{"id":"CVE-2026-89791","summary":"perf: Fix use-after-free when perf mmap() revival races with the last munmap()","details":"In the Linux kernel, the following vulnerability has been resolved:\n\nperf: Fix use-after-free when perf mmap() revival races with the last munmap()\n\nperf_mmap_close() drops rb-\u003emmap_count *without* holding\nevent-\u003emmap_mutex (the refcount_dec_and_test() right before the\nrefcount_dec_and_mutex_lock() of event-\u003emmap_count). A concurrent\nperf_mmap_rb() can slot its entire \"revival\" path into that window\n(perf_mmap holds event-\u003emmap_mutex for its whole duration, including\nrb_alloc):\n\n  munmap side (perf_mmap_close)          mmap side (perf_mmap_rb)\n  -----------------------------------    --------------------------------\n  rb-\u003emmap_count 1 -\u003e 0   (no lock)      (holds event-\u003emmap_mutex)\n                                         inc_not_zero(rb-\u003emmap_count) fails\n                                         ring_buffer_attach(event, NULL)\n                                         rb_alloc() + attach new rb\n                                         refcount_set(&event-\u003emmap_count, 1)\n  lock; event-\u003emmap_count 1 -\u003e 0\n  ring_buffer_attach(event, NULL)\n  ring_buffer_put() -\u003e frees the *new* rb\n\nThe revival's refcount_set(&event-\u003emmap_count, 1) is an invisible\n1 -\u003e 1 write: the close frees the just-revived buffer although the\nother process still has it mapped -- a page-level use-after-free\nallowing local privilege escalation to root by any unprivileged user\n(default kernel.perf_event_paranoid=2).\n\nSwap the order of the two counter updates: event-\u003emmap_count is\ndropped first via refcount_dec_and_mutex_lock(), so its 1 -\u003e 0\ntransition and the ring_buffer_attach() stay serialized with\nperf_mmap(). rb-\u003emmap_count == 0 then implies every event using the\nbuffer is detached already, so the result of the rb-\u003emmap_count drop\ncan gate the remaining teardown directly and detach_rest is no longer\nneeded.\n\nAn earlier fix for this race from Kyle Zeng and David Lee takes\nevent-\u003emmap_mutex around both counter updates [0]; here the not-last\nclose stays lockless.","modified":"2026-09-17T03:47:26.588352600Z","published":"2026-09-16T08:48:27.020Z","database_specific":{"cna_assigner":"Linux","osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/89xxx/CVE-2026-89791.json"},"references":[{"type":"PACKAGE","url":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"},{"type":"WEB","url":"https://git.kernel.org/stable/c/0c739f54f1c77f3a4643160cd2e031b6c2f2aab6"},{"type":"WEB","url":"https://git.kernel.org/stable/c/58a8108bc73de0740d5b88150465d6690ea5f85f"},{"type":"WEB","url":"https://git.kernel.org/stable/c/929cb3b9dc818dd9fa89d510d4ff2b255e42badd"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/89xxx/CVE-2026-89791.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-89791"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"59741451b49ce9964a9758c19d6f7df2a1255c75"},{"fixed":"929cb3b9dc818dd9fa89d510d4ff2b255e42badd"},{"fixed":"0c739f54f1c77f3a4643160cd2e031b6c2f2aab6"},{"fixed":"58a8108bc73de0740d5b88150465d6690ea5f85f"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-89791.json"}},{"package":{"name":"Kernel","ecosystem":"Linux"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"6.18.0"},{"fixed":"6.18.52"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.19.0"},{"fixed":"7.2.5"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-89791.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H"}]}