cve/published/2024/CVE-2024-55642.mbox

From bippy-5f407fcff5a0 Mon Sep 17 00:00:00 2001
From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: <linux-cve-announce@vger.kernel.org>
Reply-to: <cve@kernel.org>, <linux-kernel@vger.kernel.org>
Subject: CVE-2024-55642: block: Prevent potential deadlocks in zone write plug error recovery

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

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

block: Prevent potential deadlocks in zone write plug error recovery

Zone write plugging for handling writes to zones of a zoned block
device always execute a zone report whenever a write BIO to a zone
fails. The intent of this is to ensure that the tracking of a zone write
pointer is always correct to ensure that the alignment to a zone write
pointer of write BIOs can be checked on submission and that we can
always correctly emulate zone append operations using regular write
BIOs.

However, this error recovery scheme introduces a potential deadlock if a
device queue freeze is initiated while BIOs are still plugged in a zone
write plug and one of these write operation fails. In such case, the
disk zone write plug error recovery work is scheduled and executes a
report zone. This in turn can result in a request allocation in the
underlying driver to issue the report zones command to the device. But
with the device queue freeze already started, this allocation will
block, preventing the report zone execution and the continuation of the
processing of the plugged BIOs. As plugged BIOs hold a queue usage
reference, the queue freeze itself will never complete, resulting in a
deadlock.

Avoid this problem by completely removing from the zone write plugging
code the use of report zones operations after a failed write operation,
instead relying on the device user to either execute a report zones,
reset the zone, finish the zone, or give up writing to the device (which
is a fairly common pattern for file systems which degrade to read-only
after write failures). This is not an unreasonnable requirement as all
well-behaved applications, FSes and device mapper already use report
zones to recover from write errors whenever possible by comparing the
current position of a zone write pointer with what their assumption
about the position is.

The changes to remove the automatic error recovery are as follows:
 - Completely remove the error recovery work and its associated
   resources (zone write plug list head, disk error list, and disk
   zone_wplugs_work work struct). This also removes the functions
   disk_zone_wplug_set_error() and disk_zone_wplug_clear_error().

 - Change the BLK_ZONE_WPLUG_ERROR zone write plug flag into
   BLK_ZONE_WPLUG_NEED_WP_UPDATE. This new flag is set for a zone write
   plug whenever a write opration targetting the zone of the zone write
   plug fails. This flag indicates that the zone write pointer offset is
   not reliable and that it must be updated when the next report zone,
   reset zone, finish zone or disk revalidation is executed.

 - Modify blk_zone_write_plug_bio_endio() to set the
   BLK_ZONE_WPLUG_NEED_WP_UPDATE flag for the target zone of a failed
   write BIO.

 - Modify the function disk_zone_wplug_set_wp_offset() to clear this
   new flag, thus implementing recovery of a correct write pointer
   offset with the reset (all) zone and finish zone operations.

 - Modify blkdev_report_zones() to always use the disk_report_zones_cb()
   callback so that disk_zone_wplug_sync_wp_offset() can be called for
   any zone marked with the BLK_ZONE_WPLUG_NEED_WP_UPDATE flag.
   This implements recovery of a correct write pointer offset for zone
   write plugs marked with BLK_ZONE_WPLUG_NEED_WP_UPDATE and within
   the range of the report zones operation executed by the user.

 - Modify blk_revalidate_seq_zone() to call
   disk_zone_wplug_sync_wp_offset() for all sequential write required
   zones when a zoned block device is revalidated, thus always resolving
   any inconsistency between the write pointer offset of zone write
   plugs and the actual write pointer position of sequential zones.

The Linux kernel CVE team has assigned CVE-2024-55642 to this issue.


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

	Issue introduced in 6.10 with commit dd291d77cc90eb6a86e9860ba8e6e38eebd57d12 and fixed in 6.12.6 with commit 7fa80134cf266325fa61139320091001c9b3c477
	Issue introduced in 6.10 with commit dd291d77cc90eb6a86e9860ba8e6e38eebd57d12 and fixed in 6.13 with commit fe0418eb9bd69a19a948b297c8de815e05f3cde1

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-2024-55642
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:
	block/blk-zoned.c
	include/linux/blkdev.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/7fa80134cf266325fa61139320091001c9b3c477
	https://git.kernel.org/stable/c/fe0418eb9bd69a19a948b297c8de815e05f3cde1