CVE-2026-46242
- Source
- https://cve.org/CVERecord?id=CVE-2026-46242
- Import Source
- https://storage.googleapis.com/osv-test-cve-osv-conversion/osv-output/CVE-2026-46242.json
- JSON Data
- https://api.test.osv.dev/v1/vulns/CVE-2026-46242
- Downstream
- Related
- Published
- 2026-05-30T12:13:45Z
- Modified
- 2026-09-04T18:26:39Z
- Summary
- eventpoll: fix ep_remove struct eventpoll / struct file UAF
- Details
-
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.
- Database specific
{ "cna_assigner": "Linux", "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/46xxx/CVE-2026-46242.json" }- References
-
- https://git.kernel.org/stable/c/a6dc643c69311677c574a0f17a3f4d66a5f3744b
- https://git.kernel.org/stable/c/ced39b6a8062bac5c18a1c3df85634107eb8664a
- https://git.kernel.org/stable/c/ef4ca02e95363e78977ca04340d44fe3b4b2b81f
- https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/46xxx/CVE-2026-46242.json
- https://nvd.nist.gov/vuln/detail/CVE-2026-46242
- https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git