linux-cve-announce - CVE-2025-21853: bpf: avoid holding freeze

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Message-ID: <2025031214-CVE-2025-21853-cf76@gregkh>
Date: Wed, 12 Mar 2025 10:42:19 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: CVE-2025-21853: bpf: avoid holding freeze_mutex during mmap operation

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

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

bpf: avoid holding freeze_mutex during mmap operation

We use map->freeze_mutex to prevent races between map_freeze() and
memory mapping BPF map contents with writable permissions. The way we
naively do this means we'll hold freeze_mutex for entire duration of all
the mm and VMA manipulations, which is completely unnecessary. This can
potentially also lead to deadlocks, as reported by syzbot in [0].

So, instead, hold freeze_mutex only during writeability checks, bump
(proactively) "write active" count for the map, unlock the mutex and
proceed with mmap logic. And only if something went wrong during mmap
logic, then undo that "write active" counter increment.

  [0] https://lore.kernel.org/bpf/678dcbc9.050a0220.303755.0066.GAE@google.com/

The Linux kernel CVE team has assigned CVE-2025-21853 to this issue.


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

	Issue introduced in 5.5 with commit fc9702273e2edb90400a34b3be76f7b08fa3344b and fixed in 6.6.80 with commit 29cfda62ab4d92ab94123813db49ab76c1e61b29
	Issue introduced in 5.5 with commit fc9702273e2edb90400a34b3be76f7b08fa3344b and fixed in 6.12.17 with commit d95607a5f2f9bb08194c9deaf4a5f3e8ba59a9d4
	Issue introduced in 5.5 with commit fc9702273e2edb90400a34b3be76f7b08fa3344b and fixed in 6.13.5 with commit 271e49f8a58edba65bc2b1250a0abaa98c4bfdbe
	Issue introduced in 5.5 with commit fc9702273e2edb90400a34b3be76f7b08fa3344b and fixed in 6.14-rc4 with commit bc27c52eea189e8f7492d40739b7746d67b65beb

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-2025-21853
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:
	kernel/bpf/syscall.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/29cfda62ab4d92ab94123813db49ab76c1e61b29
	https://git.kernel.org/stable/c/d95607a5f2f9bb08194c9deaf4a5f3e8ba59a9d4
	https://git.kernel.org/stable/c/271e49f8a58edba65bc2b1250a0abaa98c4bfdbe
	https://git.kernel.org/stable/c/bc27c52eea189e8f7492d40739b7746d67b65beb