{"id":"CVE-2026-45949","state":"PUBLISHED","title":"hwrng: core - use RCU and work_struct to fix race condition","description":"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 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.","publishedAt":"2026-05-27T12:18:05.718Z","updatedAt":"2026-10-30T12:25:49.889Z","severity":null,"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"be4000bc4644d027c519b6361f5ae3bbfc52c347","status":"affected","lessThan":"d60bd663b746f17fc01fdc44dd01642594176344","versionType":"git"},{"version":"be4000bc4644d027c519b6361f5ae3bbfc52c347","status":"affected","lessThan":"1cde96d5d53b9105b48617afbc4682a83db4ff04","versionType":"git"},{"version":"be4000bc4644d027c519b6361f5ae3bbfc52c347","status":"affected","lessThan":"d5b7730f06994499632026c30e38e0317c4569e2","versionType":"git"},{"version":"be4000bc4644d027c519b6361f5ae3bbfc52c347","status":"affected","lessThan":"dcf416eb88eafe1e3c0f920a14bdffd10bc4d259","versionType":"git"},{"version":"be4000bc4644d027c519b6361f5ae3bbfc52c347","status":"affected","lessThan":"ad38f2cdfef9a2f2899c30cad269baec5bfd4a5d","versionType":"git"},{"version":"be4000bc4644d027c519b6361f5ae3bbfc52c347","status":"affected","lessThan":"cc2f39d6ac48e6e3cb2d6240bc0d6df839dd0828","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["drivers/char/hw_random/core.c","include/linux/hw_random.h"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"3.17","status":"affected"},{"version":"0","status":"unaffected","lessThan":"3.17","versionType":"semver"},{"version":"6.1.191","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.160","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.75","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.14","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"6.19.4","status":"unaffected","lessThanOrEqual":"6.19.*","versionType":"semver"},{"version":"7.0","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["drivers/char/hw_random/core.c","include/linux/hw_random.h"]}],"references":["https://git.kernel.org/stable/c/d60bd663b746f17fc01fdc44dd01642594176344","https://git.kernel.org/stable/c/1cde96d5d53b9105b48617afbc4682a83db4ff04","https://git.kernel.org/stable/c/d5b7730f06994499632026c30e38e0317c4569e2","https://git.kernel.org/stable/c/dcf416eb88eafe1e3c0f920a14bdffd10bc4d259","https://git.kernel.org/stable/c/ad38f2cdfef9a2f2899c30cad269baec5bfd4a5d","https://git.kernel.org/stable/c/cc2f39d6ac48e6e3cb2d6240bc0d6df839dd0828"],"weaknesses":[],"ingestedAt":"2026-10-30T12:42:04.495Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/45xxx/CVE-2026-45949.json","commit":"db8103c5921aac81d5d90efcf3745980dafabf49","baselineCommit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-45949","state":"PUBLISHED","datePublished":"2026-05-27T12:18:05.718Z","dateUpdated":"2026-10-30T12:25:49.889Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-05-13T15:03:33.088Z"},"containers":{"cna":{"title":"hwrng: core - use RCU and work_struct to fix race condition","descriptions":[{"lang":"en","value":"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 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."}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"be4000bc4644d027c519b6361f5ae3bbfc52c347","status":"affected","lessThan":"d60bd663b746f17fc01fdc44dd01642594176344","versionType":"git"},{"version":"be4000bc4644d027c519b6361f5ae3bbfc52c347","status":"affected","lessThan":"1cde96d5d53b9105b48617afbc4682a83db4ff04","versionType":"git"},{"version":"be4000bc4644d027c519b6361f5ae3bbfc52c347","status":"affected","lessThan":"d5b7730f06994499632026c30e38e0317c4569e2","versionType":"git"},{"version":"be4000bc4644d027c519b6361f5ae3bbfc52c347","status":"affected","lessThan":"dcf416eb88eafe1e3c0f920a14bdffd10bc4d259","versionType":"git"},{"version":"be4000bc4644d027c519b6361f5ae3bbfc52c347","status":"affected","lessThan":"ad38f2cdfef9a2f2899c30cad269baec5bfd4a5d","versionType":"git"},{"version":"be4000bc4644d027c519b6361f5ae3bbfc52c347","status":"affected","lessThan":"cc2f39d6ac48e6e3cb2d6240bc0d6df839dd0828","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["drivers/char/hw_random/core.c","include/linux/hw_random.h"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"3.17","status":"affected"},{"version":"0","status":"unaffected","lessThan":"3.17","versionType":"semver"},{"version":"6.1.191","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.160","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.75","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.14","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"6.19.4","status":"unaffected","lessThanOrEqual":"6.19.*","versionType":"semver"},{"version":"7.0","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["drivers/char/hw_random/core.c","include/linux/hw_random.h"]}],"references":[{"url":"https://git.kernel.org/stable/c/d60bd663b746f17fc01fdc44dd01642594176344"},{"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"}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-10-30T12:25:49.889Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.17","versionEndExcluding":"6.1.191"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.17","versionEndExcluding":"6.6.160"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.17","versionEndExcluding":"6.12.75"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.17","versionEndExcluding":"6.18.14"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.17","versionEndExcluding":"6.19.4"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.17","versionEndExcluding":"7.0"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}}}}}