{"id":"CVE-2026-89655","aliases":[],"url":"https://o3.security/vulnerability/CVE-2026-89655","summary":"ceph: fix UAF in __kick_flushing_caps() on cf entry freed during unlock","details":"In the Linux kernel, the following vulnerability has been resolved:\n\nceph: fix UAF in __kick_flushing_caps() on cf entry freed during unlock\n\nlist_for_each_entry() iterates ci->i_cap_flush_list but drops\ni_ceph_lock to send cap messages.  During the unlock window,\nhandle_cap_flush_ack() can acquire i_ceph_lock, detach cf entries\nwith tid <= flush_tid from the list, release i_ceph_lock, and free\nthem via ceph_free_cap_flush() outside any lock.  When the original\nthread reacquires i_ceph_lock and the for-loop macro advances via\ncf = list_next_entry(cf, i_list), it dereferences cf->i_list.next\non freed memory.\n\nThe race timeline:\n\n  __kick_flushing_caps()              handle_cap_flush_ack()\n  -----------------------             -----------------------\n  holds i_ceph_lock        <---\n  iterates to cf (tid=10)\n  prepares FLUSH message\n  drops i_ceph_lock        <---\n  __send_cap() ── FLUSH(tid=10)\n\t                              MDS sends FLUSH_ACK(tid=10)\n                           --->       acquires i_ceph_lock\n                                      cf->tid(10) <= flush_tid(10),\n                                      detaches cf from i_cap_flush_list\n                                      drops i_ceph_lock\n                                      ceph_free_cap_flush(cf) <- frees it!\n  acquires i_ceph_lock     <---\n  for-loop advances:\n    cf = list_next_entry(cf, i_list)\n      -- UAF on freed cf->i_list.next\n\nThe cf was just sent by __kick_flushing_caps itself via __send_cap().\nThe MDS may respond with FLUSH_ACK quickly enough that\nhandle_cap_flush_ack() frees cf before __kick_flushing_caps can\nfinish the iteration.\n\nFix by converting to a manual while loop: save the next pointer\nunder i_ceph_lock before dropping it, then use the saved pointer\nafter reacquiring, so the potentially-freed cf is never accessed again.","published":"2026-09-11T19:45:44.841Z","modified":"2026-09-14T03:46:23.206507396Z","cvss":{"score":9.8,"severity":"CRITICAL","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H"},"epss":null,"cisaKev":null,"exploitsKnown":null,"affectedPackages":[{"ecosystem":"Linux","name":"Kernel","fixedVersion":"6.12.109"}],"fix":null,"references":[{"type":"WEB","url":"https://git.kernel.org/stable/c/2701431aa3cc8b23efe6890182e7b04f5e76fab5"},{"type":"WEB","url":"https://git.kernel.org/stable/c/2dba24dcd5050be4b7b119e6f0b01f62203b5d26"},{"type":"WEB","url":"https://git.kernel.org/stable/c/7af4c4f01305b0935adf6d4301b1ec407025485d"},{"type":"WEB","url":"https://git.kernel.org/stable/c/fe46746087b5b9c5bb2d022df6c7819218494ced"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/89xxx/CVE-2026-89655.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-89655"},{"type":"PACKAGE","url":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-09-14T03:46:23.206507396Z"}}