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
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 da17d891f0e5d21f83e89689f139fb9c74b9bf7d..733e22c6852ed1d2f16b07ab916df3e12e1260ce 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) {
                timer_delete_sync(&devpriv->ai_timer);
                timer_delete_sync(&devpriv->ao_timer);
        }