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[2003:dc:6f04:b700:230:64ff:fe74:809]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-c260d6e1c93sm122438866b.63.2026.09.04.08.03.10 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 04 Sep 2026 08:03:11 -0700 (PDT) From: Max Kellermann To: idryomov@gmail.com, amarkuze@redhat.com, xiubo.li@clyso.com, ceph-devel@vger.kernel.org, linux-kernel@vger.kernel.org Cc: Max Kellermann , stable@vger.kernel.org Subject: [PATCH v4 2/3] ceph: stop checking a stale MDS map after dropping mutex Date: Fri, 4 Sep 2026 17:03:03 +0200 Message-ID: <20260904150304.49104-3-max.kellermann@ionos.com> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260904150304.49104-1-max.kellermann@ionos.com> References: <20260904150304.49104-1-max.kellermann@ionos.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit check_new_map() drops `mdsc->mutex` in several slow paths. Another map handler can install a newer map and destroy the map being checked before the original invocation re-locks the mutex. Continuing to dereference newmap after that results in a use-after-free. Use the `mdsmap->m_epoch` field to identify stale maps. Fixes: 2f2dc053404f ("ceph: MDS client") Cc: stable@vger.kernel.org Signed-off-by: Max Kellermann --- fs/ceph/mds_client.c | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+) diff --git a/fs/ceph/mds_client.c b/fs/ceph/mds_client.c index d36a114747ae..86d592f06196 100644 --- a/fs/ceph/mds_client.c +++ b/fs/ceph/mds_client.c @@ -5844,6 +5844,7 @@ static void check_new_map(struct ceph_mds_client *mdsc, struct ceph_mdsmap *newmap, struct ceph_mdsmap *oldmap) { + u32 map_epoch = newmap->m_epoch; int i, j, err; int oldstate, newstate; struct ceph_mds_session *s; @@ -5887,6 +5888,8 @@ static void check_new_map(struct ceph_mds_client *mdsc, ceph_put_mds_session(s); mutex_lock(&mdsc->mutex); + if (mdsc->mdsmap->m_epoch != map_epoch) + return; kick_requests(mdsc, i); continue; } @@ -5898,6 +5901,11 @@ static void check_new_map(struct ceph_mds_client *mdsc, mutex_unlock(&mdsc->mutex); mutex_lock(&s->s_mutex); mutex_lock(&mdsc->mutex); + if (mdsc->mdsmap->m_epoch != map_epoch) { + mutex_unlock(&s->s_mutex); + ceph_put_mds_session(s); + return; + } ceph_con_close(&s->s_con); mutex_unlock(&s->s_mutex); s->s_state = CEPH_MDS_SESSION_RESTARTING; @@ -5921,6 +5929,10 @@ static void check_new_map(struct ceph_mds_client *mdsc, "mds%d reconnect failed: %d\n", i, rc); mutex_lock(&mdsc->mutex); + if (mdsc->mdsmap->m_epoch != map_epoch) { + ceph_put_mds_session(s); + return; + } } /* @@ -5936,6 +5948,11 @@ static void check_new_map(struct ceph_mds_client *mdsc, mutex_unlock(&mdsc->mutex); mutex_lock(&s->s_mutex); mutex_lock(&mdsc->mutex); + if (mdsc->mdsmap->m_epoch != map_epoch) { + mutex_unlock(&s->s_mutex); + ceph_put_mds_session(s); + return; + } ceph_kick_flushing_caps(mdsc, s); mutex_unlock(&s->s_mutex); wake_up_session_caps(s, RECONNECT); @@ -5991,6 +6008,8 @@ static void check_new_map(struct ceph_mds_client *mdsc, i, err); ceph_put_mds_session(s); mutex_lock(&mdsc->mutex); + if (mdsc->mdsmap->m_epoch != map_epoch) + return; } for (i = 0; i < newmap->possible_max_rank && i < mdsc->max_sessions; i++) { -- 2.47.3