From patchwork Thu Jan 24 03:26:41 2013 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Subject: [29/74] staging: comedi: comedi_test: fix race when cancelling command From: Herton Ronaldo Krzesinski X-Patchwork-Id: 215142 Message-Id: <1358998046-613-30-git-send-email-herton.krzesinski@canonical.com> To: linux-kernel@vger.kernel.org, stable@vger.kernel.org, kernel-team@lists.ubuntu.com Cc: Greg Kroah-Hartman , Ian Abbott Date: Thu, 24 Jan 2013 01:26:41 -0200 3.5.7.4 -stable review patch. If anyone has any objections, please let me know. ------------------ From: Ian Abbott 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 [ herton: adjust context ] Signed-off-by: Herton Ronaldo Krzesinski --- 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; }