Linux Kernel fprobe Use-After-Free via RCU Misuse
CVE-2026-98861 Published on October 18, 2026
fprobe: Use guard(rcu_sched_notrace) and check rcu_is_watching()
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.
Products Associated with CVE-2026-98861
Want to know whenever a new CVE is published for Linux Kernel? stack.watch will email you.
Affected Versions
Linux:- Version 56b4cfcf1518245493c60fd39c56978f508f1816 and below a85d0f00671b4d4527317c10ba018680f7d8d673 is affected.
- Version 657b594b2084b39a4bc6d8493aa2140cb00cea49 and below dd4a0d4993633b45470abf6da4ea0ca563402245 is affected.
- Version 657b594b2084b39a4bc6d8493aa2140cb00cea49 and below e0a6249190402a28f1e2925a81acf573157d55ef is affected.
- Version a4f6a9005ed6cfd360ef2520430927f05f92ffb0 is affected.
- Version 6.18.34 and below 6.18.56 is affected.
- Version 7.0.11 and below 7.1 is affected.
- Version 7.1 is affected.
- Before 7.1 is unaffected.
- Version 6.18.56, <= 6.18.* is unaffected.
- Version 7.2.10, <= 7.2.* is unaffected.
- Version 7.3-rc6, <= * is unaffected.