linux-cve-announce - CVE-2024-56565: f2fs: fix to drop all discards after creating snapshot on lvm device

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Message-ID: <2024122714-CVE-2024-56565-1a08@gregkh>
Date: Fri, 27 Dec 2024 15:23:16 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: CVE-2024-56565: f2fs: fix to drop all discards after creating snapshot on lvm device

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

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

f2fs: fix to drop all discards after creating snapshot on lvm device

Piergiorgio reported a bug in bugzilla as below:

------------[ cut here ]------------
WARNING: CPU: 2 PID: 969 at fs/f2fs/segment.c:1330
RIP: 0010:__submit_discard_cmd+0x27d/0x400 [f2fs]
Call Trace:
 __issue_discard_cmd+0x1ca/0x350 [f2fs]
 issue_discard_thread+0x191/0x480 [f2fs]
 kthread+0xcf/0x100
 ret_from_fork+0x31/0x50
 ret_from_fork_asm+0x1a/0x30

w/ below testcase, it can reproduce this bug quickly:
- pvcreate /dev/vdb
- vgcreate myvg1 /dev/vdb
- lvcreate -L 1024m -n mylv1 myvg1
- mount /dev/myvg1/mylv1 /mnt/f2fs
- dd if=/dev/zero of=/mnt/f2fs/file bs=1M count=20
- sync
- rm /mnt/f2fs/file
- sync
- lvcreate -L 1024m -s -n mylv1-snapshot /dev/myvg1/mylv1
- umount /mnt/f2fs

The root cause is: it will update discard_max_bytes of mounted lvm
device to zero after creating snapshot on this lvm device, then,
__submit_discard_cmd() will pass parameter @nr_sects w/ zero value
to __blkdev_issue_discard(), it returns a NULL bio pointer, result
in panic.

This patch changes as below for fixing:
1. Let's drop all remained discards in f2fs_unfreeze() if snapshot
of lvm device is created.
2. Checking discard_max_bytes before submitting discard during
__submit_discard_cmd().

The Linux kernel CVE team has assigned CVE-2024-56565 to this issue.


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

	Issue introduced in 4.19 with commit 35ec7d5748849762008e8ae9f8ad2766229d5794 and fixed in 6.6.66 with commit ed24ab98242f8d22b66fbe0452c97751b5ea4e22
	Issue introduced in 4.19 with commit 35ec7d5748849762008e8ae9f8ad2766229d5794 and fixed in 6.12.4 with commit 15136c3861a3341db261ebdbb6ae4ae1765635e2
	Issue introduced in 4.19 with commit 35ec7d5748849762008e8ae9f8ad2766229d5794 and fixed in 6.13-rc1 with commit bc8aeb04fd80cb8cfae3058445c84410fd0beb5e

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-2024-56565
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/f2fs/segment.c
	fs/f2fs/super.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/ed24ab98242f8d22b66fbe0452c97751b5ea4e22
	https://git.kernel.org/stable/c/15136c3861a3341db261ebdbb6ae4ae1765635e2
	https://git.kernel.org/stable/c/bc8aeb04fd80cb8cfae3058445c84410fd0beb5e