CVE-2026-64073: irq_work: Fix use-after-free in irq_work_single() on PREEMPT_RT

From: Greg Kroah-Hartman <[email protected]>

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

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

irq_work: Fix use-after-free in irq_work_single() on PREEMPT_RT

On PREEMPT_RT, non-HARD irq_work runs in per-CPU kthreads via
run_irq_workd(), so irq_work_sync() uses rcuwait() to wait for BUSY==0.

After irq_work_single() clears BUSY via atomic_cmpxchg(), it still
dereferences @work for irq_work_is_hard() and rcuwait_wake_up().

An irq_work_sync() caller on another CPU that enters after BUSY is cleared
can observe BUSY==0 immediately, return, and free the work before those
accesses complete — causing a use-after-free.

Fix this by wrapping run_irq_workd() in guard(rcu)() so that the entire
irq_work_single() execution is within an RCU read-side critical
section. Then add synchronize_rcu() in irq_work_sync() after
rcuwait_wait_event() to ensure the caller waits for the RCU grace period
before returning, preventing premature frees.

The Linux kernel CVE team has assigned CVE-2026-64073 to this issue.


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

	Issue introduced in 5.16 with commit 810979682ccc98dbd83f341c18a2e556c30a7164 and fixed in 6.1.175 with commit 2dc79362302922cb18f35e262712b5e58de65442
	Issue introduced in 5.16 with commit 810979682ccc98dbd83f341c18a2e556c30a7164 and fixed in 6.6.142 with commit eef4f71b46a9929ac33e968538c9dd5d96a02460
	Issue introduced in 5.16 with commit 810979682ccc98dbd83f341c18a2e556c30a7164 and fixed in 6.12.92 with commit 684a78183c54c23e70d1cba320f7fc184604210b
	Issue introduced in 5.16 with commit 810979682ccc98dbd83f341c18a2e556c30a7164 and fixed in 6.18.34 with commit 18c0456ea2615b1a743a6db739c74411c3b42bc6
	Issue introduced in 5.16 with commit 810979682ccc98dbd83f341c18a2e556c30a7164 and fixed in 7.0.11 with commit 81b582784518196eff1050212a046bc29d3a05dd
	Issue introduced in 5.16 with commit 810979682ccc98dbd83f341c18a2e556c30a7164 and fixed in 7.1 with commit 91840be8f710370607f949a627e070896faeddb8

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-2026-64073
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/irq_work.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/2dc79362302922cb18f35e262712b5e58de65442
	https://git.kernel.org/stable/c/eef4f71b46a9929ac33e968538c9dd5d96a02460
	https://git.kernel.org/stable/c/684a78183c54c23e70d1cba320f7fc184604210b
	https://git.kernel.org/stable/c/18c0456ea2615b1a743a6db739c74411c3b42bc6
	https://git.kernel.org/stable/c/81b582784518196eff1050212a046bc29d3a05dd
	https://git.kernel.org/stable/c/91840be8f710370607f949a627e070896faeddb8