linux-kernel - Re: Chroot bug

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Message-ID: <46F93EAF.20706@prepere.com>
Date:	Tue, 25 Sep 2007 19:00:31 +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,
	linux-kernel@...r.kernel.org
Subject: Re: Chroot bug


>> This  does not help.  Let's try:
>> chroot somewhere
>> mkdir foo
>> fd = open /
>> chroot foo
>>     
>
> ('fd' implicitly closed and chdir to /foo)
>   
Really? Try it. I am sure, that this works. You can create directory in 
chroot and break chroot by this. fd is not closed, because linux doesn't 
close descriptors by chroot syscall. this can be done every time if you 
have CAP_SYS_CHROOT.
>   
>> fchdir fd
>>     
>
> -EINVAL
>
>   
>> chdir ".."
>>     
>
> /../ => /
>
>   
>> ....
>> chdir ".."
>> chroot "."
>> so you are in root.
>>     
>
> so we remain in chroot.
>   

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