linux-cve-announce - CVE-2024-42149: fs: don't misleadingly warn during thaw operations

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Message-ID: <2024073033-CVE-2024-42149-c08b@gregkh>
Date: Tue, 30 Jul 2024 09:48:07 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: CVE-2024-42149: fs: don't misleadingly warn during thaw operations

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

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

fs: don't misleadingly warn during thaw operations

The block device may have been frozen before it was claimed by a
filesystem. Concurrently another process might try to mount that
frozen block device and has temporarily claimed the block device for
that purpose causing a concurrent fs_bdev_thaw() to end up here. The
mounter is already about to abort mounting because they still saw an
elevanted bdev->bd_fsfreeze_count so get_bdev_super() will return
NULL in that case.

For example, P1 calls dm_suspend() which calls into bdev_freeze() before
the block device has been claimed by the filesystem. This brings
bdev->bd_fsfreeze_count to 1 and no call into fs_bdev_freeze() is
required.

Now P2 tries to mount that frozen block device. It claims it and checks
bdev->bd_fsfreeze_count. As it's elevated it aborts mounting.

In the meantime P3 called dm_resume(). P3 sees that the block device is
already claimed by a filesystem and calls into fs_bdev_thaw().

P3 takes a passive reference and realizes that the filesystem isn't
ready yet. P3 puts itself to sleep to wait for the filesystem to become
ready.

P2 now puts the last active reference to the filesystem and marks it as
dying. P3 gets woken, sees that the filesystem is dying and
get_bdev_super() fails.

The Linux kernel CVE team has assigned CVE-2024-42149 to this issue.

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

	Issue introduced in 6.8 with commit 49ef8832fb1a and fixed in 6.9.9 with commit 25b1e3906e05
	Issue introduced in 6.8 with commit 49ef8832fb1a and fixed in 6.10 with commit 2ae4db5647d8

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-2024-42149
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/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/25b1e3906e050d452427bc51620bb7f0a591373a
	https://git.kernel.org/stable/c/2ae4db5647d807efb6a87c09efaa6d1db9c905d7