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

[Anthony Liguori <anthony@codemonkey.ws>]

On 07/12/2010 05:42 PM, Michael S. Tsirkin wrote:
> On Mon, Jul 12, 2010 at 04:07:21PM -0500, Anthony Liguori wrote:
>    
>> 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<mst@redhat.com>
>>>        
>> 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
>>      
> I am guessing there's no chance guest actually looks
> at this data, otherwise it won't match and we'd get errors, right?
>    

That's my assumption too.  Although I believe there are some known 
issues with e1000 and certain versions of Windows and the Microsoft 
built-in driver.  Maybe this is why those drivers don't work and the 
Intel drivers do?

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");
>>>