io_uring: fix memory leak when removing provided buffers

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: io_uring: fix memory leak when removing provided buffers When removing provided buffers, io_buffer structs are not being disposed of, leading to a memory leak. They can't be freed individually, because they are allocated in page-sized groups. They need to be added to some free list instead, such as io_buffers_cache. All callers already hold the lock protecting it, apart from when destroying buffers, so had to extend the lock there.

References

• https://git.kernel.org/stable/c/ac48787f58d1068f4e06d627c1135784d64b4c72
• https://git.kernel.org/stable/c/c117c15927772d1624c29c092b6bd3f47c7faa48
• https://git.kernel.org/stable/c/b4a72c0589fdea6259720375426179888969d6a2