comedi: comedi_test: Fix possible deletion of uninitialized timers

commit 1b98304c09a0192598d0767f1eb8c83d7e793091 upstream.

In `waveform_common_attach()`, the two timers `&devpriv->ai_timer` and
`&devpriv->ao_timer` are initialized after the allocation of the device
private data by `comedi_alloc_devpriv()` and the subdevices by
`comedi_alloc_subdevices()`.  The function may return with an error
between those function calls.  In that case, `waveform_detach()` will be
called by the Comedi core to clean up.  The check that
`waveform_detach()` uses to decide whether to delete the timers is
incorrect.  It only checks that the device private data was allocated,
but that does not guarantee that the timers were initialized.  It also
needs to check that the subdevices were allocated.  Fix it.

Fixes: 73e0e4dfed4c ("staging: comedi: comedi_test: fix timer lock-up")
Cc: stable@vger.kernel.org # 6.15+
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Link: https://lore.kernel.org/r/20250708130627.21743-1-abbotti@mev.co.uk
[ changed timer_delete_sync() to del_timer_sync() ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/comedi/drivers/comedi_test.c b/drivers/comedi/drivers/comedi_test.c
index 05ae9122823f8032bf62d8e7cd1f7570115a04f8..e713ef611434da34e3f030a76ab5b69b47ffcbf4 100644 (file)
--- a/drivers/comedi/drivers/comedi_test.c
+++ b/drivers/comedi/drivers/comedi_test.c
@@ -790,7 +790,7 @@ static void waveform_detach(struct comedi_device *dev)
 {
        struct waveform_private *devpriv = dev->private;
 
-       if (devpriv) {
+       if (devpriv && dev->n_subdevices) {
                del_timer_sync(&devpriv->ai_timer);
                del_timer_sync(&devpriv->ao_timer);
        }