staging: comedi: prevent auto-unconfig of manually configured devices

When a low-level comedi driver auto-configures a device, a `struct
comedi_dev_file_info` is allocated (as well as a `struct
comedi_device`) by `comedi_alloc_board_minor()`.  A pointer to the
hardware `struct device` is stored as a cookie in the `struct
comedi_dev_file_info`.  When the low-level comedi driver
auto-unconfigures the device, `comedi_auto_unconfig()` uses the cookie
to find the `struct comedi_dev_file_info` so it can detach the comedi
device from the driver, clean it up and free it.

A problem arises if the user manually unconfigures and reconfigures the
comedi device using the `COMEDI_DEVCONFIG` ioctl so that is no longer
associated with the original hardware device.  The problem is that the
cookie is not cleared, so that a call to `comedi_auto_unconfig()` from
the low-level driver will still find it, detach it, clean it up and free
it.

Stop this problem occurring by always clearing the `hardware_device`
cookie in the `struct comedi_dev_file_info` whenever the
`COMEDI_DEVCONFIG` ioctl call is successful.

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

1 files changed, 3 insertions, 0 deletions

diff --git a/drivers/staging/comedi/comedi_fops.c b/drivers/staging/comedi/comedi_fops.c
index b7bba1790a20..9b038e4a7e71 100644
--- a/drivers/staging/comedi/comedi_fops.c
+++ b/drivers/staging/comedi/comedi_fops.c
@@ -1549,6 +1549,9 @@ static long comedi_unlocked_ioctl(struct file *file, unsigned int cmd,
         if (cmd == COMEDI_DEVCONFIG) {
                 rc = do_devconfig_ioctl(dev,
                                         (struct comedi_devconfig __user *)arg);
+                if (rc == 0)
+                        /* Evade comedi_auto_unconfig(). */
+                        dev_file_info->hardware_device = NULL;
                 goto done;
         }