linux-cve-announce - CVE-2025-21709: kernel: be more careful about dup

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Message-ID: <2025022643-CVE-2025-21709-e967@gregkh>
Date: Wed, 26 Feb 2025 18:06:04 -0800
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: CVE-2025-21709: kernel: be more careful about dup_mmap() failures and uprobe registering

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

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

kernel: be more careful about dup_mmap() failures and uprobe registering

If a memory allocation fails during dup_mmap(), the maple tree can be left
in an unsafe state for other iterators besides the exit path.  All the
locks are dropped before the exit_mmap() call (in mm/mmap.c), but the
incomplete mm_struct can be reached through (at least) the rmap finding
the vmas which have a pointer back to the mm_struct.

Up to this point, there have been no issues with being able to find an
mm_struct that was only partially initialised.  Syzbot was able to make
the incomplete mm_struct fail with recent forking changes, so it has been
proven unsafe to use the mm_struct that hasn't been initialised, as
referenced in the link below.

Although 8ac662f5da19f ("fork: avoid inappropriate uprobe access to
invalid mm") fixed the uprobe access, it does not completely remove the
race.

This patch sets the MMF_OOM_SKIP to avoid the iteration of the vmas on the
oom side (even though this is extremely unlikely to be selected as an oom
victim in the race window), and sets MMF_UNSTABLE to avoid other potential
users from using a partially initialised mm_struct.

When registering vmas for uprobe, skip the vmas in an mm that is marked
unstable.  Modifying a vma in an unstable mm may cause issues if the mm
isn't fully initialised.

The Linux kernel CVE team has assigned CVE-2025-21709 to this issue.

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

	Issue introduced in 6.8 with commit d2406291483775ecddaee929231a39c70c08fda2 and fixed in 6.13.2 with commit da139948aeda677ac09cc0e7d837f8a314de7d55
	Issue introduced in 6.8 with commit d2406291483775ecddaee929231a39c70c08fda2 and fixed in 6.14-rc1 with commit 64c37e134b120fb462fb4a80694bfb8e7be77b14

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-2025-21709
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/events/uprobes.c
	kernel/fork.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/da139948aeda677ac09cc0e7d837f8a314de7d55
	https://git.kernel.org/stable/c/64c37e134b120fb462fb4a80694bfb8e7be77b14