From 7286b2ffe04d4b39b4e9884f714792589d94f316 Mon Sep 17 00:00:00 2001 From: Xiang Mei Date: Mon, 14 Sep 2026 19:17:10 -0700 Subject: [PATCH] ceph: require the dentry lease record to cover struct ceph_mds_reply_lease parse_reply_info_lease() reads a 32-bit struct_len off the wire and only checks that many bytes are present, without requiring struct_len to cover sizeof(struct ceph_mds_reply_lease) (10 bytes). A malicious MDS can declare a shorter record and still get the pointer published: the following *p += sizeof(**lease) overshoot is undone by *p = lend, so nothing downstream rejects the reply. ceph_fill_trace() -> update_dentry_lease() then reads 10 bytes through that pointer on any lookup on a mounted CephFS, running past the end of the message front. Require the record to cover the structure, matching the sibling parse_reply_info_dir(). A conforming MDS always encodes the full 10 bytes. BUG: KASAN: slab-out-of-bounds in __update_dentry_lease.constprop.0 (fs/ceph/inode.c:1459) Read of size 4 at addr ffff888026c63d65 by task kworker/0:3/2366 Workqueue: ceph-msgr ceph_con_workfn Call Trace: __update_dentry_lease.constprop.0 (fs/ceph/inode.c:1459) ceph_fill_trace (fs/ceph/inode.c:1474 fs/ceph/inode.c:1823) mds_dispatch (fs/ceph/mds_client.c:4229 fs/ceph/mds_client.c:7225) 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 is located 357 bytes inside of allocated 360-byte region [ffff888026c63c00, ffff888026c63d68) Cc: stable@vger.kernel.org Fixes: 4ac4c23eaa38 ("ceph: decode alternate_name in lease info") Reported-by: co+f92fbe44e3c6df69@bugs.sh Assisted-by: LLM Signed-off-by: Xiang Mei Reviewed-by: Alex Markuze Signed-off-by: Ilya Dryomov --- fs/ceph/mds_client.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/fs/ceph/mds_client.c b/fs/ceph/mds_client.c index a3756293ed71..98c8736cced2 100644 --- a/fs/ceph/mds_client.c +++ b/fs/ceph/mds_client.c @@ -403,6 +403,8 @@ static int parse_reply_info_lease(void **p, void *end, lend = *p + struct_len; ceph_decode_need(p, end, struct_len, bad); + if (struct_len < sizeof(**lease)) + goto bad; *lease = *p; *p += sizeof(**lease);