Re: [PATCH v2 3/8] bus: mhi: core: Read transfer length from an event properly

Hemant Kumar
2020-04-29T17:30:42Z

Hi Jeff

On 4/28/20 7:50 AM, Jeffrey Hugo wrote:
> On 4/27/2020 8:59 PM, Bhaumik Bhatt wrote:
>> From: Hemant Kumar <hemantk@codeaurora.org>
>>
>> When MHI Driver receives an EOT event, it reads xfer_len from the
>> event in the last TRE. The value is under control of the MHI device
>> and never validated by Host MHI driver. The value should never be
>> larger than the real size of the buffer but a malicious device can
>> set the value 0xFFFF as maximum. This causes device to memory
>
> The device will overflow, or the driver?
Done.
>
>> overflow (both read or write). Fix this issue by reading minimum of
>> transfer length from event and the buffer length provided.
>>
>> Signed-off-by: Hemant Kumar <hemantk@codeaurora.org>
>> Signed-off-by: Bhaumik Bhatt <bbhatt@codeaurora.org>
>> ---
>>   drivers/bus/mhi/core/main.c | 5 ++++-
>>   1 file changed, 4 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/bus/mhi/core/main.c b/drivers/bus/mhi/core/main.c
>> index 1ccd4cc..3d468d9 100644
>> --- a/drivers/bus/mhi/core/main.c
>> +++ b/drivers/bus/mhi/core/main.c
>> @@ -521,7 +521,10 @@ static int parse_xfer_event(struct mhi_controller
>> *mhi_cntrl,
>>                   mhi_cntrl->unmap_single(mhi_cntrl, buf_info);
>>               result.buf_addr = buf_info->cb_buf;
>> -            result.bytes_xferd = xfer_len;
>> +
>> +            /* truncate to buf len if xfer_len is larger */
>> +            result.bytes_xferd =
>> +                min_t(u16, xfer_len, buf_info->len);
>>               mhi_del_ring_element(mhi_cntrl, buf_ring);
>>               mhi_del_ring_element(mhi_cntrl, tre_ring);
>>               local_rp = tre_ring->rp;
>>
>
>