Race Condition Affecting kernel-rt-64k-devel-matched package, versions *
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Test your applications- Snyk IDSNYK-CENTOS9-KERNELRT64KDEVELMATCHED-16991078
- published28 May 2026
- disclosed27 May 2026
Introduced: 27 May 2026
NewCVE-2026-45949 (opens in a new tab)How to fix?
There is no fixed version for Centos:9 kernel-rt-64k-devel-matched.
NVD Description
Note: Versions mentioned in the description apply only to the upstream kernel-rt-64k-devel-matched package and not the kernel-rt-64k-devel-matched package as distributed by Centos.
See How to fix? for Centos:9 relevant fixed versions and status.
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.
References
- https://access.redhat.com/security/cve/CVE-2026-45949
- https://git.kernel.org/stable/c/ad38f2cdfef9a2f2899c30cad269baec5bfd4a5d
- https://git.kernel.org/stable/c/cc2f39d6ac48e6e3cb2d6240bc0d6df839dd0828
- https://git.kernel.org/stable/c/d5b7730f06994499632026c30e38e0317c4569e2
- https://git.kernel.org/stable/c/dcf416eb88eafe1e3c0f920a14bdffd10bc4d259