[PATCH v3] iio: core: fix double free in iio_device_unregister_sysfs()

[Yang Yingliang]

I got the double free report:

BUG: KASAN: double-free or invalid-free in kfree+0xce/0x390
 kfree+0xce/0x390
 iio_device_unregister_sysfs+0x108/0x13b [industrialio]
 iio_dev_release+0x9e/0x10e [industrialio]
 device_release+0xa5/0x240
 kobject_put+0x1e5/0x540
 put_device+0x20/0x30
 devm_iio_device_release+0x21/0x30 [industrialio]

If __iio_device_register() fails, iio_dev_opaque->groups will be freed
in error path in iio_device_unregister_sysfs(), then iio_dev_release()
will call iio_device_unregister_sysfs() again, it causes double free.
Set iio_dev_opaque->groups to NULL when it's freed to fix this double free.

Fixes: 32f171724e5c ("iio: core: rework iio device group creation")
Reported-by: Hulk Robot <hulkci@xxxxxxxxxx>
Reviewed-by: Alexandru Ardelean <ardeleanalex@xxxxxxxxx>
Signed-off-by: Yang Yingliang <yangyingliang@xxxxxxxxxx>
---
v1 -> v3:
  reduce some backtrace in commit message
---
 drivers/iio/industrialio-core.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/iio/industrialio-core.c b/drivers/iio/industrialio-core.c
index 2dbb37e09b8c..2dc837db50f7 100644
--- a/drivers/iio/industrialio-core.c
+++ b/drivers/iio/industrialio-core.c
@@ -1600,6 +1600,7 @@ static void iio_device_unregister_sysfs(struct iio_dev *indio_dev)
 	kfree(iio_dev_opaque->chan_attr_group.attrs);
 	iio_dev_opaque->chan_attr_group.attrs = NULL;
 	kfree(iio_dev_opaque->groups);
+	iio_dev_opaque->groups = NULL;
 }
 
 static void iio_dev_release(struct device *device)
-- 
2.25.1