[PATCH 5.6 135/167] staging: comedi: Fix comedi_device refcnt leak in comedi_open

[Greg Kroah-Hartman]

From: Xiyu Yang <xiyuyang19@xxxxxxxxxxxx>

commit 332e0e17ad49e084b7db670ef43b5eb59abd9e34 upstream.

comedi_open() invokes comedi_dev_get_from_minor(), which returns a
reference of the COMEDI device to "dev" with increased refcount.

When comedi_open() returns, "dev" becomes invalid, so the refcount
should be decreased to keep refcount balanced.

The reference counting issue happens in one exception handling path of
comedi_open(). When "cfp" allocation is failed, the refcnt increased by
comedi_dev_get_from_minor() is not decreased, causing a refcnt leak.

Fix this issue by calling comedi_dev_put() on this error path when "cfp"
allocation is failed.

Fixes: 20f083c07565 ("staging: comedi: prepare support for per-file read and write subdevices")
Signed-off-by: Xiyu Yang <xiyuyang19@xxxxxxxxxxxx>
Cc: stable <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Xin Tan <tanxin.ctf@xxxxxxxxx>
Signed-off-by: Ian Abbott <abbotti@xxxxxxxxx>
Link: https://lore.kernel.org/r/1587361459-83622-1-git-send-email-xiyuyang19@xxxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/staging/comedi/comedi_fops.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/drivers/staging/comedi/comedi_fops.c
+++ b/drivers/staging/comedi/comedi_fops.c
@@ -2725,8 +2725,10 @@ static int comedi_open(struct inode *ino
 	}
 
 	cfp = kzalloc(sizeof(*cfp), GFP_KERNEL);
-	if (!cfp)
+	if (!cfp) {
+		comedi_dev_put(dev);
 		return -ENOMEM;
+	}
 
 	cfp->dev = dev;