---
id: CVE-2026-45949
title: 'hwrng: core - use RCU and work_struct to fix race condition'
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  hwrng: core - use RCU and work_struct to fix race condition

  Currently, hwrng_fill is not cleared until the hwrng_fillfn() thread
  exits. Since hwrng_unregister() reads …
severity: none
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= be4000bc4644d027c519b6361f5ae3bbfc52c347 <
    1cde96d5d53b9105b48617afbc4682a83db4ff04
  - >-
    Linux >= be4000bc4644d027c519b6361f5ae3bbfc52c347 <
    d5b7730f06994499632026c30e38e0317c4569e2
  - >-
    Linux >= be4000bc4644d027c519b6361f5ae3bbfc52c347 <
    dcf416eb88eafe1e3c0f920a14bdffd10bc4d259
  - >-
    Linux >= be4000bc4644d027c519b6361f5ae3bbfc52c347 <
    ad38f2cdfef9a2f2899c30cad269baec5bfd4a5d
  - >-
    Linux >= be4000bc4644d027c519b6361f5ae3bbfc52c347 <
    cc2f39d6ac48e6e3cb2d6240bc0d6df839dd0828
  - Linux 3.17
published: '2026-05-27'
updated: '2026-10-21'
sourceUpdated: '2026-10-21T12:41:05.248Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-45949'
references:
  - url: 'https://git.kernel.org/stable/c/1cde96d5d53b9105b48617afbc4682a83db4ff04'
  - url: 'https://git.kernel.org/stable/c/d5b7730f06994499632026c30e38e0317c4569e2'
  - url: 'https://git.kernel.org/stable/c/dcf416eb88eafe1e3c0f920a14bdffd10bc4d259'
  - url: 'https://git.kernel.org/stable/c/ad38f2cdfef9a2f2899c30cad269baec5bfd4a5d'
  - url: 'https://git.kernel.org/stable/c/cc2f39d6ac48e6e3cb2d6240bc0d6df839dd0828'
tags:
  - cve.org
epss: 0.00107
epssPercentile: 0.01113
ingestedAt: '2026-10-21T12:48:53.633Z'
---

## Overview

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

hwrng: core - use RCU and work_struct to fix race condition

Currently, hwrng_fill is not cleared until the hwrng_fillfn() thread
exits. Since hwrng_unregister() reads hwrng_fill outside the rng_mutex
lock, a concurrent hwrng_unregister() may call kthread_stop() again on
the same task.

Additionally, if hwrng_unregister() is called immediately after
hwrng_register(), the stopped thread may have never been executed. Thus,
hwrng_fill remains dirty even after hwrng_unregister() returns. In this
case, subsequent calls to hwrng_register() will fail to start new
threads, and hwrng_unregister() will call kthread_stop() on the same
freed task. In both cases, a use-after-free occurs:

refcount_t: addition on 0; use-after-free.
WARNING: ... at lib/refcount.c:25 refcount_warn_saturate+0xec/0x1c0
Call Trace:
 kthread_stop+0x181/0x360
 hwrng_unregister+0x288/0x380
 virtrng_remove+0xe3/0x200

This patch fixes the race by protecting the global hwrng_fill pointer
inside the rng_mutex lock, so that hwrng_fillfn() thread is stopped only
once, and calls to kthread_run() and kthread_stop() are serialized
with the lock held.

To avoid deadlock in hwrng_fillfn() while being stopped with the lock
held, we convert current_rng to RCU, so that get_current_rng() can read
current_rng without holding the lock. To remove the lock from put_rng(),
we also delay the actual cleanup into a work_struct.

Since get_current_rng() no longer returns ERR_PTR values, the IS_ERR()
checks are removed from its callers.

With hwrng_fill protected by the rng_mutex lock, hwrng_fillfn() can no
longer clear hwrng_fill itself. Therefore, if hwrng_fillfn() returns
directly after current_rng is dropped, kthread_stop() would be called on
a freed task_struct later. To fix this, hwrng_fillfn() calls schedule()
now to keep the task alive until being stopped. The kthread_stop() call
is also moved from hwrng_unregister() to drop_current_rng(), ensuring
kthread_stop() is called on all possible paths where current_rng becomes
NULL, so that the thread would not wait forever.

## Affected

- `Linux >= be4000bc4644d027c519b6361f5ae3bbfc52c347 < 1cde96d5d53b9105b48617afbc4682a83db4ff04`
- `Linux >= be4000bc4644d027c519b6361f5ae3bbfc52c347 < d5b7730f06994499632026c30e38e0317c4569e2`
- `Linux >= be4000bc4644d027c519b6361f5ae3bbfc52c347 < dcf416eb88eafe1e3c0f920a14bdffd10bc4d259`
- `Linux >= be4000bc4644d027c519b6361f5ae3bbfc52c347 < ad38f2cdfef9a2f2899c30cad269baec5bfd4a5d`
- `Linux >= be4000bc4644d027c519b6361f5ae3bbfc52c347 < cc2f39d6ac48e6e3cb2d6240bc0d6df839dd0828`
- `Linux 3.17`

## Remediation

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