# Re: \[PATCH v2 1/2\] HID: u2fzero: explicitly check for errors

- From: Andrej Shadura \<hidden\>
- Date: 2021-10-18 14:24:03 
- List: linux-input
- Page: https://ratatoskr.run/linux-input/2021/10/6886041
- Thread: https://ratatoskr.run/linux-input/2021/10/6886027/t.md

```text
On 18/10/2021 16:15, Alan Stern wrote:
> On Mon, Oct 18, 2021 at 02:21:43PM +0200, Andrej Shadura wrote:
>> The previous commit fixed handling of incomplete packets but broke error
>> handling: offsetof returns an unsigned value (size_t), but when compared
>> against the signed return value, the return value is interpreted as if
>> it were unsigned, so negative return values are never less than the
>> offset.
>>
>> Fixes: 22d65765f211 ("HID: u2fzero: ignore incomplete packets without data")
>> Fixes: 42337b9d4d95 ("HID: add driver for U2F Zero built-in LED and RNG")
>> Signed-off-by: Andrej Shadura <redacted>
>> ---
>>   drivers/hid/hid-u2fzero.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/hid/hid-u2fzero.c b/drivers/hid/hid-u2fzero.c
>> index d70cd3d7f583..5145d758bea0 100644
>> --- a/drivers/hid/hid-u2fzero.c
>> +++ b/drivers/hid/hid-u2fzero.c
>> @@ -200,7 +200,7 @@ static int u2fzero_rng_read(struct hwrng *rng, void *data,
>>   	ret = u2fzero_recv(dev, &req, &resp);
>>   
>>   	/* ignore errors or packets without data */
>> -	if (ret < offsetof(struct u2f_hid_msg, init.data))
>> +	if (ret < 0 || ret < offsetof(struct u2f_hid_msg, init.data))
>
> Although the patch description does a good job of explaining what's
> happening, someone merely reading the code will most likely not
> understand.
>
> One alternative is to add a comment.  Another is simply to force a
> signed integer comparison:
>
> 	if (ret < (ssize_t) offsetof(...

I have considered that, but I thought that is actually less readable than having two conditions. I’m curious that you say "ignore errors or packets without data" is not clear enough — how would you reword that without inflating it too much?

-- 
Cheers,
  Andrej
```