Re: [PATCH] net: ax88179: add proper error handling of usb read errors

[Oliver Neukum]

On 14.04.22 10:21, Dan Carpenter wrote:
> On Thu, Apr 14, 2022 at 09:31:56AM +0200, Oliver Neukum wrote:
>>
>> On 13.04.22 17:32, Dan Carpenter wrote:
>>> Bug: buffer partially filled.  Information leak.
>>>
>>> If you return the bytes then the only correct way to write error
>>> handling is:
>>>
>>> 	if (ret < 0)
>>> 		return ret;
>>> 	if (ret != size)
>>> 		return -EIO;
>>>
>> You have to make up your mind on whether you ever need to read
>> answer of a length not known before you try it. The alternative of
>> passing a pointer to an integer for length is worse.
> How is it worse?  Can you give an example, so I will write a static
> checker rule for it?
My favorite example would be:

int usb_bulk_msg(struct usb_device *usb_dev, unsigned int pipe,
                void *data, int len, int *actual_length, int timeout)

The actual_length parameter is horrible. Now, there are situations like this
where this pattern is unavoidable, because in addition to an error you
can get a partial completion of an operation.

Do I see it correctly that you would prefer this pattern even if
you could report either an error or a result in the function?
> There used to be more APIs that consistently caused bug after bug where
> we mixed positives success values with negative error codes.  We
> converted some bad offenders to return the positive as a parameter
> and I was really happy about that.
>
> Another example I used to see a lot is request_irq() saved to an
> unsigned.  These days I think GCC warns about that?  Maybe the build
> bots get to it before I do.
>
That needs to be checked for.. In fact while we are at it, do we check
for integer overflows?

    Regards
        Oliver