---
id: CVE-2026-98861
title: 'fprobe: Use guard(rcu_sched_notrace) and check rcu_is_watching()'
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  fprobe: Use guard(rcu_sched_notrace) and check rcu_is_watching()

  unregister_fprobe() and unregister_fprobe_async() (used by BPF
  kprobe-multi) rely on standard RCU grac…
severity: none
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= 56b4cfcf1518245493c60fd39c56978f508f1816 <
    a85d0f00671b4d4527317c10ba018680f7d8d673
  - >-
    Linux >= 657b594b2084b39a4bc6d8493aa2140cb00cea49 <
    dd4a0d4993633b45470abf6da4ea0ca563402245
  - >-
    Linux >= 657b594b2084b39a4bc6d8493aa2140cb00cea49 <
    e0a6249190402a28f1e2925a81acf573157d55ef
  - Linux a4f6a9005ed6cfd360ef2520430927f05f92ffb0
  - Linux >= 6.18.34 < 6.18.56
  - Linux >= 7.0.11 < 7.1
  - Linux 7.1
published: '2026-10-18'
updated: '2026-10-18'
sourceUpdated: '2026-10-18T15:51:22.271Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-98861'
references:
  - url: 'https://git.kernel.org/stable/c/a85d0f00671b4d4527317c10ba018680f7d8d673'
  - url: 'https://git.kernel.org/stable/c/dd4a0d4993633b45470abf6da4ea0ca563402245'
  - url: 'https://git.kernel.org/stable/c/e0a6249190402a28f1e2925a81acf573157d55ef'
tags:
  - cve.org
ingestedAt: '2026-10-18T16:47:32.459Z'
---

## Overview

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

fprobe: Use guard(rcu_sched_notrace) and check rcu_is_watching()

unregister_fprobe() and unregister_fprobe_async() (used by BPF
kprobe-multi) rely on standard RCU grace periods (synchronize_rcu()
and call_rcu()) to wait until in-flight fprobe handlers complete before
freeing the fprobe.

However, if an fprobe handler executes while RCU is not watching (such
as in the idle loop or nohz_full extended quiescent states), standard
RCU does not track preemption-disabled sections. Consequently,
synchronize_rcu() does not wait for those executions, which can lead
to a use-after-free if the fprobe is freed immediately after
unregistration. Ensure handlers exit early when !rcu_is_watching().

Furthermore, fprobe_fgraph_entry() and fprobe_ftrace_entry() previously
used guard(rcu)() and rcu_read_lock(), which invoke lockdep on every
hit under CONFIG_PROVE_LOCKING. This adds overhead and can cause lockdep
recursion if probed functions interact with lockdep.

Since rhltable_lookup() and rhl_for_each_entry_rcu() use
rcu_dereference_all_check() (which checks rcu_read_lock_any_held()),
holding preemption disabled via rcu_read_lock_sched_notrace() is fully
valid and sufficient so long as rcu_is_watching() is true.

Define and use guard(rcu_sched_notrace)() across fprobe_ftrace_entry(),
fprobe_fgraph_entry(), and fprobe_return(). This eliminates fast-path
rcu_read_lock() and lockdep overhead while guaranteeing safe grace
period synchronization.

## Affected

- `Linux >= 56b4cfcf1518245493c60fd39c56978f508f1816 < a85d0f00671b4d4527317c10ba018680f7d8d673`
- `Linux >= 657b594b2084b39a4bc6d8493aa2140cb00cea49 < dd4a0d4993633b45470abf6da4ea0ca563402245`
- `Linux >= 657b594b2084b39a4bc6d8493aa2140cb00cea49 < e0a6249190402a28f1e2925a81acf573157d55ef`
- `Linux a4f6a9005ed6cfd360ef2520430927f05f92ffb0`
- `Linux >= 6.18.34 < 6.18.56`
- `Linux >= 7.0.11 < 7.1`
- `Linux 7.1`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.