[PATCH 6.1.y] comedi: comedi_test: Fix possible deletion of uninitialized timers

[Sasha Levin <sashal@kernel.org>]

From: Ian Abbott <abbotti@mev.co.uk>

[ Upstream commit 1b98304c09a0192598d0767f1eb8c83d7e793091 ]

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>
[ replaced timer_delete_sync() with del_timer_sync() ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/comedi/drivers/comedi_test.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/comedi/drivers/comedi_test.c b/drivers/comedi/drivers/comedi_test.c
index 626d53bf9146a..aecb5f193be1b 100644
--- a/drivers/comedi/drivers/comedi_test.c
+++ b/drivers/comedi/drivers/comedi_test.c
@@ -788,7 +788,7 @@ 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);
 	}
-- 
2.39.5