{"id":"CVE-2026-46242","summary":"eventpoll: fix ep_remove struct eventpoll / struct file UAF","details":"In the Linux kernel, the following vulnerability has been resolved:\n\neventpoll: fix ep_remove struct eventpoll / struct file UAF\n\nep_remove() (via ep_remove_file()) cleared file-\u003ef_ep under\nfile-\u003ef_lock but then kept using @file inside the critical section\n(is_file_epoll(), hlist_del_rcu() through the head, spin_unlock).\nA concurrent __fput() taking the eventpoll_release() fastpath in\nthat window observed the transient NULL, skipped\neventpoll_release_file() and ran to f_op-\u003erelease / file_free().\n\nFor the epoll-watches-epoll case, f_op-\u003erelease is\nep_eventpoll_release() -\u003e ep_clear_and_put() -\u003e ep_free(), which\nkfree()s the watched struct eventpoll. Its embedded -\u003erefs\nhlist_head is exactly where epi-\u003efllink.pprev points, so the\nsubsequent hlist_del_rcu()'s \"*pprev = next\" scribbles into freed\nkmalloc-192 memory.\n\nIn addition, struct file is SLAB_TYPESAFE_BY_RCU, so the slot\nbacking @file could be recycled by alloc_empty_file() --\nreinitializing f_lock and f_ep -- while ep_remove() is still\nnominally inside that lock. The upshot is an attacker-controllable\nkmem_cache_free() against the wrong slab cache.\n\nPin @file via epi_fget() at the top of ep_remove() and gate the\ncritical section on the pin succeeding. With the pin held @file\ncannot reach refcount zero, which holds __fput() off and\ntransitively keeps the watched struct eventpoll alive across the\nhlist_del_rcu() and the f_lock use, closing both UAFs.\n\nIf the pin fails @file has already reached refcount zero and its\n__fput() is in flight. Because we bailed before clearing f_ep,\nthat path takes the eventpoll_release() slow path into\neventpoll_release_file() and blocks on ep-\u003emtx until the waiter\nside's ep_clear_and_put() drops it. The bailed epi's share of\nep-\u003erefcount stays intact, so the trailing ep_refcount_dec_and_test()\nin ep_clear_and_put() cannot free the eventpoll out from under\neventpoll_release_file(); the orphaned epi is then cleaned up\nthere.\n\nA successful pin also proves we are not racing\neventpoll_release_file() on this epi, so drop the now-redundant\nre-check of epi-\u003edying under f_lock. The cheap lockless\nREAD_ONCE(epi-\u003edying) fast-path bailout stays.","modified":"2026-06-05T18:29:22.630167694Z","published":"2026-05-30T12:13:45.594Z","related":["openSUSE-SU-2026:10954-1"],"database_specific":{"cna_assigner":"Linux","osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/46xxx/CVE-2026-46242.json"},"references":[{"type":"WEB","url":"https://git.kernel.org/stable/c/a6dc643c69311677c574a0f17a3f4d66a5f3744b"},{"type":"WEB","url":"https://git.kernel.org/stable/c/ced39b6a8062bac5c18a1c3df85634107eb8664a"},{"type":"WEB","url":"https://git.kernel.org/stable/c/ef4ca02e95363e78977ca04340d44fe3b4b2b81f"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/46xxx/CVE-2026-46242.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-46242"},{"type":"PACKAGE","url":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"58c9b016e12855286370dfb704c08498edbc857a"},{"fixed":"ef4ca02e95363e78977ca04340d44fe3b4b2b81f"},{"fixed":"ced39b6a8062bac5c18a1c3df85634107eb8664a"},{"fixed":"a6dc643c69311677c574a0f17a3f4d66a5f3744b"}]}],"database_specific":{"source":"https://storage.googleapis.com/osv-test-cve-osv-conversion/osv-output/CVE-2026-46242.json"}},{"package":{"name":"Kernel","ecosystem":"Linux"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"6.4.0"},{"fixed":"6.18.33"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.19.0"},{"fixed":"7.0.10"}]}],"database_specific":{"source":"https://storage.googleapis.com/osv-test-cve-osv-conversion/osv-output/CVE-2026-46242.json"}}],"schema_version":"1.7.5"}