Messages in this thread Patch in this message | | | Date | Tue, 04 Jun 2013 19:22:39 +0200 | From | Willy Tarreau <> | Subject | [ 069/184] staging: comedi: comedi_test: fix race when |
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2.6.32-longterm review patch. If anyone has any objections, please let me know.
------------------ cancelling command
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> Signed-off-by: Willy Tarreau <w@1wt.eu> --- 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 ef83a1a..7a1e2e8 100644 --- a/drivers/staging/comedi/drivers/comedi_test.c +++ b/drivers/staging/comedi/drivers/comedi_test.c @@ -450,7 +450,7 @@ 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; } -- 1.7.12.2.21.g234cd45.dirty
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