linux-cve-announce - CVE-2025-40009: fs/proc/task_mmu: check p->vec

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Message-ID: <2025102002-CVE-2025-40009-5a08@gregkh>
Date: Mon, 20 Oct 2025 17:27:05 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2025-40009: fs/proc/task_mmu: check p->vec_buf for NULL

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

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

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

fs/proc/task_mmu: check p->vec_buf for NULL

When the PAGEMAP_SCAN ioctl is invoked with vec_len = 0 reaches
pagemap_scan_backout_range(), kernel panics with null-ptr-deref:

[   44.936808] Oops: general protection fault, probably for non-canonical address 0xdffffc0000000000: 0000 [#1] SMP DEBUG_PAGEALLOC KASAN NOPTI
[   44.937797] KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]
[   44.938391] CPU: 1 UID: 0 PID: 2480 Comm: reproducer Not tainted 6.17.0-rc6 #22 PREEMPT(none)
[   44.939062] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[   44.939935] RIP: 0010:pagemap_scan_thp_entry.isra.0+0x741/0xa80

<snip registers, unreliable trace>

[   44.946828] Call Trace:
[   44.947030]  <TASK>
[   44.949219]  pagemap_scan_pmd_entry+0xec/0xfa0
[   44.952593]  walk_pmd_range.isra.0+0x302/0x910
[   44.954069]  walk_pud_range.isra.0+0x419/0x790
[   44.954427]  walk_p4d_range+0x41e/0x620
[   44.954743]  walk_pgd_range+0x31e/0x630
[   44.955057]  __walk_page_range+0x160/0x670
[   44.956883]  walk_page_range_mm+0x408/0x980
[   44.958677]  walk_page_range+0x66/0x90
[   44.958984]  do_pagemap_scan+0x28d/0x9c0
[   44.961833]  do_pagemap_cmd+0x59/0x80
[   44.962484]  __x64_sys_ioctl+0x18d/0x210
[   44.962804]  do_syscall_64+0x5b/0x290
[   44.963111]  entry_SYSCALL_64_after_hwframe+0x76/0x7e

vec_len = 0 in pagemap_scan_init_bounce_buffer() means no buffers are
allocated and p->vec_buf remains set to NULL.

This breaks an assumption made later in pagemap_scan_backout_range(), that
page_region is always allocated for p->vec_buf_index.

Fix it by explicitly checking p->vec_buf for NULL before dereferencing.

Other sites that might run into same deref-issue are already (directly or
transitively) protected by checking p->vec_buf.

Note:
>>From PAGEMAP_SCAN man page, it seems vec_len = 0 is valid when no output
is requested and it's only the side effects caller is interested in,
hence it passes check in pagemap_scan_get_args().

This issue was found by syzkaller.

The Linux kernel CVE team has assigned CVE-2025-40009 to this issue.


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

	Issue introduced in 6.7 with commit 52526ca7fdb905a768a93f8faa418e9b988fc34b and fixed in 6.12.50 with commit ca988dcdc6683ecd9de5f525ce469588a9141c21
	Issue introduced in 6.7 with commit 52526ca7fdb905a768a93f8faa418e9b988fc34b and fixed in 6.16.10 with commit a2cb8818a3d915cd33a1e8b2babc1bb0c34862c3
	Issue introduced in 6.7 with commit 52526ca7fdb905a768a93f8faa418e9b988fc34b and fixed in 6.17 with commit 28aa29986dde79e8466bc87569141291053833f5

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-2025-40009
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/proc/task_mmu.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/ca988dcdc6683ecd9de5f525ce469588a9141c21
	https://git.kernel.org/stable/c/a2cb8818a3d915cd33a1e8b2babc1bb0c34862c3
	https://git.kernel.org/stable/c/28aa29986dde79e8466bc87569141291053833f5