linux-kernel - Re: Chroot bug

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Message-ID: <46F940B9.8060006@prepere.com>
Date:	Tue, 25 Sep 2007 19:09:13 +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

Jan Engelhardt napsal(a):
> On Sep 25 2007 19:00, Miloslav Semler wrote:
>   
>>>> 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.
>>     
>
> In case you have not followed my earlier email, I'll repost:
>
> |>> So what? Just do this: chdir into the root after chroot.
> |>
> |> I don't think so.  His exploit just got me all the way out of a 
> |> chroot within a chroot within a chroot, inclusive of lots of 
> |> chdirs.
> |>
> |
> |Close all fds that point to directories outside the root ;-)
>
> Perhaps that was formulated a bit sloppy. It of course means
> "On chroot(2), implicitly close all FDs that point outside."
>   
yes, but I can use fds from chroot ;-) ....
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