linux-kernel - [PATCH] comedi: comedi_test: Fix possible deletion of uninitialized timers

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Message-ID: <20250708130627.21743-1-abbotti@mev.co.uk>
Date: Tue,  8 Jul 2025 14:06:27 +0100
From: Ian Abbott <abbotti@....co.uk>
To: linux-kernel@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Ian Abbott <abbotti@....co.uk>,
	H Hartley Sweeten <hsweeten@...ionengravers.com>,
	stable@...r.kernel.org
Subject: [PATCH] comedi: comedi_test: Fix possible deletion of uninitialized timers

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@...r.kernel.org> # 6.15+
Signed-off-by: Ian Abbott <abbotti@....co.uk>
---
Patch fails to apply to kernels before 6.15, requiring backports.
---
 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 9747e6d1f6eb..7984950f0f99 100644
--- a/drivers/comedi/drivers/comedi_test.c
+++ b/drivers/comedi/drivers/comedi_test.c
@@ -792,7 +792,7 @@ 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);
 	}
-- 
2.47.2