[PATCH] staging: comedi: bug-fix NULL pointer dereference on failed attach

[Ian Abbott]

Commit dcd7b8bd63cb81c5b973bf86510ca3c80bbbd162 ("staging: comedi: put
module _after_ detach" by myself) reversed a couple of calls in
`comedi_device_attach()` when recovering from an error returned by the
low-level driver's 'attach' handler.  Unfortunately, that introduced a
NULL pointer dereference bug as `dev->driver` is NULL after the call to
`comedi_device_detach()`.   We still have a pointer to the low-level
comedi driver structure in the `driv` variable, so use that instead.

Signed-off-by: Ian Abbott <abbotti at mev.co.uk>
Cc: <stable at vger.kernel.org> # 3.10.x
Cc: <stable at vger.kernel.org> # 3.11.x
---
 drivers/staging/comedi/drivers.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/staging/comedi/drivers.c b/drivers/staging/comedi/drivers.c
index 60fd81c..317a821 100644
--- a/drivers/staging/comedi/drivers.c
+++ b/drivers/staging/comedi/drivers.c
@@ -537,7 +537,7 @@ int comedi_device_attach(struct comedi_device *dev, struct comedi_devconfig *it)
 		ret = comedi_device_postconfig(dev);
 	if (ret < 0) {
 		comedi_device_detach(dev);
-		module_put(dev->driver->module);
+		module_put(driv->module);
 	}
 	/* On success, the driver module count has been incremented. */
 out:
-- 
1.8.3.2