Re: Chroot bug

[Jan Engelhardt]

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."
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