Subject: CVE-2024-26878: quota: Fix potential NULL pointer dereference

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

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

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

quota: Fix potential NULL pointer dereference

Below race may cause NULL pointer dereference

P1					P2
dquot_free_inode			quota_off
					  drop_dquot_ref
					   remove_dquot_ref
					   dquots = i_dquot(inode)
  dquots = i_dquot(inode)
  srcu_read_lock
  dquots[cnt]) != NULL (1)
					     dquots[type] = NULL (2)
  spin_lock(&dquots[cnt]->dq_dqb_lock) (3)
   ....

If dquot_free_inode(or other routines) checks inode's quota pointers (1)
before quota_off sets it to NULL(2) and use it (3) after that, NULL pointer
dereference will be triggered.

So let's fix it by using a temporary pointer to avoid this issue.

The Linux kernel CVE team has assigned CVE-2024-26878 to this issue.

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

	Fixed in 4.19.311 with commit 8514899c1a4e
	Fixed in 5.4.273 with commit 49669f8e7eb0
	Fixed in 5.10.214 with commit 61380537aa6d
	Fixed in 5.15.153 with commit 1ca72a3de915
	Fixed in 6.1.83 with commit 7f9e833fc0f9
	Fixed in 6.6.23 with commit 40a673b4b07e
	Fixed in 6.7.11 with commit f2649d98aa9c
	Fixed in 6.8.2 with commit 6afc9f4434fa
	Fixed in 6.9 with commit d0aa72604fbd

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-2024-26878
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/quota/dquot.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/8514899c1a4edf802f03c408db901063aa3f05a1
	https://git.kernel.org/stable/c/49669f8e7eb053f91d239df7b1bfb4500255a9d0
	https://git.kernel.org/stable/c/61380537aa6dd32d8a723d98b8f1bd1b11d8fee0
	https://git.kernel.org/stable/c/1ca72a3de915f87232c9a4cb9bebbd3af8ed3e25
	https://git.kernel.org/stable/c/7f9e833fc0f9b47be503af012eb5903086939754
	https://git.kernel.org/stable/c/40a673b4b07efd6f74ff3ab60f38b26aa91ee5d5
	https://git.kernel.org/stable/c/f2649d98aa9ca8623149b3cb8df00c944f5655c7
	https://git.kernel.org/stable/c/6afc9f4434fa8063aa768c2bf5bf98583aee0877
	https://git.kernel.org/stable/c/d0aa72604fbd80c8aabb46eda00535ed35570f1f