commit 9590232bb4 upstream.
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.
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: Ben Hutchings <ben@decadent.org.uk>
ce626e14b2