Re: [Qemu-devel] [PATCH v4 04/30] virtio-net: fix buffer overflow on invalid state load

["Michael S. Tsirkin" <mst@redhat.com>]

On Mon, Mar 31, 2014 at 07:21:30PM +0200, Laszlo Ersek wrote:
> On 03/31/14 16:16, Michael S. Tsirkin wrote:
> > CVE-2013-4148 QEMU 1.0 integer conversion in
> > virtio_net_load()@hw/net/virtio-net.c
> > 
> > Deals with loading a corrupted savevm image.
> > 
> >>         n->mac_table.in_use = qemu_get_be32(f);
> > 
> > in_use is int so it can get negative when assigned 32bit unsigned value.
> > 
> >>         /* MAC_TABLE_ENTRIES may be different from the saved image */
> >>         if (n->mac_table.in_use <= MAC_TABLE_ENTRIES) {
> > 
> > passing this check ^^^
> > 
> >>             qemu_get_buffer(f, n->mac_table.macs,
> >>                             n->mac_table.in_use * ETH_ALEN);
> > 
> > with good in_use value, "n->mac_table.in_use * ETH_ALEN" can get
> > positive and bigger than mac_table.macs. For example 0x81000000
> > satisfies this condition when ETH_ALEN is 6.
> > 
> > A similar problem exists with is_multi.
> 
> ("first_multi")

Actually it doesn't even exist: Peter commented on this in v1
and I forgot to fix up the commit log :(
I really wanted to fix the commit log to say
"make first_multi unsigned for consistency" but
forgot.

> > 
> > Fix both by making the value unsigned.
> > 
> > Reviewed-by: Michael Roth <mdroth@linux.vnet.ibm.com>
> > Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> > Edit: "for consistency, change first_multi as well".
> > 
> > Note: all call sites were audited to confirm that
> > making them unsigned didn't cause any issues:
> > it turns out we actually never do math on them,
> > so it's easy to validate because both values are
> > always <= MAC_TABLE_ENTRIES.
> > ---
> >  include/hw/virtio/virtio-net.h | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/include/hw/virtio/virtio-net.h b/include/hw/virtio/virtio-net.h
> > index df60f16..4b32440 100644
> > --- a/include/hw/virtio/virtio-net.h
> > +++ b/include/hw/virtio/virtio-net.h
> > @@ -176,8 +176,8 @@ typedef struct VirtIONet {
> >      uint8_t nobcast;
> >      uint8_t vhost_started;
> >      struct {
> > -        int in_use;
> > -        int first_multi;
> > +        uint32_t in_use;
> > +        uint32_t first_multi;
> >          uint8_t multi_overflow;
> >          uint8_t uni_overflow;
> >          uint8_t *macs;
> > 
> 
> I ran
> 
>   git grep -EHn '\<(in_use|first_multi)\>'
> 
> Many hits, hard to audit (esp. because I'm unfamiliar with the code).
> Several loops with signed int loop variables. I checked cursorily.
> 
> Reviewed-by: Laszlo Ersek <lersek@redhat.com>
>