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EunTaik Lee authored
[ Upstream commit 9590232b ] 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:
Sasha Levin <alexander.levin@verizon.com>
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