| From | Herton Ronaldo Krzesinski <> | Subject | [PATCH 29/74] staging: comedi: comedi_test: fix race when cancelling command | Date | Thu, 24 Jan 2013 01:26:41 -0200 |
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3.5.7.4 -stable review patch. If anyone has any objections, please let me know.
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From: Ian Abbott <abbotti@mev.co.uk>
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 <abbotti@mev.co.uk> Reported-by: Éric Piel <piel@delmic.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> [ herton: adjust context ] Signed-off-by: Herton Ronaldo Krzesinski <herton.krzesinski@canonical.com> --- drivers/staging/comedi/drivers/comedi_test.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/staging/comedi/drivers/comedi_test.c b/drivers/staging/comedi/drivers/comedi_test.c index 873e374..806c397 100644 --- a/drivers/staging/comedi/drivers/comedi_test.c +++ b/drivers/staging/comedi/drivers/comedi_test.c @@ -398,7 +398,7 @@ 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; } -- 1.7.9.5 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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