linux-cve-announce - CVE-2025-68198: crash: fix crashkernel resource shrink

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Message-ID: <2025121627-CVE-2025-68198-2638@gregkh>
Date: Tue, 16 Dec 2025 14:54:27 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2025-68198: crash: fix crashkernel resource shrink

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

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

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

crash: fix crashkernel resource shrink

When crashkernel is configured with a high reservation, shrinking its
value below the low crashkernel reservation causes two issues:

1. Invalid crashkernel resource objects
2. Kernel crash if crashkernel shrinking is done twice

For example, with crashkernel=200M,high, the kernel reserves 200MB of high
memory and some default low memory (say 256MB).  The reservation appears
as:

cat /proc/iomem | grep -i crash
af000000-beffffff : Crash kernel
433000000-43f7fffff : Crash kernel

If crashkernel is then shrunk to 50MB (echo 52428800 >
/sys/kernel/kexec_crash_size), /proc/iomem still shows 256MB reserved:
af000000-beffffff : Crash kernel

Instead, it should show 50MB:
af000000-b21fffff : Crash kernel

Further shrinking crashkernel to 40MB causes a kernel crash with the
following trace (x86):

BUG: kernel NULL pointer dereference, address: 0000000000000038
PGD 0 P4D 0
Oops: 0000 [#1] PREEMPT SMP NOPTI
<snip...>
Call Trace: <TASK>
? __die_body.cold+0x19/0x27
? page_fault_oops+0x15a/0x2f0
? search_module_extables+0x19/0x60
? search_bpf_extables+0x5f/0x80
? exc_page_fault+0x7e/0x180
? asm_exc_page_fault+0x26/0x30
? __release_resource+0xd/0xb0
release_resource+0x26/0x40
__crash_shrink_memory+0xe5/0x110
crash_shrink_memory+0x12a/0x190
kexec_crash_size_store+0x41/0x80
kernfs_fop_write_iter+0x141/0x1f0
vfs_write+0x294/0x460
ksys_write+0x6d/0xf0
<snip...>

This happens because __crash_shrink_memory()/kernel/crash_core.c
incorrectly updates the crashk_res resource object even when
crashk_low_res should be updated.

Fix this by ensuring the correct crashkernel resource object is updated
when shrinking crashkernel memory.

The Linux kernel CVE team has assigned CVE-2025-68198 to this issue.


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

	Issue introduced in 6.5 with commit 16c6006af4d4e70ecef93977a5314409d931020b and fixed in 6.6.118 with commit f01f9c348d76d40bf104a94449e3ce4057fdefee
	Issue introduced in 6.5 with commit 16c6006af4d4e70ecef93977a5314409d931020b and fixed in 6.12.59 with commit f89c5e7077f63e45e8ba5a77b7cf0803130367e6
	Issue introduced in 6.5 with commit 16c6006af4d4e70ecef93977a5314409d931020b and fixed in 6.17.9 with commit a2bd247f8c6c5ac3f0ba823a2fffd77bb9cdf618
	Issue introduced in 6.5 with commit 16c6006af4d4e70ecef93977a5314409d931020b and fixed in 6.18 with commit 00fbff75c5acb4755f06f08bd1071879c63940c5

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-2025-68198
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/crash_core.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/f01f9c348d76d40bf104a94449e3ce4057fdefee
	https://git.kernel.org/stable/c/f89c5e7077f63e45e8ba5a77b7cf0803130367e6
	https://git.kernel.org/stable/c/a2bd247f8c6c5ac3f0ba823a2fffd77bb9cdf618
	https://git.kernel.org/stable/c/00fbff75c5acb4755f06f08bd1071879c63940c5