds wrote:
> 
> NOTE! Totally untested patch! It looks sane and really obvious, but maybe 
> it has some insane and non-obvious bug.

Oh. I think I see at least a _potential_ insane and non-obvious bug: if 
somebody actually is going to do a __d_drop() _inside_ their d_compare(), 
this would fail horribly because we now assume that the dentry is still 
fine, since we held d_lock.

Of course, I think that would be very very buggy of a filesystem to do (we 
don't even pass in the dentry as an argument - you have to figure it out 
from the qstr, and a filesystem really should not do that!), but /proc 
_does_ look up the dentry in question, maybe some other insane filesystem 
does too and then does the __d_drop.

I'm not seeing it, though. So I still think the patch is sane and good, 
but somebody really needs to double- or triple-check me on it.

		Linus
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