vhost: Take a reference on the task in struct vhost_task.

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: vhost: Take a reference on the task in struct vhost_task. vhost_task_create() creates a task and keeps a reference to its task_struct. That task may exit early via a signal and its task_struct will be released. A pending vhost_task_wake() will then attempt to wake the task and access a task_struct which is no longer there. Acquire a reference on the task_struct while creating the thread and release the reference while the struct vhost_task itself is removed. If the task exits early due to a signal, then the vhost_task_wake() will still access a valid task_struct. The wake is safe and will be skipped in this case.

References

• https://git.kernel.org/stable/c/82a1463c968b1a6ae598a4f2fcef17b71bb7d3a0
• https://git.kernel.org/stable/c/d2be773a92874a070215b51b730cb2b1eaa8fae2
• https://git.kernel.org/stable/c/7ce635b3d3aba43296b62b5a2d97c008bc51cbd2
• https://git.kernel.org/stable/c/afe16653e05db07d658b55245c7a2e0603f136c0