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Re: [Qemu-devel] Re: [V8 PATCH 11/11] virtio-9p: Chroot environment for

From: Stefan Hajnoczi
Subject: Re: [Qemu-devel] Re: [V8 PATCH 11/11] virtio-9p: Chroot environment for other functions
Date: Fri, 11 Mar 2011 06:30:46 +0000

On Fri, Mar 11, 2011 at 5:54 AM, Venkateswararao Jujjuri (JV)
<address@hidden> wrote:
> On 3/10/2011 4:29 AM, Stefan Hajnoczi wrote:
>> On Wed, Mar 9, 2011 at 5:16 PM, M. Mohan Kumar <address@hidden> wrote:
>>> Add chroot functionality for systemcalls that can operate on a file
>>> using relative directory file descriptor.
>> I suspect the relative directory approach is broken and escapes the
>> chroot.  Here's why:
>> The request is local_chmod(fs_ctx, "/..", credp).  dirname("/..") is
>> "/" and basename("..") is "..".
> We should never receive protocol operations with relative path.
> Client should always resolve to full path and send the request.
> If the client is malicious this scenario can be be possible.. but in that case
> it is fine to fail the operation.

What I haven't audited yet is whether symlinks can be abused in any of
these *at(2) operations.

The *at(2) approach seems like a shortcut to avoid implementing
individual chroot protocol requests/responses for stat(2) and friends.
 But it carries the risk that if we don't use NOFOLLOW then we can be
tricked into escaping the "chroot" because we're performing the
operation outside the chroot.

I'll take a look later today to make sure all operations safe traverse
paths outside the chroot.


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