Subject: CVE-2024-40935: cachefiles: flush all requests after setting CACHEFILES_DEAD

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

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

In the Linux kernel, the following vulnerability has been resolved:

cachefiles: flush all requests after setting CACHEFILES_DEAD

In ondemand mode, when the daemon is processing an open request, if the
kernel flags the cache as CACHEFILES_DEAD, the cachefiles_daemon_write()
will always return -EIO, so the daemon can't pass the copen to the kernel.
Then the kernel process that is waiting for the copen triggers a hung_task.

Since the DEAD state is irreversible, it can only be exited by closing
/dev/cachefiles. Therefore, after calling cachefiles_io_error() to mark
the cache as CACHEFILES_DEAD, if in ondemand mode, flush all requests to
avoid the above hungtask. We may still be able to read some of the cached
data before closing the fd of /dev/cachefiles.

Note that this relies on the patch that adds reference counting to the req,
otherwise it may UAF.

The Linux kernel CVE team has assigned CVE-2024-40935 to this issue.

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

	Issue introduced in 5.19 with commit c8383054506c and fixed in 6.1.95 with commit 320ba9cbca78
	Issue introduced in 5.19 with commit c8383054506c and fixed in 6.6.35 with commit 3bf0b8030296
	Issue introduced in 5.19 with commit c8383054506c and fixed in 6.9.6 with commit e73fac950848
	Issue introduced in 5.19 with commit c8383054506c and fixed in 6.10 with commit 85e833cd7243

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-2024-40935
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/cachefiles/daemon.c
	fs/cachefiles/internal.h

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/320ba9cbca78be79c912143bbba1d1b35ca55cf0
	https://git.kernel.org/stable/c/3bf0b8030296e9ee60d3d4c15849ad9ac0b47081
	https://git.kernel.org/stable/c/e73fac95084839c5178d97e81c6a2051251bdc00
	https://git.kernel.org/stable/c/85e833cd7243bda7285492b0653c3abb1e2e757b