linux-cve-announce - CVE-2025-38073: block: fix race between set

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Message-ID: <2025061839-CVE-2025-38073-4f76@gregkh>
Date: Wed, 18 Jun 2025 11:34:08 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2025-38073: block: fix race between set_blocksize and read paths

From: Greg Kroah-Hartman <gregkh@...nel.org>

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

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

block: fix race between set_blocksize and read paths

With the new large sector size support, it's now the case that
set_blocksize can change i_blksize and the folio order in a manner that
conflicts with a concurrent reader and causes a kernel crash.

Specifically, let's say that udev-worker calls libblkid to detect the
labels on a block device.  The read call can create an order-0 folio to
read the first 4096 bytes from the disk.  But then udev is preempted.

Next, someone tries to mount an 8k-sectorsize filesystem from the same
block device.  The filesystem calls set_blksize, which sets i_blksize to
8192 and the minimum folio order to 1.

Now udev resumes, still holding the order-0 folio it allocated.  It then
tries to schedule a read bio and do_mpage_readahead tries to create
bufferheads for the folio.  Unfortunately, blocks_per_folio == 0 because
the page size is 4096 but the blocksize is 8192 so no bufferheads are
attached and the bh walk never sets bdev.  We then submit the bio with a
NULL block device and crash.

Therefore, truncate the page cache after flushing but before updating
i_blksize.  However, that's not enough -- we also need to lock out file
IO and page faults during the update.  Take both the i_rwsem and the
invalidate_lock in exclusive mode for invalidations, and in shared mode
for read/write operations.

I don't know if this is the correct fix, but xfs/259 found it.

The Linux kernel CVE team has assigned CVE-2025-38073 to this issue.

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

	Fixed in 6.12.31 with commit 64f505b08e0cfd8163491c8c082d4f47a88e51d4
	Fixed in 6.14.9 with commit 8c5cf440a378801d313eb58be996fdc81a8878a4
	Fixed in 6.15 with commit c0e473a0d226479e8e925d5ba93f751d8df628e9

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-2025-38073
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/bdev.c
	block/blk-zoned.c
	block/fops.c
	block/ioctl.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/64f505b08e0cfd8163491c8c082d4f47a88e51d4
	https://git.kernel.org/stable/c/8c5cf440a378801d313eb58be996fdc81a8878a4
	https://git.kernel.org/stable/c/c0e473a0d226479e8e925d5ba93f751d8df628e9