[v2,0/3] URB_FREE_COHERENT gs_usb memory leak fix

Message

Rhett Aultman June 9, 2022, 8:47 p.m. UTC

This patchset is a v2 replacement for an earlier patch to resolve a
memory leak which can occur with successive iterations of calling
gs_can_open() and gs_can_close().  The central cause of this memory
leak, which is an issue common to many of the USB CAN drivers, is that
memory allocated for RX buffers using usb_alloc_coherent() and then kept
in the URB will be properly freed when the URB is killed.  This
assumption is incorrect, as memory allocated with usb_alloc_coherent()
must be freed with usb_free_coherent(), and there is no provision for this
in the existing URB code.

The common solution to this, found in v1 of my patches as well as in
already merged patches for other CAN USB drivers (see the patch for the
esd CAN-USB/2 driver here:
https://www.spinics.net/lists/linux-can/msg08203.html) is for the driver
itself to maintain an array of addresses of the buffers allocated with
usb_alloc_coherent() and to then iteratively call usb_free_coherent() on
them in their close function.  This solution requires a driver developer
to understand this unclear nuance, and it has historically been solved
in a piecemeal way one driver at a time (note: the gs_usb driver has had
this issue since the 3.x.x kernel series).

Rather than continue to place the burden of complexity on the drivers,
this patchset adds a new URB flag which allows the DMA buffer to be
correctly freed with the URB is killed.  This results in a much simpler
solution at the driver level and with minimal additional code in the USB
core.

Rhett Aultman (3):
  drivers: usb/core/urb: Add URB_FREE_COHERENT
  drivers: usb/core/urb: allow URB_FREE_COHERENT
  can: gs_usb: fix DMA memory leak on close

 drivers/net/can/usb/gs_usb.c | 2 +-
 drivers/usb/core/urb.c       | 5 ++++-
 include/linux/usb.h          | 3 ++-
 3 files changed, 7 insertions(+), 3 deletions(-)