AZL-83666

In the Linux kernel, the following vulnerability has been resolved:

media: em28xx: fix use-after-free in em28xxv4l2open()

em28xxv4l2open() reads dev->v4l2 without holding dev->lock, creating a race with em28xxv4l2init()'s error path and em28xxv4l2fini(), both of which free the em28xx_v4l2 struct and set dev->v4l2 to NULL under dev->lock.

This race leads to two issues: - use-after-free in v4l2fhinit() when accessing vdev->ctrlhandler, since the videodevice is embedded in the freed em28xxv4l2 struct. - NULL pointer dereference in em28xxresolution_set() when accessing v4l2->norm, since dev->v4l2 has been set to NULL.

Fix this by moving the mutex_lock() before the dev->v4l2 read and adding a NULL check for dev->v4l2 under the lock.