CVE-2024-38580

In the Linux kernel, the following vulnerability has been resolved:
epoll: be better about file lifetimes
epoll can call out to vfs_poll() with a file pointer that may race with
the last ‘fput()’. That would make f_count go down to zero, and while
the ep->mtx locking means that the resulting file pointer tear-down will
be blocked until the poll returns, it means that f_count is already
dead, and any use of it won’t actually get a reference to the file any
more: it’s dead regardless.
Make sure we have a valid ref on the file pointer before we call down to
vfs_poll() from the epoll routines.