staging: greybus: light: fix a couple double frees

The problem is in gb_lights_request_handler().  If we get a request to
change the config then we release the light with gb_lights_light_release()
and re-allocated it.  However, if the allocation fails part way through
then we call gb_lights_light_release() again.  This can lead to a couple
different double frees where we haven't cleared out the original values:

	gb_lights_light_v4l2_unregister(light);
	...
	kfree(light->channels);
	kfree(light->name);

I also made a small change to how we set "light->channels_count = 0;".
The original code handled this part fine and did not cause a use after
free but it was sort of complicated to read.

Fixes: 2870b52bae4c ("greybus: lights: add lights implementation")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Rui Miguel Silva <rmfrfs@gmail.com>
Link: https://lore.kernel.org/r/20190829122839.GA20116@mwanda
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/staging/greybus/light.c b/drivers/staging/greybus/light.c
index b3b1b25..d6ba25f 100644 (file)
--- a/drivers/staging/greybus/light.c
+++ b/drivers/staging/greybus/light.c
@@ -1096,21 +1096,21 @@ static void gb_lights_channel_release(struct gb_channel *channel)
 static void gb_lights_light_release(struct gb_light *light)
 {
        int i;
-       int count;
 
        light->ready = false;
 
-       count = light->channels_count;
-
        if (light->has_flash)
                gb_lights_light_v4l2_unregister(light);
+       light->has_flash = false;
 
-       for (i = 0; i < count; i++) {
+       for (i = 0; i < light->channels_count; i++)
                gb_lights_channel_release(&light->channels[i]);
-               light->channels_count--;
-       }
+       light->channels_count = 0;
+
        kfree(light->channels);
+       light->channels = NULL;
        kfree(light->name);
+       light->name = NULL;
 }
 
 static void gb_lights_release(struct gb_lights *glights)