{"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:\n\nhwrng: core - use RCU and work_struct to fix race condition\n\nCurrently, hwrng_fill is not cleared until the hwrng_fillfn() thread\nexits. 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","slug":"CVE-2026-45949","body":"## Overview\n\nIn the Linux kernel, the following vulnerability has been resolved:\n\nhwrng: core - use RCU and work_struct to fix race condition\n\nCurrently, hwrng_fill is not cleared until the hwrng_fillfn() thread\nexits. Since hwrng_unregister() reads hwrng_fill outside the rng_mutex\nlock, a concurrent hwrng_unregister() may call kthread_stop() again on\nthe same task.\n\nAdditionally, if hwrng_unregister() is called immediately after\nhwrng_register(), the stopped thread may have never been executed. Thus,\nhwrng_fill remains dirty even after hwrng_unregister() returns. In this\ncase, subsequent calls to hwrng_register() will fail to start new\nthreads, and hwrng_unregister() will call kthread_stop() on the same\nfreed task. In both cases, a use-after-free occurs:\n\nrefcount_t: addition on 0; use-after-free.\nWARNING: ... at lib/refcount.c:25 refcount_warn_saturate+0xec/0x1c0\nCall Trace:\n kthread_stop+0x181/0x360\n hwrng_unregister+0x288/0x380\n virtrng_remove+0xe3/0x200\n\nThis patch fixes the race by protecting the global hwrng_fill pointer\ninside the rng_mutex lock, so that hwrng_fillfn() thread is stopped only\nonce, and calls to kthread_run() and kthread_stop() are serialized\nwith the lock held.\n\nTo avoid deadlock in hwrng_fillfn() while being stopped with the lock\nheld, we convert current_rng to RCU, so that get_current_rng() can read\ncurrent_rng without holding the lock. To remove the lock from put_rng(),\nwe also delay the actual cleanup into a work_struct.\n\nSince get_current_rng() no longer returns ERR_PTR values, the IS_ERR()\nchecks are removed from its callers.\n\nWith hwrng_fill protected by the rng_mutex lock, hwrng_fillfn() can no\nlonger clear hwrng_fill itself. Therefore, if hwrng_fillfn() returns\ndirectly after current_rng is dropped, kthread_stop() would be called on\na freed task_struct later. To fix this, hwrng_fillfn() calls schedule()\nnow to keep the task alive until being stopped. The kthread_stop() call\nis also moved from hwrng_unregister() to drop_current_rng(), ensuring\nkthread_stop() is called on all possible paths where current_rng becomes\nNULL, so that the thread would not wait forever.\n\n## Affected\n\n- `Linux >= be4000bc4644d027c519b6361f5ae3bbfc52c347 < 1cde96d5d53b9105b48617afbc4682a83db4ff04`\n- `Linux >= be4000bc4644d027c519b6361f5ae3bbfc52c347 < d5b7730f06994499632026c30e38e0317c4569e2`\n- `Linux >= be4000bc4644d027c519b6361f5ae3bbfc52c347 < dcf416eb88eafe1e3c0f920a14bdffd10bc4d259`\n- `Linux >= be4000bc4644d027c519b6361f5ae3bbfc52c347 < ad38f2cdfef9a2f2899c30cad269baec5bfd4a5d`\n- `Linux >= be4000bc4644d027c519b6361f5ae3bbfc52c347 < cc2f39d6ac48e6e3cb2d6240bc0d6df839dd0828`\n- `Linux 3.17`\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"sunlit","depthScore":3,"depthScoreParts":{"impact":2.8,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}