From ee611a7509554c4ca1f54f6aefe592fb1df7ea70 Mon Sep 17 00:00:00 2001 From: Xiubo Li Date: Tue, 14 Jul 2026 16:13:44 +0800 Subject: [PATCH] ceph: fix UAF in check_new_map() on session freed during unlock MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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 --- 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 4c38fe5a9a4b..d11c7eeaf0bf 100644 --- a/fs/ceph/mds_client.c +++ b/fs/ceph/mds_client.c @@ -5890,9 +5890,11 @@ 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; @@ -5907,6 +5909,7 @@ static void check_new_map(struct ceph_mds_client *mdsc, newstate >= CEPH_MDS_STATE_RECONNECT) { int rc; + ceph_get_mds_session(s); mutex_unlock(&mdsc->mutex); clear_bit(i, targets); rc = send_mds_reconnect(mdsc, s); @@ -5915,6 +5918,7 @@ static void check_new_map(struct ceph_mds_client *mdsc, "mds%d reconnect failed: %d\n", i, rc); mutex_lock(&mdsc->mutex); + ceph_put_mds_session(s); } /* @@ -5927,9 +5931,11 @@ 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);