CVE-2024-26781: In the Linux kernel, the following vulnerability has been resolved:  mptcp: fix possible deadlock in subflow diag  Syzbot and Eric reported a lockdep splat in the subflow diag:     WARNING: possible circular locking dependency detected    6.8.0-rc4-syzkaller-00212-g40b9385dd8e6 #0 Not tainted     syz-executor.2/24141 is trying to acquire lock:    ffff888045870130 (k-sk_lock-AF_INET6){+.+.}-{0:0}, at:    tcp_diag_put_ulp net/ipv4/tcp_diag.c:100 [inline]    ffff888045870130 (k-sk_lock-AF_INET6){+.+.}-{0:0}, at:    tcp_diag_get_aux+0x738/0x830 net/ipv4/tcp_diag.c:137     but task is already holding lock:    ffffc9000135e488 (&h->lhash2[i].lock){+.+.}-{2:2}, at: spin_lock    include/linux/spinlock.h:351 [inline]    ffffc9000135e488 (&h->lhash2[i].lock){+.+.}-{2:2}, at:    inet_diag_dump_icsk+0x39f/0x1f80 net/ipv4/inet_diag.c:1038     which lock already depends on the new lock.     the existing dependency chain (in reverse order) is:     -> #1 (&h->lhash2[i].lock){+.+.}-{2:2}:    lock_acquire+0x1e3/0x530 kernel/locking/lockdep.c:5754    __raw_spin_lock include/linux/spinlock_api_smp.h:133 [inline]    _raw_spin_lock+0x2e/0x40 kernel/locking/spinlock.c:154    spin_lock include/linux/spinlock.h:351 [inline]    __inet_hash+0x335/0xbe0 net/ipv4/inet_hashtables.c:743    inet_csk_listen_start+0x23a/0x320 net/ipv4/inet_connection_sock.c:1261    __inet_listen_sk+0x2a2/0x770 net/ipv4/af_inet.c:217    inet_listen+0xa3/0x110 net/ipv4/af_inet.c:239    rds_tcp_listen_init+0x3fd/0x5a0 net/rds/tcp_listen.c:316    rds_tcp_init_net+0x141/0x320 net/rds/tcp.c:577    ops_init+0x352/0x610 net/core/net_namespace.c:136    __register_pernet_operations net/core/net_namespace.c:1214 [inline]    register_pernet_operations+0x2cb/0x660 net/core/net_namespace.c:1283    register_pernet_device+0x33/0x80 net/core/net_namespace.c:1370    rds_tcp_init+0x62/0xd0 net/rds/tcp.c:735    do_one_initcall+0x238/0x830 init/main.c:1236    do_initcall_level+0x157/0x210 init/main.c:1298    do_initcalls+0x3f/0x80 init/main.c:1314    kernel_init_freeable+0x42f/0x5d0 init/main.c:1551    kernel_init+0x1d/0x2a0 init/main.c:1441    ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147    ret_from_fork_asm+0x1b/0x30 arch/x86/entry/entry_64.S:242     -> #0 (k-sk_lock-AF_INET6){+.+.}-{0:0}:    check_prev_add kernel/locking/lockdep.c:3134 [inline]    check_prevs_add kernel/locking/lockdep.c:3253 [inline]    validate_chain+0x18ca/0x58e0 kernel/locking/lockdep.c:3869    __lock_acquire+0x1345/0x1fd0 kernel/locking/lockdep.c:5137    lock_acquire+0x1e3/0x530 kernel/locking/lockdep.c:5754    lock_sock_fast include/net/sock.h:1723 [inline]    subflow_get_info+0x166/0xd20 net/mptcp/diag.c:28    tcp_diag_put_ulp net/ipv4/tcp_diag.c:100 [inline]    tcp_diag_get_aux+0x738/0x830 net/ipv4/tcp_diag.c:137    inet_sk_diag_fill+0x10ed/0x1e00 net/ipv4/inet_diag.c:345    inet_diag_dump_icsk+0x55b/0x1f80 net/ipv4/inet_diag.c:1061    __inet_diag_dump+0x211/0x3a0 net/ipv4/inet_diag.c:1263    inet_diag_dump_compat+0x1c1/0x2d0 net/ipv4/inet_diag.c:1371    netlink_dump+0x59b/0xc80 net/netlink/af_netlink.c:2264    __netlink_dump_start+0x5df/0x790 net/netlink/af_netlink.c:2370    netlink_dump_start include/linux/netlink.h:338 [inline]    inet_diag_rcv_msg_compat+0x209/0x4c0 net/ipv4/inet_diag.c:1405    sock_diag_rcv_msg+0xe7/0x410    netlink_rcv_skb+0x1e3/0x430 net/netlink/af_netlink.c:2543    sock_diag_rcv+0x2a/0x40 net/core/sock_diag.c:280    netlink_unicast_kernel net/netlink/af_netlink.c:1341 [inline]    netlink_unicast+0x7ea/0x980 net/netlink/af_netlink.c:1367    netlink_sendmsg+0xa3b/0xd70 net/netlink/af_netlink.c:1908    sock_sendmsg_nosec net/socket.c:730 [inline]    __sock_sendmsg+0x221/0x270 net/socket.c:745    ____sys_sendmsg+0x525/0x7d0 net/socket.c:2584    ___sys_sendmsg net/socket.c:2638 [inline]    __sys_sendmsg+0x2b0/0x3a0 net/socket.c:2667    do_syscall_64+0xf9/0x240    entry_SYSCALL_64_after_hwframe+0x6f/0x77  As noted by Eric we can break the lock dependency chain avoid dumping  ---truncated---