Subject: CVE-2024-36027: btrfs: zoned: do not flag ZEROOUT on non-dirty extent buffer

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

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

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

btrfs: zoned: do not flag ZEROOUT on non-dirty extent buffer

Btrfs clears the content of an extent buffer marked as
EXTENT_BUFFER_ZONED_ZEROOUT before the bio submission. This mechanism is
introduced to prevent a write hole of an extent buffer, which is once
allocated, marked dirty, but turns out unnecessary and cleaned up within
one transaction operation.

Currently, btrfs_clear_buffer_dirty() marks the extent buffer as
EXTENT_BUFFER_ZONED_ZEROOUT, and skips the entry function. If this call
happens while the buffer is under IO (with the WRITEBACK flag set,
without the DIRTY flag), we can add the ZEROOUT flag and clear the
buffer's content just before a bio submission. As a result:

1) it can lead to adding faulty delayed reference item which leads to a
   FS corrupted (EUCLEAN) error, and

2) it writes out cleared tree node on disk

The former issue is previously discussed in [1]. The corruption happens
when it runs a delayed reference update. So, on-disk data is safe.

[1] https://lore.kernel.org/linux-btrfs/3f4f[email-masked]/

The latter one can reach on-disk data. But, as that node is already
processed by btrfs_clear_buffer_dirty(), that will be invalidated in the
next transaction commit anyway. So, the chance of hitting the corruption
is relatively small.

Anyway, we should skip flagging ZEROOUT on a non-DIRTY extent buffer, to
keep the content under IO intact.

The Linux kernel CVE team has assigned CVE-2024-36027 to this issue.

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

	Issue introduced in 6.8 with commit aa6313e6ff2b and fixed in 6.8.8 with commit f4b994fccbb6
	Issue introduced in 6.8 with commit aa6313e6ff2b and fixed in 6.9 with commit 68879386180c

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-2024-36027
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/btrfs/extent_io.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/f4b994fccbb6f294c4b31a6ca0114b09f7245043
	https://git.kernel.org/stable/c/68879386180c0efd5a11e800b0525a01068c9457