linux-cve-announce - CVE-2024-56755: netfs/fscache: Add a memory barrier for FSCACHE_VOLUME

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Message-ID: <2024122928-CVE-2024-56755-b189@gregkh>
Date: Sun, 29 Dec 2024 12:29:48 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: CVE-2024-56755: netfs/fscache: Add a memory barrier for FSCACHE_VOLUME_CREATING

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

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

netfs/fscache: Add a memory barrier for FSCACHE_VOLUME_CREATING

In fscache_create_volume(), there is a missing memory barrier between the
bit-clearing operation and the wake-up operation. This may cause a
situation where, after a wake-up, the bit-clearing operation hasn't been
detected yet, leading to an indefinite wait. The triggering process is as
follows:

  [cookie1]                [cookie2]                  [volume_work]
fscache_perform_lookup
  fscache_create_volume
                        fscache_perform_lookup
                          fscache_create_volume
			                        fscache_create_volume_work
                                                  cachefiles_acquire_volume
                                                  clear_and_wake_up_bit
    test_and_set_bit
                            test_and_set_bit
                              goto maybe_wait
      goto no_wait

In the above process, cookie1 and cookie2 has the same volume. When cookie1
enters the -no_wait- process, it will clear the bit and wake up the waiting
process. If a barrier is missing, it may cause cookie2 to remain in the
-wait- process indefinitely.

In commit 3288666c7256 ("fscache: Use clear_and_wake_up_bit() in
fscache_create_volume_work()"), barriers were added to similar operations
in fscache_create_volume_work(), but fscache_create_volume() was missed.

By combining the clear and wake operations into clear_and_wake_up_bit() to
fix this issue.

The Linux kernel CVE team has assigned CVE-2024-56755 to this issue.


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

	Issue introduced in 5.17 with commit bfa22da3ed652aa15acd4246fa13a0de6dbe4a59 and fixed in 6.1.120 with commit ddab02607eed9e415dc62fde421d4329e5345315
	Issue introduced in 5.17 with commit bfa22da3ed652aa15acd4246fa13a0de6dbe4a59 and fixed in 6.6.64 with commit 539fabba965e119b98066fc6ba5257b5eaf4eda2
	Issue introduced in 5.17 with commit bfa22da3ed652aa15acd4246fa13a0de6dbe4a59 and fixed in 6.11.11 with commit 8beb682cc9a0798a280bbb95e3e41617237090b2
	Issue introduced in 5.17 with commit bfa22da3ed652aa15acd4246fa13a0de6dbe4a59 and fixed in 6.12.2 with commit 8cc1df3113cb71a0df2c46dd5b102c9e11c8a8c6
	Issue introduced in 5.17 with commit bfa22da3ed652aa15acd4246fa13a0de6dbe4a59 and fixed in 6.13-rc1 with commit 22f9400a6f3560629478e0a64247b8fcc811a24d

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-2024-56755
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/netfs/fscache_volume.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/ddab02607eed9e415dc62fde421d4329e5345315
	https://git.kernel.org/stable/c/539fabba965e119b98066fc6ba5257b5eaf4eda2
	https://git.kernel.org/stable/c/8beb682cc9a0798a280bbb95e3e41617237090b2
	https://git.kernel.org/stable/c/8cc1df3113cb71a0df2c46dd5b102c9e11c8a8c6
	https://git.kernel.org/stable/c/22f9400a6f3560629478e0a64247b8fcc811a24d