linux-kernel - Re: [PATCH] nextfd(2)

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Message-ID: <782e192e-e1b5-4c53-895d-1eac4a4c9097@email.android.com>
Date:	Sun, 01 Apr 2012 18:37:26 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Kyle Moffett <kyle@...fetthome.net>
CC:	Alexey Dobriyan <adobriyan@...il.com>, akpm@...ux-foundation.org,
	viro@...iv.linux.org.uk, torvalds@...ux-foundation.org,
	drepper@...il.com, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH] nextfd(2)

Are those use cases heavyweight enough to motivate a new interface?

Kyle Moffett <kyle@...fetthome.net> wrote:

>On Sun, Apr 1, 2012 at 15:03, H. Peter Anvin <hpa@...or.com> wrote:
>> On 04/01/2012 05:57 AM, Alexey Dobriyan wrote:
>>> * /proc/self/fd is unreliable:
>>>   proc may be unconfigured or not mounted at expected place.
>>>   Looking at /proc/self/fd requires opening directory
>>>   which may not be available due to malicious rlimit drop or ENOMEM
>situations.
>>>   Not opening directory is equivalent to dumb close(2) loop except
>slower.
>>
>> This is really the motivation for this... the real question is how
>much
>> functionality is actually available in the system without /proc
>mounted,
>> and in particular if this particular subcase is worth optimizing ...
>> after all, if someone is maliciously setting rlimit, we can just
>abort
>> (if someone can set an rlimit they can also force an abort) or revert
>to
>> the slow path.
>
>Well, I imagine one typical usecase for closing all FDs is for
>security isolation purposes (EG: chroot()+etc), and in a great deal of
>chroot environments you don't have /proc available.  In particular
>/proc has been a source of a lot of privilege escalations in the past,
>so avoiding mounting it in a chroot is good security policy if
>possible.
>
>Cheers,
>Kyle Moffett

-- 
Sent from my mobile phone. Please excuse my brevity and lack of formatting.
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