Subject: CVE-2024-38580: epoll: be better about file lifetimes

From: Greg Kroah-Hartman <[email-masked]>

Description
===========

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.

The Linux kernel CVE team has assigned CVE-2024-38580 to this issue.

Affected and fixed versions
===========================

	Fixed in 5.15.161 with commit cbfd1088e24e
	Fixed in 6.1.93 with commit 559214eb4e5c
	Fixed in 6.6.33 with commit 4f65f4defe4e
	Fixed in 6.8.12 with commit 16e3182f6322
	Fixed in 6.9 with commit 4efaa5acf0a1

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2024-38580
will be updated if fixes are backported, please check that for the most
up to date information about this issue.

Affected files
==============

The file(s) affected by this issue are:
	fs/eventpoll.c

Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/cbfd1088e24ec4c1199756a37cb8e4cd0a4b016e
	https://git.kernel.org/stable/c/559214eb4e5c3d05e69428af2fae2691ba1eb784
	https://git.kernel.org/stable/c/4f65f4defe4e23659275ce5153541cd4f76ce2d2
	https://git.kernel.org/stable/c/16e3182f6322575eb7c12e728ad3c7986a189d5d
	https://git.kernel.org/stable/c/4efaa5acf0a1d2b5947f98abb3acf8bfd966422b