linux-cve-announce - CVE-2024-56549: cachefiles: Fix NULL pointer dereference in object->file

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Message-ID: <2024122730-CVE-2024-56549-ebcd@gregkh>
Date: Fri, 27 Dec 2024 15:11:40 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: CVE-2024-56549: cachefiles: Fix NULL pointer dereference in object->file

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

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

cachefiles: Fix NULL pointer dereference in object->file

At present, the object->file has the NULL pointer dereference problem in
ondemand-mode. The root cause is that the allocated fd and object->file
lifetime are inconsistent, and the user-space invocation to anon_fd uses
object->file. Following is the process that triggers the issue:

	  [write fd]				[umount]
cachefiles_ondemand_fd_write_iter
				       fscache_cookie_state_machine
					 cachefiles_withdraw_cookie
  if (!file) return -ENOBUFS
					   cachefiles_clean_up_object
					     cachefiles_unmark_inode_in_use
					     fput(object->file)
					     object->file = NULL
  // file NULL pointer dereference!
  __cachefiles_write(..., file, ...)

Fix this issue by add an additional reference count to the object->file
before write/llseek, and decrement after it finished.

The Linux kernel CVE team has assigned CVE-2024-56549 to this issue.


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

	Issue introduced in 5.19 with commit c8383054506c77b814489c09877b5db83fd4abf2 and fixed in 6.11.11 with commit f98770440c9bc468e2fd878212ec9526dbe08293
	Issue introduced in 5.19 with commit c8383054506c77b814489c09877b5db83fd4abf2 and fixed in 6.12.2 with commit 9582c7664103c9043e80a78f5c382aa6bdd67418
	Issue introduced in 5.19 with commit c8383054506c77b814489c09877b5db83fd4abf2 and fixed in 6.13-rc1 with commit 31ad74b20227ce6b40910ff78b1c604e42975cf1

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-2024-56549
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/interface.c
	fs/cachefiles/ondemand.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/f98770440c9bc468e2fd878212ec9526dbe08293
	https://git.kernel.org/stable/c/9582c7664103c9043e80a78f5c382aa6bdd67418
	https://git.kernel.org/stable/c/31ad74b20227ce6b40910ff78b1c604e42975cf1