Re: [Qemu-arm] [Qemu-devel] [PATCH] cadence_gem: fix buffer overflow

[Peter Crosthwaite]

On Mon, Jan 18, 2016 at 12:12 AM, Jason Wang <address@hidden> wrote:
>
>
> On 01/18/2016 03:04 PM, Peter Crosthwaite wrote:
>> On Sun, Jan 17, 2016 at 10:50 PM, Jason Wang <address@hidden> wrote:
>>>
>>> On 01/14/2016 05:43 PM, Michael S. Tsirkin wrote:
>>>> gem_receive copies a packet received from network into an rxbuf[2048]
>>>> array on stack, with size limited by descriptor length set by guest.  If
>>>> guest is malicious and specifies a descriptor length that is too large,
>>>> and should packet size exceed array size, this results in a buffer
>>>> overflow.
>>>>
>>>> Reported-by: 刘令 <address@hidden>
>>>> Signed-off-by: Michael S. Tsirkin <address@hidden>
>>>> ---
>>>>  hw/net/cadence_gem.c | 8 ++++++++
>>>>  1 file changed, 8 insertions(+)
>>> Apply to my -net with tweak on commit log (changing receive to transmit
>>> as noticed).
>>>
>> As this is actually an unimplemented feature you should change the
>> message to a LOG_UNIMP rather than a debug printf.
>>
>> Regards,
>> Peter
>
> Thanks for the reminding. But we need know the whether real device could
> send packet whose length is greater than 2048. Do you know the link to
> the manual? (Haven't fond it in cadence page.) A hint is the linux

Xilinx UG585 has details:

http://www.xilinx.com/support/documentation/user_guides/ug585-Zynq-7000-TRM.pdf

Regards,
Peter

> driver (drivers/net/ethernet/cadence/macb.c), use 1500 as its MTU.
>
>>
>>> Thanks
>>>
>>>> diff --git a/hw/net/cadence_gem.c b/hw/net/cadence_gem.c
>>>> index 3639fc1..15a0786 100644
>>>> --- a/hw/net/cadence_gem.c
>>>> +++ b/hw/net/cadence_gem.c
>>>> @@ -862,6 +862,14 @@ static void gem_transmit(CadenceGEMState *s)
>>>>              break;
>>>>          }
>>>>
>>>> +        if (tx_desc_get_length(desc) > sizeof(tx_packet) - (p - 
>>>> tx_packet)) {
>>>> +            DB_PRINT("TX descriptor @ 0x%x too large: size 0x%x space 
>>>> 0x%x\n",
>>>> +                     (unsigned)packet_desc_addr,
>>>> +                     (unsigned)tx_desc_get_length(desc),
>>>> +                     sizeof(tx_packet) - (p - tx_packet));
>>>> +            break;
>>>> +        }
>>>> +
>>>>          /* Gather this fragment of the packet from "dma memory" to our 
>>>> contig.
>>>>           * buffer.
>>>>           */
>