linux-cve-announce - CVE-2026-23134: slab: fix kmalloc_nolock() context check for PREEMPT

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Message-ID: <2026021437-CVE-2026-23134-22cb@gregkh>
Date: Sat, 14 Feb 2026 16:14:40 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2026-23134: slab: fix kmalloc_nolock() context check for PREEMPT_RT

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

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

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

slab: fix kmalloc_nolock() context check for PREEMPT_RT

On PREEMPT_RT kernels, local_lock becomes a sleeping lock. The current
check in kmalloc_nolock() only verifies we're not in NMI or hard IRQ
context, but misses the case where preemption is disabled.

When a BPF program runs from a tracepoint with preemption disabled
(preempt_count > 0), kmalloc_nolock() proceeds to call
local_lock_irqsave() which attempts to acquire a sleeping lock,
triggering:

  BUG: sleeping function called from invalid context
  in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 6128
  preempt_count: 2, expected: 0

Fix this by checking !preemptible() on PREEMPT_RT, which directly
expresses the constraint that we cannot take a sleeping lock when
preemption is disabled. This encompasses the previous checks for NMI
and hard IRQ contexts while also catching cases where preemption is
disabled.

The Linux kernel CVE team has assigned CVE-2026-23134 to this issue.


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

	Issue introduced in 6.18 with commit af92793e52c3a99b828ed4bdd277fd3e11c18d08 and fixed in 6.18.8 with commit f60ba4a97ae3f94e4818722ed2e4d260bbb17b44
	Issue introduced in 6.18 with commit af92793e52c3a99b828ed4bdd277fd3e11c18d08 and fixed in 6.19 with commit 99a3e3a1cfc93b8fe318c0a3a5cfb01f1d4ad53c

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-2026-23134
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:
	mm/slub.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/f60ba4a97ae3f94e4818722ed2e4d260bbb17b44
	https://git.kernel.org/stable/c/99a3e3a1cfc93b8fe318c0a3a5cfb01f1d4ad53c