staging: comedi: amplc_dio200: fix possible NULL deref during detach

commit dfb2540e91e1f63765bc3ff497ad0b714d774261 upstream.

`dio200_detach()` is called by the comedi core to clean up if either
`dio200_attach()` or `dio200_attach_pci()` return an error.  It assigns
`thisboard` to the return value of `comedi_board(dev)` and assumes it is
non-null.  In the case of a previous call to `dio200_attach()` it won't
be `NULL` because the comedi core will have pointed it to one of the
elements of `dio200_boards[]`, but in the case of a previous call to
`dio200_attach_pci()` it could be `NULL`, leading to a null pointer
dereference.

Check that `thisboard` is valid at the top of `dio200_detach()` and
return early if it is `NULL`.  This is okay because the only other thing
that could have been allocated is `dev->private` and that is freed by
the comedi core, not by this function.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/staging/comedi/drivers/amplc_dio200.c b/drivers/staging/comedi/drivers/amplc_dio200.c
index cc8931fde839c491455ed10beaa56529480fbe2d..aee22fdd4e40a03ae5648a32d06cf8e592896d82 100644 (file)
--- a/drivers/staging/comedi/drivers/amplc_dio200.c
+++ b/drivers/staging/comedi/drivers/amplc_dio200.c
@@ -1429,6 +1429,8 @@ static void dio200_detach(struct comedi_device *dev)
        const struct dio200_layout_struct *layout;
        unsigned n;
 
+       if (!thisboard)
+               return;
        if (dev->irq)
                free_irq(dev->irq, dev);
        if (dev->subdevices) {