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CVE PROGRAM SOURCE RECORD7.8 High

CVE-2026-46242

eventpoll: fix ep_remove struct eventpoll / struct file UAF

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Status
Published
Published
Updated
Assigning organization
Linux

Description

In the Linux kernel, the following vulnerability has been resolved: eventpoll: fix ep_remove struct eventpoll / struct file UAF ep_remove() (via ep_remove_file()) cleared file->f_ep under file->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 in that window observed the transient NULL, skipped eventpoll_release_file() and ran to f_op->release / file_free(). For the epoll-watches-epoll case, f_op->release is ep_eventpoll_release() -> ep_clear_and_put() -> ep_free(), which kfree()s the watched struct eventpoll. Its embedded ->refs hlist_head is exactly where epi->fllink.pprev points, so the subsequent hlist_del_rcu()'s "*pprev = next" scribbles into freed kmalloc-192 memory. In addition, struct file is SLAB_TYPESAFE_BY_RCU, so the slot backing @file could be recycled by alloc_empty_file() -- reinitializing f_lock and f_ep -- while ep_remove() is still nominally inside that lock. The upshot is an attacker-controllable kmem_cache_free() against the wrong slab cache. Pin @file via epi_fget() at the top of ep_remove() and gate the critical section on the pin succeeding. With the pin held @file cannot reach refcount zero, which holds __fput() off and transitively keeps the watched struct eventpoll alive across the hlist_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 into eventpoll_release_file() and blocks on ep->mtx until the waiter side's ep_clear_and_put() drops it. The bailed epi's share of ep->refcount stays intact, so the trailing ep_refcount_dec_and_test() in ep_clear_and_put() cannot free the eventpoll out from under eventpoll_release_file(); the orphaned epi is then cleaned up there. A successful pin also proves we are not racing eventpoll_release_file() on this epi, so drop the now-redundant re-check of epi->dying under f_lock. The cheap lockless READ_ONCE(epi->dying) fast-path bailout stays.

Affected products

Version statuses are supplied by the assigning organization. Consult the original record for detailed ranges and platform conditions.

Linux Linux

Default version status: unaffected

  • f2451def095c1743adcfcb0cb5dadc86034e162a to < a10fbbe74e1c743beb1bb312109366667461df8aaffected
  • a1f93804449d13f97dabd4b996817de4bf1ed67a to < 3e1144d2515d28e4312e663ea05eac203101491daffected
  • 58c9b016e12855286370dfb704c08498edbc857a to < 2de4db145b2992da496fea6c51f9839be678ae24affected
  • 58c9b016e12855286370dfb704c08498edbc857a to < 9324de74a3a59b9fde9b62ee45ebaa71458ba2e5affected
  • 58c9b016e12855286370dfb704c08498edbc857a to < ef4ca02e95363e78977ca04340d44fe3b4b2b81faffected
  • 58c9b016e12855286370dfb704c08498edbc857a to < ced39b6a8062bac5c18a1c3df85634107eb8664aaffected
  • 58c9b016e12855286370dfb704c08498edbc857a to < a6dc643c69311677c574a0f17a3f4d66a5f3744baffected
  • 5.15.209 to < 5.15.222affected
  • 6.1.175 to < 6.1.178affected

Linux Linux

Default version status: affected

  • 6.4affected
  • 0 to < 6.4unaffected
  • 5.15.222 to ≤ 5.15.*unaffected
  • 6.1.178 to ≤ 6.1.*unaffected
  • 6.6.144 to ≤ 6.6.*unaffected
  • 6.12.95 to ≤ 6.12.*unaffected
  • 6.18.33 to ≤ 6.18.*unaffected
  • 7.0.10 to ≤ 7.0.*unaffected
  • 7.1 to ≤ *unaffected

References