6.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Xiubo Li [ Upstream commit ee611a7509554c4ca1f54f6aefe592fb1df7ea70 ] 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 Cc: stable@vger.kernel.org Signed-off-by: Xiubo Li Reviewed-by: Viacheslav Dubeyko Signed-off-by: Ilya Dryomov Signed-off-by: Sasha Levin --- fs/ceph/mds_client.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/fs/ceph/mds_client.c b/fs/ceph/mds_client.c index a2a63ea1f0ac2..342d8778b69cf 100644 --- a/fs/ceph/mds_client.c +++ b/fs/ceph/mds_client.c @@ -5172,9 +5172,11 @@ static void check_new_map(struct ceph_mds_client *mdsc, ceph_mdsmap_get_addr(newmap, i), sizeof(struct ceph_entity_addr))) { /* just close it */ + ceph_get_mds_session(s); mutex_unlock(&mdsc->mutex); mutex_lock(&s->s_mutex); mutex_lock(&mdsc->mutex); + ceph_put_mds_session(s); ceph_con_close(&s->s_con); mutex_unlock(&s->s_mutex); s->s_state = CEPH_MDS_SESSION_RESTARTING; @@ -5187,10 +5189,12 @@ static void check_new_map(struct ceph_mds_client *mdsc, */ if (s->s_state == CEPH_MDS_SESSION_RESTARTING && newstate >= CEPH_MDS_STATE_RECONNECT) { + ceph_get_mds_session(s); mutex_unlock(&mdsc->mutex); clear_bit(i, targets); send_mds_reconnect(mdsc, s); mutex_lock(&mdsc->mutex); + ceph_put_mds_session(s); } /* @@ -5203,9 +5207,11 @@ static void check_new_map(struct ceph_mds_client *mdsc, pr_info_client(cl, "mds%d recovery completed\n", s->s_mds); kick_requests(mdsc, i); + ceph_get_mds_session(s); mutex_unlock(&mdsc->mutex); mutex_lock(&s->s_mutex); mutex_lock(&mdsc->mutex); + ceph_put_mds_session(s); ceph_kick_flushing_caps(mdsc, s); mutex_unlock(&s->s_mutex); wake_up_session_caps(s, RECONNECT); -- 2.53.0