Possible null pointer dereference in rcar-dmac.ko

[Anton Volkov]

Hello.

While searching for races in the Linux kernel I've come across 
"drivers/dma/sh/rcar-dmac.ko" module. Here is a question that I came up 
with while analyzing results. Lines are given using the info from Linux 
v4.12.

Consider the following case:

Thread 1:                            Thread 2:
rcar_dmac_probe
->rcar_dmac_chan_probe
             (&dmac->channels[i])
    rchan = &dmac->channels[i]
    chan = &rchan->chan
    devm_request_threaded_irq(rchan)
    chan->device = &dmac->engine    rcar_dmac_isr_channel
                                    ->rcar_dmac_isr_transfer_end(chan)
                                      ->rcar_dmac_chan_start_xfer(chan)
  engine->dev = &pdev->dev;               <READ chan->chan.device->dev>
  (rcar-dmac.c: line 1828)                (rcar-dmac.c: line 351)

As far as I understand engine->dev is NULL before its initialization in 
probe. Thus there might be a NULL pointer dereference in 
rcar_dmac_chan_start_xfer while accessing chan->chan.device->dev which 
is equal to (&dmac->engine)->dev. Is this possible from your point of view?

Thank you for your time.

-- Anton Volkov
Linux Verification Center, ISPRAS
web: http://linuxtesting.org
e-mail: avolkov@xxxxxxxxx