GHSA-HWG3-WMFR-8Q53
Vulnerability from github – Published: 2026-09-11 21:31 – Updated: 2026-09-13 09:32In the Linux kernel, the following vulnerability has been resolved:
ceph: fix UAF in check_new_map() on session freed during unlock
check_new_map() iterates mdsc->sessions[] and for each active session drops mdsc->mutex to perform per-session operations. The forced-close path (rank removed from map) correctly takes a reference on s via ceph_get_mds_session() before releasing mdsc->mutex, but three other paths do not:
Path A (address changed): mutex_unlock → mutex_lock(&s->s_mutex) Path B (reconnect): mutex_unlock → send_mds_reconnect(mdsc, s) Path C (active transition): mutex_unlock → mutex_lock(&s->s_mutex)
Without the extra reference, another thread can acquire mdsc->mutex during the unlock window, call __unregister_session() which drops the last reference on s, and free it. The original thread then accesses freed memory via s->s_mutex.
Fix by adding ceph_get_mds_session(s) before each mutex_unlock and ceph_put_mds_session(s) after the corresponding mutex_lock, matching the pattern already used in the forced-close path.
Race timeline (Path A):
Thread A (check_new_map) Thread B (another map update holds mdsc->mutex or session teardown) -------------------------- -------------------------- s = mdsc->sessions[i] (refcount == 1, held only by sessions[] array)
mutex_unlock(&mdsc->mutex) ---> acquires mdsc->mutex __unregister_session(mdsc, s) sessions[i] = NULL ceph_put_mds_session(s) refcount: 1 -> 0 kfree(s) <--- freed!
mutex_lock(&s->s_mutex) UAF on freed s->s_mutex
{
"affected": [],
"aliases": [
"CVE-2026-89654"
],
"database_specific": {
"cwe_ids": [],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-09-11T20:19:51Z",
"severity": "CRITICAL"
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\nceph: fix UAF in check_new_map() on session freed during unlock\n\ncheck_new_map() iterates mdsc-\u003esessions[] and for each active session\ndrops mdsc-\u003emutex to perform per-session operations. The forced-close\npath (rank removed from map) correctly takes a reference on s via\nceph_get_mds_session() before releasing mdsc-\u003emutex, but three other\npaths do not:\n\n Path A (address changed): mutex_unlock \u2192 mutex_lock(\u0026s-\u003es_mutex)\n Path B (reconnect): mutex_unlock \u2192 send_mds_reconnect(mdsc, s)\n Path C (active transition): mutex_unlock \u2192 mutex_lock(\u0026s-\u003es_mutex)\n\nWithout the extra reference, another thread can acquire mdsc-\u003emutex\nduring the unlock window, call __unregister_session() which drops the\nlast reference on s, and free it. The original thread then accesses\nfreed memory via s-\u003es_mutex.\n\nFix by adding ceph_get_mds_session(s) before each mutex_unlock and\nceph_put_mds_session(s) after the corresponding mutex_lock, matching\nthe pattern already used in the forced-close path.\n\nRace timeline (Path A):\n\n Thread A (check_new_map) Thread B (another map update\n holds mdsc-\u003emutex or session teardown)\n -------------------------- --------------------------\n s = mdsc-\u003esessions[i]\n (refcount == 1, held only by\n sessions[] array)\n\n mutex_unlock(\u0026mdsc-\u003emutex)\n ---\u003e acquires mdsc-\u003emutex\n __unregister_session(mdsc, s)\n sessions[i] = NULL\n ceph_put_mds_session(s)\n refcount: 1 -\u003e 0\n kfree(s) \u003c--- freed!\n\n mutex_lock(\u0026s-\u003es_mutex)\n UAF on freed s-\u003es_mutex",
"id": "GHSA-hwg3-wmfr-8q53",
"modified": "2026-09-13T09:32:26Z",
"published": "2026-09-11T21:31:35Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-89654"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/21d5be092d947f8d83f76f7ebf3989e7e9230a98"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/ee611a7509554c4ca1f54f6aefe592fb1df7ea70"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
"type": "CVSS_V3"
}
]
}
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