From: Ian Abbott Date: Fri, 4 Jan 2013 11:33:21 +0000 (+0000) Subject: staging: comedi: comedi_test: fix race when cancelling command X-Git-Tag: firefly_0821_release~7541^2~122 X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=2d8a66efb832e17e906415a4e563182258cc0ab2;p=firefly-linux-kernel-4.4.55.git staging: comedi: comedi_test: fix race when cancelling command commit c0729eeefdcd76db338f635162bf0739fd2c5f6f upstream. Éric Piel reported a kernel oops in the "comedi_test" module. It was a NULL pointer dereference within `waveform_ai_interrupt()` (actually a timer function) that sometimes occurred when a running asynchronous command is cancelled (either by the `COMEDI_CANCEL` ioctl or by closing the device file). This seems to be a race between the caller of `waveform_ai_cancel()` which on return from that function goes and tears down the running command, and the timer function which uses the command. In particular, `async->cmd.chanlist` gets freed (and the pointer set to NULL) by `do_become_nonbusy()` in "comedi_fops.c" but a previously scheduled `waveform_ai_interrupt()` timer function will dereference that pointer regardless, leading to the oops. Fix it by replacing the `del_timer()` call in `waveform_ai_cancel()` with `del_timer_sync()`. Signed-off-by: Ian Abbott Reported-by: Éric Piel Signed-off-by: Greg Kroah-Hartman --- diff --git a/drivers/staging/comedi/drivers/comedi_test.c b/drivers/staging/comedi/drivers/comedi_test.c index a804742b8022..2567f9ab4167 100644 --- a/drivers/staging/comedi/drivers/comedi_test.c +++ b/drivers/staging/comedi/drivers/comedi_test.c @@ -461,7 +461,7 @@ static int waveform_ai_cancel(struct comedi_device *dev, struct comedi_subdevice *s) { devpriv->timer_running = 0; - del_timer(&devpriv->timer); + del_timer_sync(&devpriv->timer); return 0; }