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SubjectPossible null pointer dereference in rcar-dmac.ko
Date
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@ispras.ru

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