staging/android/ion : fix a race condition in the ion driver
authorEunTaik Lee <eun.taik.lee@samsung.com>
Wed, 24 Feb 2016 04:38:06 +0000 (04:38 +0000)
committermobile promotions <svcmobile_promotions@nvidia.com>
Thu, 1 Dec 2016 09:04:03 +0000 (01:04 -0800)
commit1b9f44b69ea5b06977fc061622008d300834ca63
tree6a08bdbaf84d1e1b3159a32619d24cbf287eff9e
parentbcc1956d41e4f11e8100600bb9bb77930b21fd9c
staging/android/ion : fix a race condition in the ion driver

There is a use-after-free problem in the ion driver.
This is caused by a race condition in the ion_ioctl()
function.

A handle has ref count of 1 and two tasks on different
cpus calls ION_IOC_FREE simultaneously.

cpu 0                                   cpu 1
-------------------------------------------------------
ion_handle_get_by_id()
(ref == 2)
                            ion_handle_get_by_id()
                            (ref == 3)

ion_free()
(ref == 2)

ion_handle_put()
(ref == 1)

                            ion_free()
                            (ref == 0 so ion_handle_destroy() is
                            called
                            and the handle is freed.)

                            ion_handle_put() is called and it
                            decreases the slub's next free pointer

The problem is detected as an unaligned access in the
spin lock functions since it uses load exclusive
 instruction. In some cases it corrupts the slub's
free pointer which causes a mis-aligned access to the
next free pointer.(kmalloc returns a pointer like
ffffc0745b4580aa). And it causes lots of other
hard-to-debug problems.

This symptom is caused since the first member in the
ion_handle structure is the reference count and the
ion driver decrements the reference after it has been
freed.

To fix this problem client->lock mutex is extended
to protect all the codes that uses the handle.

Bug 1836932

Change-Id: I45abd9dd1f696105a7840a25ba4a594b5af4fa65
Signed-off-by: Eun Taik Lee <eun.taik.lee@samsung.com>
Reviewed-by: Laura Abbott <labbott@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Gagan Grover <ggrover@nvidia.com>
Reviewed-on: http://git-master/r/1262250
Reviewed-by: Dhiren Parmar <dparmar@nvidia.com>
drivers/staging/android/ion/ion.c [changed mode: 0644->0755]