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SubjectRe: [PATCH v2] usb: devio: Add ioctl to disallow detaching kernel USB drivers.
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Hi Bjørn,

El 22/01/16 a las 06:41, Bjørn Mork escribió:
> Emilio López <emilio.lopez@collabora.co.uk> writes:
>
>> diff --git a/drivers/usb/core/devio.c b/drivers/usb/core/devio.c
>> index 38ae877c..bf40aa6 100644
>> --- a/drivers/usb/core/devio.c
>> +++ b/drivers/usb/core/devio.c
>> @@ -77,6 +77,8 @@ struct usb_dev_state {
>> unsigned long ifclaimed;
>> u32 secid;
>> u32 disabled_bulk_eps;
>> + bool privileges_dropped;
>> + unsigned long interface_allowed_mask;
>> };
>>
>> struct async {
>> @@ -641,6 +643,14 @@ static int claimintf(struct usb_dev_state *ps, unsigned int ifnum)
>> if (test_bit(ifnum, &ps->ifclaimed))
>> return 0;
>>
>> + if (ps->privileges_dropped) {
>> + if (ifnum >= 8*sizeof(ps->interface_allowed_mask))
>> + return -EINVAL;
>
>
> I don't think you need this runtime test. You can just make sure that
> sizeof(ps->interface_allowed_mask) == sizeof(ps->ifclaimed) at build
> time.
>
> I do find this variable and arbitrary limit a bit confusing, but that's
> not your fault - I guess it is an indication that ifnums > 31 are rare
> :)
>
>
>> diff --git a/include/uapi/linux/usbdevice_fs.h b/include/uapi/linux/usbdevice_fs.h
>> index 019ba1e..9abcb34 100644
>> --- a/include/uapi/linux/usbdevice_fs.h
>> +++ b/include/uapi/linux/usbdevice_fs.h
>> @@ -154,6 +154,10 @@ struct usbdevfs_streams {
>> unsigned char eps[0];
>> };
>>
>> +struct usbdevfs_drop_privs {
>> + unsigned long interface_allowed_mask;
>> +};
>> +
>
> "unsigned long" isn't a very good choice here, is it?

I went with a type matching ifclaimed on struct usb_dev_state to keep
the limit the same, but I guess it's not the best idea for an ioctl. I
can switch it to __u32, keeping the runtime check above as is, or use
__u64. Which one would you prefer?

Thanks for the review!
Emilio

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