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

["Venkateswararao Jujjuri (JV)" <jvrao@linux.vnet.ibm.com>]

On 3/10/2011 4:29 AM, Stefan Hajnoczi wrote:
> On Wed, Mar 9, 2011 at 5:16 PM, M. Mohan Kumar <mohan@in.ibm.com> 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.

Thanks,
JV

> I'm not 100% sure of the semantics but I suspect that chmodat(dir_fd,
> "..", ...) does not honor the chroot since your current task is not
> inside the chroot.  If so, then you can manipulate the parent
> directory of the chroot using some of the operations added in this
> patch.
> 
> The safe solution is to perform all operations inside the chroot.
> This will require extending the chroot socket protocol.
> 
> Stefan
>