From: Aleksandr Nogikh When parsing the Ceph messenger v2 protocol banner, the `payload_len` field is decoded from the banner prefix. If a client sends a banner with a `payload_len` of 0, the kernel sets up a 0-length socket read. This violates an invariant in the state machine, triggering a warning in `populate_in_iter()`: ------------[ cut here ]------------ !iov_iter_count(&con->v2.in_iter) WARNING: net/ceph/messenger_v2.c:3129 at populate_in_iter net/ceph/messenger_v2.c:3129 [inline], CPU#1: kworker/1:3/5070 WARNING: net/ceph/messenger_v2.c:3129 at ceph_con_v2_try_read+0x6634/0x6810 net/ceph/messenger_v2.c:3159, CPU#1: kworker/1:3/5070 ... Call Trace: ceph_con_workfn+0x1f5/0x14a0 net/ceph/messenger.c:1575 process_one_work kernel/workqueue.c:3322 [inline] process_scheduled_works+0xa8e/0x14e0 kernel/workqueue.c:3405 worker_thread+0xa47/0xfb0 kernel/workqueue.c:3486 kthread+0x388/0x470 kernel/kthread.c:436 ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 According to the msgr2 protocol specification, the banner payload is expected to contain at least two 64-bit integers (`server_feat` and `server_req_feat`). Therefore, `payload_len` must be at least 16 bytes. Fix this by adding a check in `process_banner_prefix()` to reject a `payload_len` smaller than 16 bytes. This prevents the 0-length read and correctly aborts the connection with a protocol error. Fixes: cd1a677cad99 ("libceph, ceph: implement msgr2.1 protocol (crc and secure modes)") Assisted-by: Gemini:gemini-3.5-flash Gemini:gemini-3.1-pro-preview syzbot Reported-by: syzbot+87c7c2d63c44e41c77a3@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=87c7c2d63c44e41c77a3 Link: https://syzkaller.appspot.com/ai_job?id=c8ca3d63-717a-4933-89ec-f3d761b8690d Signed-off-by: Aleksandr Nogikh --- diff --git a/net/ceph/messenger_v2.c b/net/ceph/messenger_v2.c index 05f6eea29..b323b61e7 100644 --- a/net/ceph/messenger_v2.c +++ b/net/ceph/messenger_v2.c @@ -2142,6 +2142,11 @@ static int process_banner_prefix(struct ceph_connection *con) payload_len = ceph_decode_16(&p); dout("%s con %p payload_len %d\n", __func__, con, payload_len); + if (payload_len < sizeof(u64) + sizeof(u64)) { + con->error_msg = "protocol error, bad banner payload len"; + return -EINVAL; + } + return prepare_read_banner_payload(con, payload_len); } base-commit: f5098b6bae761e346ebcd9da7f95622c04733cff -- See https://goo.gle/syzbot-ai-patches for information about AI-generated patches. You can comment on the patch as usual, syzbot will try to address the comments and send a new version of the patch if necessary. syzbot engineers can be reached at syzkaller@googlegroups.com.