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[209.147.138.4]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-33ba4e4fb3esm30593846eec.7.2026.09.14.22.19.26 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 14 Sep 2026 22:19:26 -0700 (PDT) From: Xiang Mei To: idryomov@gmail.com, amarkuze@redhat.com, slava@dubeyko.com Cc: ceph-devel@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, co+f8e3e01d8dda8689@bugs.sh, Xiang Mei Subject: [PATCH] ceph: reject mdsmaps that claim more than CEPH_MAX_MDS ranks Date: Mon, 14 Sep 2026 22:19:24 -0700 Message-ID: <20260915051924.737109-1-xmei5@asu.edu> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" check_new_map() sizes its export-target bitmap from CEPH_MAX_MDS but walks it with newmap->possible_max_rank, which comes straight off the wire: ceph_mdsmap_decode() sets it to max(m_num_active_mds, m_max_mds), then overwrites it with the size of the "in" set. Neither is bounded by CEPH_MAX_MDS, only by m_info allocating, so a monitor announcing more ranks than the bitmap holds makes test_bit() read past the end of targets[]. The clear_bit() loop above indexes the same bitmap, though it is additionally bounded by mdsc->max_sessions. The map arrives on the monitor connection, which is unauthenticated in legacy msgr mode. CEPH_MAX_MDS is a protocol constant from src/mds/mdstypes.h, and the reserved inode ranges in super.h are laid out one rank apart over that span, so a map claiming more ranks is corrupt. Reject it where the rank space is established rather than letting the count reach check_new_map(). BUG: KASAN: stack-out-of-bounds in check_new_map (fs/ceph/mds_client.c:59= 68) Read of size 8 at addr ffffc90000ac7798 by task kworker/1:2/127 Workqueue: ceph-msgr ceph_con_workfn Call Trace: dump_stack_lvl (lib/dump_stack.c:94 lib/dump_stack.c:120) print_report (mm/kasan/report.c:378 mm/kasan/report.c:482) kasan_report (mm/kasan/report.c:595) kasan_check_range (mm/kasan/generic.c:186 mm/kasan/generic.c:200) check_new_map (fs/ceph/mds_client.c:5968) ceph_mdsc_handle_mdsmap (fs/ceph/mds_client.c:7060) extra_mon_dispatch (fs/ceph/super.c:802) mon_dispatch (net/ceph/mon_client.c:1483) ceph_con_process_message (net/ceph/messenger.c:1424) ceph_con_v1_try_read (net/ceph/messenger_v1.c:1430) ceph_con_workfn (net/ceph/messenger.c:1576) process_one_work (kernel/workqueue.c:3396) worker_thread (kernel/workqueue.c:3479 kernel/workqueue.c:3560) kthread (kernel/kthread.c:436) ret_from_fork (arch/x86/kernel/process.c:158) ret_from_fork_asm (arch/x86/entry/entry_64.S:245) The buggy address belongs to stack of task kworker/1:2/127 and is located at offset 288 in frame: check_new_map (fs/ceph/mds_client.c:5846) This frame has 1 object: [32, 288) 'targets' Cc: stable@vger.kernel.org Fixes: d517b3983dd3 ("ceph: reconnect to the export targets on new mdsmaps") Reported-by: Assisted-by: LLM Signed-off-by: Xiang Mei --- fs/ceph/mdsmap.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/fs/ceph/mdsmap.c b/fs/ceph/mdsmap.c index 53079ef34c3a..5e3b8c3ca502 100644 --- a/fs/ceph/mdsmap.c +++ b/fs/ceph/mdsmap.c @@ -170,6 +170,10 @@ struct ceph_mdsmap *ceph_mdsmap_decode(struct ceph_mds= _client *mdsc, void **p, * and the mds rank >=3D m_num_active_mds. */ m->possible_max_rank =3D max(m->m_num_active_mds, m->m_max_mds); + if (m->possible_max_rank > CEPH_MAX_MDS) { + err =3D -EIO; + goto corrupt; + } =20 m->m_info =3D kzalloc_objs(*m->m_info, m->possible_max_rank, GFP_NOFS); if (!m->m_info) @@ -316,6 +320,10 @@ struct ceph_mdsmap *ceph_mdsmap_decode(struct ceph_mds= _client *mdsc, void **p, { int num_laggy =3D 0; ceph_decode_32_safe(p, end, n, bad_ext); + if (n > CEPH_MAX_MDS) { + err =3D -EIO; + goto corrupt; + } ceph_decode_need(p, end, sizeof(u32) * n, bad_ext); =20 for (i =3D 0; i < n; i++) { --=20 2.43.0