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.