CVE-2026-46242
摘要
In the Linux kernel, the following vulnerability has been resolved:eventpoll: fix ep_remove struct eventpoll / struct file UAFep_remove() (via ep_remove_file()) cleared file->f_ep underfile->f_lock but then kept using @file inside the critical section(is_file_epoll(), hlist_del_rcu() through the head, spin_unlock).A concurrent __fput() taking the eventpoll_release() fastpath inthat window observed the transient NULL, skippedeventpoll_release_file() and ran to f_op->release / file_free().For the epoll-watches-epoll case, f_op->release isep_eventpoll_release() -> ep_clear_and_put() -> ep_free(), whichkfree()s the watched struct eventpoll. Its embedded ->refshlist_head is exactly where epi->fllink.pprev points, so thesubsequent hlist_del_rcu()'s "*pprev = next" scribbles into freedkmalloc-192 memory.In addition, struct file is SLAB_TYPESAFE_BY_RCU, so the slotbacking @file could be recycled by alloc_empty_file() --reinitializing f_lock and f_ep -- while ep_remove() is stillnominally inside that lock. The upshot is an attacker-controllablekmem_cache_free() against the wrong slab cache.Pin @file via epi_fget() at the top of ep_remove() and gate thecritical section on the pin succeeding. With the pin held @filecannot reach refcount zero, which holds __fput() off andtransitively keeps the watched struct eventpoll alive across thehlist_del_rcu() and the f_lock use, closing both UAFs.If the pin fails @file has already reached refcount zero and its__fput() is in flight. Because we bailed before clearing f_ep,that path takes the eventpoll_release() slow path intoeventpoll_release_file() and blocks on ep->mtx until the waiterside's ep_clear_and_put() drops it. The bailed epi's share ofep->refcount stays intact, so the trailing ep_refcount_dec_and_test()in ep_clear_and_put() cannot free the eventpoll out from undereventpoll_release_file(); the orphaned epi is then cleaned upthere.A successful pin also proves we are not racingeventpoll_release_file() on this epi, so drop the now-redundantre-check of epi->dying under f_lock. The cheap locklessREAD_ONCE(epi->dying) fast-path bailout stays.
标签
- cve:cve-2026-46242
- type:cve
- vendor:alibaba
扩展字段
{
"cve_id": "CVE-2026-46242",
"raw_pub_date": "Fri, 24 Jul 2026 17:46:40 +0800"
}