Re: [Qemu-devel] [PATCH 12/23] stellaris_enet: avoid buffer orerrun on incoming migration (part 3)

[Peter Maydell]

On 3 December 2013 16:28, Michael S. Tsirkin <address@hidden> wrote:
> From: Michael Roth <address@hidden>
>
> CVE-2013-4532
>
> s->tx_frame_len is read from the wire and can later used as an index
> into s->tx_fifo[] for memset() when a DATA command is issued by the guest.
>
> In this case s->tx_frame_len is checked to avoid an overrun, but if the
> value is negative a subsequently executed guest can underrun the buffer
> with zeros via the memset() call.
>
> Fix this by failing migration if the incoming value is of s->tx_frame_len
> is less than -1 (the emulation code allows from -1 as a special case)
>
> Signed-off-by: Michael Roth <address@hidden>
> Signed-off-by: Michael S. Tsirkin <address@hidden>
> ---
>  hw/net/stellaris_enet.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/hw/net/stellaris_enet.c b/hw/net/stellaris_enet.c
> index 65f0ba8..6eca31e 100644
> --- a/hw/net/stellaris_enet.c
> +++ b/hw/net/stellaris_enet.c
> @@ -375,6 +375,9 @@ static int stellaris_enet_load(QEMUFile *f, void *opaque, 
> int version_id)
>      s->mrxd = qemu_get_be32(f);
>      s->np = qemu_get_be32(f);
>      s->tx_frame_len = qemu_get_be32(f);
> +    if (s->tx_frame_len < -1) {
> +        return -EINVAL;
> +    }

Don't we need to also check that tx_frame_len <= 2032?

Otherwise the migration stream could set it to some large
positive number and use this to bypass the check on whether
writing to tx_fifo[tx_fifo_len] has hit the end of the fifo buffer,
I think.

>      s->tx_fifo_len = qemu_get_be32(f);
>      if (s->tx_fifo_len < 0 || s->tx_fifo_len > SE_FIFO_LEN) {
>          return -EINVAL;
> --
> MST
>

thanks
-- PMM