Re: [PATCH-for-6.1] hw/net/can: sja1000 fix buff2frame_bas for dlc out of std CAN 8 bytes

[Philippe Mathieu-Daudé]

Cc'ing QEMU fuzz team.

On 7/29/21 11:19 AM, Pavel Pisa wrote:
> Hello everybody,
> 
> please, can somebody accept the fix for master?
> It should be ideally applied even to stable
> branches.
> 
> Or should I send request through some other form
> then on the list?

I suppose the patch fell through the cracks.

Apparently Paolo doesn't like to queue fuzzer fixes without
reproducer. For examples see tests/qtest/fuzz-*.c in the tree.

> 
> Thanks,
> 
> Pavel
> 
> On Monday 26 of July 2021 18:24:58 Pavel Pisa wrote:
>> Problem reported by openEuler fuzz-sig group.
>>
>> The buff2frame_bas function (hw\net\can\can_sja1000.c)
>> infoleak(qemu5.x~qemu6.x) or stack-overflow(qemu 4.x).
>>

If you want the patch backported in stable releases, please
include:

Cc: qemu-stable@nongnu.org

>> Reported-by: Qiang Ning <ningqiang1@huawei.com>
>> Signed-off-by: Pavel Pisa <pisa@cmp.felk.cvut.cz>
>> ---
>>  hw/net/can/can_sja1000.c | 4 ++++
>>  1 file changed, 4 insertions(+)
>>
>> diff --git a/hw/net/can/can_sja1000.c b/hw/net/can/can_sja1000.c
>> index 42d2f99dfb..64e81bff58 100644
>> --- a/hw/net/can/can_sja1000.c
>> +++ b/hw/net/can/can_sja1000.c
>> @@ -311,6 +311,10 @@ static void buff2frame_bas(const uint8_t *buff,
>> qemu_can_frame *frame) }
>>      frame->can_dlc = buff[1] & 0x0f;
>>
>> +    if (frame->can_dlc > 8) {
>> +        frame->can_dlc = 8;
>> +    }
>> +

This doesn't seem a complete fix (see buff2frame_pel).

Here can_dlc shouldn't be more than 8.

What you can do here (and in buff2frame_pel) is:

        assert(frame->can_dlc <= 8);

and find where the field is abused, probably discarding
invalid frames earlier?

>>      for (i = 0; i < frame->can_dlc; i++) {
>>          frame->data[i] = buff[2 + i];
>>      }