Re: [PATCH v2] usb: devio: Add ioctl to disallow detaching kernel USB drivers.

From: Emilio LÃpez
Date: Sun Jan 24 2016 - 21:06:15 EST

Hi BjÃrn,

El 22/01/16 a las 06:41, BjÃrn Mork escribiÃ:
Emilio LÃpez <emilio.lopez@xxxxxxxxxxxxxxx> 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

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!