Re: [Qemu-devel] [PATCH for 2.5 1/2] net: pcnet: add check to validate receive data size(CVE-2015-7504)

[Jason Wang <jasowang@redhat.com>]

On 11/30/2015 06:46 PM, Michael S. Tsirkin wrote:
> On Mon, Nov 30, 2015 at 03:38:22PM +0800, Jason Wang wrote:
>> From: Prasad J Pandit <pjp@fedoraproject.org>
>>
>> In loopback mode, pcnet_receive routine appends CRC code to the
>> receive buffer. If the data size given is same as the buffer size,
>> the appended CRC code overwrites 4 bytes after s->buffer. Added a
>> check to avoid that.
>>
>> Reported by: Qinghao Tang <luodalongde@gmail.com>
>> Cc: qemu-stable@nongnu.org
>> Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
>> Signed-off-by: Jason Wang <jasowang@redhat.com>
> Reviewed-by: Michael S. Tsirkin <mst@redhat.com>

Applied to my -net. Thanks

>> ---
>>  hw/net/pcnet.c | 8 +++++---
>>  1 file changed, 5 insertions(+), 3 deletions(-)
>>
>> diff --git a/hw/net/pcnet.c b/hw/net/pcnet.c
>> index 0eb3cc4..309c40b 100644
>> --- a/hw/net/pcnet.c
>> +++ b/hw/net/pcnet.c
>> @@ -1084,7 +1084,7 @@ ssize_t pcnet_receive(NetClientState *nc, const uint8_t *buf, size_t size_)
>>                  uint32_t fcs = ~0;
>>                  uint8_t *p = src;
>>  
>> -                while (p != &src[size-4])
>> +                while (p != &src[size])
>>                      CRC(fcs, *p++);
>>                  crc_err = (*(uint32_t *)p != htonl(fcs));
>>              }
>> @@ -1233,8 +1233,10 @@ static void pcnet_transmit(PCNetState *s)
>>          bcnt = 4096 - GET_FIELD(tmd.length, TMDL, BCNT);
>>  
>>          /* if multi-tmd packet outsizes s->buffer then skip it silently.
>> -           Note: this is not what real hw does */
>> -        if (s->xmit_pos + bcnt > sizeof(s->buffer)) {
>> +         * Note: this is not what real hw does.
>> +         * Last four bytes of s->buffer are used to store CRC FCS code.
>> +         */
>> +        if (s->xmit_pos + bcnt > sizeof(s->buffer) - 4) {
>>              s->xmit_pos = -1;
>>              goto txdone;
>>          }
>> -- 
>> 2.5.0
>>