[0/6] USB: gadget: f_hid: fix lifetime issues

Message

John Keeping Oct. 24, 2019, 4:45 p.m. UTC

File descriptors referencing the /dev/hidgN device created by the HID
gadget can outlive the underlying gadget function, which creates easy to
trigger use-after-frees in the kernel.

A simple reproduction for this using the libusbgx example programs is:

	$ gadget-hid
	$ exec 3<> /dev/hidg0
	$ gadget-vid-pid-remove
	$ exec 3<&-

Closing the file descriptor on the last line triggers a use-after-free
which can be seen immediately with slub_debug=P.

This series fixes this by making the struct cdev associated with the
module rather than dynamically allocated for the gadget and changing
struct f_hidg to be refcounted instead of tied to the gadget lifetime.

John Keeping (6):
  USB: gadget: f_hid: move chardev setup to module init
  USB: gadget: f_hid: switch to IDR for tracking minors
  USB: gadget: f_hid: find f_hidg by IDR lookup on open
  USB: gadget: f_hid: decouple cdev from f_hidg lifetime
  USB: gadget: f_hid: refcount f_hidg structure
  USB: gadget: f_hid: return ENODEV from read/write after deletion

 drivers/usb/gadget/function/f_hid.c | 141 +++++++++++++++++++---------
 drivers/usb/gadget/function/u_hid.h |   3 -
 2 files changed, 95 insertions(+), 49 deletions(-)