linux-kernel - Re: Chroot bug

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Date:	Tue, 25 Sep 2007 17:39:19 +0200
From:	Miloslav Semler <majkls@...pere.com>
To:	Jan Engelhardt <jengelh@...putergmbh.de>
CC:	serge@...lyn.com, davidsen@....com, philipp@...ek.priv.at,
	7eggert@....de, alan@...rguk.ukuu.org.uk, bunk@...tum.de,
	linux-kernel@...r.kernel.org
Subject: Re: Chroot bug


> On Sep 26 2007 00:40, David Newall wrote:
>   
>> Miloslav Semler pointed out that a root process can chdir("..") out of its
>> chroot.  Although this is documented in the man page, it conflicts with the
>> essential function, which is to change the root directory of the process.  In
>> addition to any creative uses, for example Philipp Marek's loading dynamic
>> libraries, it seems clear that the prime purpose of chroot is to aid security.
>> Being able to cd your way out is handy for the bad guys, but the good guys
>> don't need it; there are a thousand better, safer solutions.
>>     
>
> So what? Just do this: chdir into the root after chroot.
>
> It won't conform to SVR4/4.4BSD anymore, but hey, let Linux set some
> sane standard ain't bad either. I doubt anyone really relies on the
> fact that after chroot, your cwd might be outside the root.
>   
so then you corrupt pwd. I think that working directory should be set 
only if it is necessary. Fn directory_is_out is not big performace loss. 
And also you can break this fix with fchdir.

Miloslav
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