media: mtk-jpeg: fix use-after-free in release path due to uncancelled work

In the Linux kernel, the following vulnerability has been resolved:

media: mtk-jpeg: fix use-after-free in release path due to uncancelled work

The mtk_jpeg_release() function frees the context structure (ctx) without

first cancelling any pending or running work in ctx->jpeg_work. This

creates a race window where the workqueue callback may still be accessing

the context memory after it has been freed.

Race condition:

CPU 0 (release) CPU 1 (workqueue)

---------------- ------------------

close()

mtk_jpeg_release()

mtk_jpegenc_worker()

ctx = work->data

// accessing ctx

kfree(ctx) // freed!

access ctx // UAF!

The work is queued via queue_work() during JPEG encode/decode operations

(via mtk_jpeg_device_run). If the device is closed while work is pending

or running, the work handler will access freed memory.

Fix this by calling cancel_work_sync() BEFORE acquiring the mutex. This

ordering is critical: if cancel_work_sync() is called after mutex_lock(),

and the work handler also tries to acquire the same mutex, it would cause

a deadlock.

Note: The open error path does NOT need cancel_work_sync() because

INIT_WORK() only initializes the work structure - it does not schedule

it. Work is only scheduled later during ioctl operations.