iio: core: Prevent invalid memory access when there is no parent

BugLink: https://bugs.launchpad.net/bugs/2038969
commit b2a69969908fcaf68596dfc04369af0fe2e1d2f7 upstream.

Commit 813665564b3d ("iio: core: Convert to use firmware node handle
instead of OF node") switched the kind of nodes to use for label
retrieval in device registration.  Probably an unwanted change in that
commit was that if the device has no parent then NULL pointer is
accessed.  This is what happens in the stock IIO dummy driver when a
new entry is created in configfs:

  # mkdir /sys/kernel/config/iio/devices/dummy/foo
  BUG: kernel NULL pointer dereference, address: ...
  ...
  Call Trace:
  __iio_device_register
  iio_dummy_probe

Since there seems to be no reason to make a parent device of an IIO
dummy device mandatory, let’s prevent the invalid memory access in
__iio_device_register when the parent device is NULL.  With this
change, the IIO dummy driver works fine with configfs.

Fixes: 813665564b3d ("iio: core: Convert to use firmware node handle instead of OF node")
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Milan Zamazal <mzamazal@redhat.com>
Link: https://lore.kernel.org/r/20230719083208.88149-1-mzamazal@redhat.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

diff --git a/drivers/iio/industrialio-core.c b/drivers/iio/industrialio-core.c
index 52e690f031cb8794a0fd56c8a2a4062f77d29ae0..3ef6b62d842e9a358684cf16c4c562f8141da621 100644 (file)
--- a/drivers/iio/industrialio-core.c
+++ b/drivers/iio/industrialio-core.c
@@ -1916,7 +1916,7 @@ static const struct iio_buffer_setup_ops noop_ring_setup_ops;
 int __iio_device_register(struct iio_dev *indio_dev, struct module *this_mod)
 {
        struct iio_dev_opaque *iio_dev_opaque = to_iio_dev_opaque(indio_dev);
-       struct fwnode_handle *fwnode;
+       struct fwnode_handle *fwnode = NULL;
        int ret;
 
        if (!indio_dev->info)
@@ -1927,7 +1927,8 @@ int __iio_device_register(struct iio_dev *indio_dev, struct module *this_mod)
        /* If the calling driver did not initialize firmware node, do it here */
        if (dev_fwnode(&indio_dev->dev))
                fwnode = dev_fwnode(&indio_dev->dev);
-       else
+       /* The default dummy IIO device has no parent */
+       else if (indio_dev->dev.parent)
                fwnode = dev_fwnode(indio_dev->dev.parent);
        device_set_node(&indio_dev->dev, fwnode);