[Qemu-devel] Re: [PATCH RFC] e1000: fix access 4 bytes beyond buffer end

[Anthony Liguori]

On 07/12/2010 12:48 PM, Michael S. Tsirkin wrote:
> We do range check for size, and get size as buffer,
> but copy size + 4 bytes (4 is for FCS).
> Let's copy size bytes but put size + 4 in length.
>
> Signed-off-by: Michael S. Tsirkin<address@hidden>
>    

I think I'd feel slightly better if we zero'd out the FCS before writing 
it to the guest.  It is potentially a data leak.

Regards,

Anthony Liguori

> ---
>
> Anthony, Alex, please review.
>
>   hw/e1000.c |    3 +--
>   1 files changed, 1 insertions(+), 2 deletions(-)
>
> diff --git a/hw/e1000.c b/hw/e1000.c
> index 0da65f9..70aba11 100644
> --- a/hw/e1000.c
> +++ b/hw/e1000.c
> @@ -649,7 +649,6 @@ e1000_receive(VLANClientState *nc, const uint8_t *buf, 
> size_t size)
>       }
>
>       rdh_start = s->mac_reg[RDH];
> -    size += 4; // for the header
>       do {
>           if (s->mac_reg[RDH] == s->mac_reg[RDT]&&  s->check_rxov) {
>               set_ics(s, 0, E1000_ICS_RXO);
> @@ -663,7 +662,7 @@ e1000_receive(VLANClientState *nc, const uint8_t *buf, 
> size_t size)
>           if (desc.buffer_addr) {
>               cpu_physical_memory_write(le64_to_cpu(desc.buffer_addr),
>                                         (void *)(buf + vlan_offset), size);
> -            desc.length = cpu_to_le16(size);
> +            desc.length = cpu_to_le16(size + 4 /* for FCS */);
>               desc.status |= E1000_RXD_STAT_EOP|E1000_RXD_STAT_IXSM;
>           } else // as per intel docs; skip descriptors with null buf addr
>               DBGOUT(RX, "Null RX descriptor!!\n");
>