On 2/22/19 12:32 PM, Laurent Pinchart wrote:
> Hi Hans,
>
> Thank you for the patch.
>
> On Thu, Feb 21, 2019 at 03:21:47PM +0100, Hans Verkuil wrote:
>> When the v4l-subdev device node is released it calls the
>> v4l2_device_release_subdev_node() function which sets sd->devnode
>> to NULL.
>>
>> However, the v4l2_subdev struct may already be released causing this
>> to write in freed memory.
>>
>> Instead just use the regular video_device_release release function
>> (just calls kfree) and set sd->devnode to NULL right after the
>> video_unregister_device() call.
>
> This seems a bit of a workaround. The devnode can access the subdev in
> multiple ways, it should really keep a reference to the subdev to ensure
> it doesn't get freed early.
It's not the link from the devnode to the subdev (that's done through
video_get_drvdata()), it's the link from the subdev to the devnode.
As soon as the video device is unregistered sd->devnode should be set
to NULL. It is in fact how sd->devnode is used: as a check if the devnode
was registered.
The only other place where it is used is in v4l2_subdev_notify_event to
send an event to the devnode, and after unregistering the video device
you no longer want to do that, so setting sd->devnode to NULL after it
is unregistered is the right thing to do.
FYI, I'll post a v2 of this series soon.
Regards,
Hans
>
>> Signed-off-by: Hans Verkuil <hverkuil-cisco@xxxxxxxxx>
>> ---
>> drivers/media/v4l2-core/v4l2-device.c | 10 ++--------
>> 1 file changed, 2 insertions(+), 8 deletions(-)
>>
>> diff --git a/drivers/media/v4l2-core/v4l2-device.c b/drivers/media/v4l2-core/v4l2-device.c
>> index e0ddb9a52bd1..57a7b220fa4d 100644
>> --- a/drivers/media/v4l2-core/v4l2-device.c
>> +++ b/drivers/media/v4l2-core/v4l2-device.c
>> @@ -216,13 +216,6 @@ int v4l2_device_register_subdev(struct v4l2_device *v4l2_dev,
>> }
>> EXPORT_SYMBOL_GPL(v4l2_device_register_subdev);
>>
>> -static void v4l2_device_release_subdev_node(struct video_device *vdev)
>> -{
>> - struct v4l2_subdev *sd = video_get_drvdata(vdev);
>> - sd->devnode = NULL;
>> - kfree(vdev);
>> -}
>> -
>> int v4l2_device_register_subdev_nodes(struct v4l2_device *v4l2_dev)
>> {
>> struct video_device *vdev;
>> @@ -250,7 +243,7 @@ int v4l2_device_register_subdev_nodes(struct v4l2_device *v4l2_dev)
>> vdev->dev_parent = sd->dev;
>> vdev->v4l2_dev = v4l2_dev;
>> vdev->fops = &v4l2_subdev_fops;
>> - vdev->release = v4l2_device_release_subdev_node;
>> + vdev->release = video_device_release;
>> vdev->ctrl_handler = sd->ctrl_handler;
>> err = __video_register_device(vdev, VFL_TYPE_SUBDEV, -1, 1,
>> sd->owner);
>> @@ -319,6 +312,7 @@ void v4l2_device_unregister_subdev(struct v4l2_subdev *sd)
>> }
>> #endif
>> video_unregister_device(sd->devnode);
>> + sd->devnode = NULL;
>> if (!sd->owner_v4l2_dev)
>> module_put(sd->owner);
>> }
>
