Re: [PATCH]mini-os: Bug in allocate_xenbus_id()

[Grzegorz Milos <gm281@cam.ac.uk>]

That's a good catch. Did you see the bug manifesting itself in practice?

Keir could you apply please?
Thanks.
Gregor

Dietmar Hahn wrote:
> Hi Gregor,
> 
> in allocate_xenbus_id() the static variable probe never gets reset.
> Therewidth id's >= NR_REQS are possible, which lead to an overflow in
> req_info[] and may crash the  mini-os.
> Thanks.
> 
> Dietmar
> 
> Signed-off-by: Dietmar Hahn <dietmar.hahn@fujitsu-siemens.com>
> 
> # HG changeset patch
> # User dietmar.hahn@fujitsu-siemens.com
> # Date 1171877953 -3600
> # Node ID 3d04558ad3d7e3811ac8c827bb876858bbb1c415
> # Parent  b5fc88aad1b0eb35d12e503982c70fdc27f0544a
> Because probe never gets decremented (or reset), id >= NR_REQS is possible, 
> which may lead to a crash.
> 
> diff -r b5fc88aad1b0 -r 3d04558ad3d7 extras/mini-os/xenbus/xenbus.c
> --- a/extras/mini-os/xenbus/xenbus.c    Sun Feb 18 15:29:40 2007 +0000
> +++ b/extras/mini-os/xenbus/xenbus.c    Mon Feb 19 10:39:13 2007 +0100
> @@ -210,7 +210,7 @@ static int allocate_xenbus_id(void)
>      }
>      nr_live_reqs++;
>      req_info[o_probe].in_use = 1;
> -    probe = o_probe + 1;
> +    probe = (o_probe + 1) % NR_REQS;
>      spin_unlock(&req_lock);
>      init_waitqueue_head(&req_info[o_probe].waitq);