======================================================
WARNING: possible circular locking dependency detected
5.11.0-syzkaller #0 Not tainted
------------------------------------------------------
syz-executor905/8822 is trying to acquire lock:
ffffffff8d678fe8 (rtnl_mutex){+.+.}-{3:3}, at: ipv6_sock_mc_close+0xd7/0x110 net/ipv6/mcast.c:323

but task is already holding lock:
ffff888024390120 (sk_lock-AF_INET6){+.+.}-{0:0}, at: lock_sock include/net/sock.h:1600 [inline]
ffff888024390120 (sk_lock-AF_INET6){+.+.}-{0:0}, at: mptcp6_release+0x57/0x130 net/mptcp/protocol.c:3507

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #1 (sk_lock-AF_INET6){+.+.}-{0:0}:
       lock_sock_nested+0xca/0x120 net/core/sock.c:3071
       lock_sock include/net/sock.h:1600 [inline]
       gtp_encap_enable_socket+0x277/0x4a0 drivers/net/gtp.c:824
       gtp_encap_enable drivers/net/gtp.c:855 [inline]
       gtp_newlink+0x2b3/0xc60 drivers/net/gtp.c:683
       __rtnl_newlink+0x1059/0x1710 net/core/rtnetlink.c:3443
       rtnl_newlink+0x64/0xa0 net/core/rtnetlink.c:3491
       rtnetlink_rcv_msg+0x44e/0xad0 net/core/rtnetlink.c:5553
       netlink_rcv_skb+0x153/0x420 net/netlink/af_netlink.c:2502
       netlink_unicast_kernel net/netlink/af_netlink.c:1312 [inline]
       netlink_unicast+0x533/0x7d0 net/netlink/af_netlink.c:1338
       netlink_sendmsg+0x856/0xd90 net/netlink/af_netlink.c:1927
       sock_sendmsg_nosec net/socket.c:654 [inline]
       sock_sendmsg+0xcf/0x120 net/socket.c:674
       ____sys_sendmsg+0x6e8/0x810 net/socket.c:2350
       ___sys_sendmsg+0xf3/0x170 net/socket.c:2404
       __sys_sendmsg+0xe5/0x1b0 net/socket.c:2437
       do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
       entry_SYSCALL_64_after_hwframe+0x44/0xae

-> #0 (rtnl_mutex){+.+.}-{3:3}:
       check_prev_add kernel/locking/lockdep.c:2936 [inline]
       check_prevs_add kernel/locking/lockdep.c:3059 [inline]
       validate_chain kernel/locking/lockdep.c:3674 [inline]
       __lock_acquire+0x2b14/0x54c0 kernel/locking/lockdep.c:4900
       lock_acquire kernel/locking/lockdep.c:5510 [inline]
       lock_acquire+0x1ab/0x730 kernel/locking/lockdep.c:5475
       __mutex_lock_common kernel/locking/mutex.c:946 [inline]
       __mutex_lock+0x139/0x1120 kernel/locking/mutex.c:1093
       ipv6_sock_mc_close+0xd7/0x110 net/ipv6/mcast.c:323
       mptcp6_release+0xb9/0x130 net/mptcp/protocol.c:3515
       __sock_release+0xcd/0x280 net/socket.c:599
       sock_close+0x18/0x20 net/socket.c:1258
       __fput+0x288/0x920 fs/file_table.c:280
       task_work_run+0xdd/0x1a0 kernel/task_work.c:140
       tracehook_notify_resume include/linux/tracehook.h:189 [inline]
       exit_to_user_mode_loop kernel/entry/common.c:174 [inline]
       exit_to_user_mode_prepare+0x249/0x250 kernel/entry/common.c:208
       __syscall_exit_to_user_mode_work kernel/entry/common.c:290 [inline]
       syscall_exit_to_user_mode+0x19/0x50 kernel/entry/common.c:301
       entry_SYSCALL_64_after_hwframe+0x44/0xae

other info that might help us debug this:

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(sk_lock-AF_INET6);
                               lock(rtnl_mutex);
                               lock(sk_lock-AF_INET6);
  lock(rtnl_mutex);

 *** DEADLOCK ***

2 locks held by syz-executor905/8822:
 #0: ffff888033080750 (&sb->s_type->i_mutex_key#13){+.+.}-{3:3}, at: inode_lock include/linux/fs.h:775 [inline]
 #0: ffff888033080750 (&sb->s_type->i_mutex_key#13){+.+.}-{3:3}, at: __sock_release+0x86/0x280 net/socket.c:598
 #1: ffff888024390120 (sk_lock-AF_INET6){+.+.}-{0:0}, at: lock_sock include/net/sock.h:1600 [inline]
 #1: ffff888024390120 (sk_lock-AF_INET6){+.+.}-{0:0}, at: mptcp6_release+0x57/0x130 net/mptcp/protocol.c:3507

stack backtrace:
CPU: 1 PID: 8822 Comm: syz-executor905 Not tainted 5.11.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:79 [inline]
 dump_stack+0xfa/0x151 lib/dump_stack.c:120
 check_noncircular+0x25f/0x2e0 kernel/locking/lockdep.c:2127
 check_prev_add kernel/locking/lockdep.c:2936 [inline]
 check_prevs_add kernel/locking/lockdep.c:3059 [inline]
 validate_chain kernel/locking/lockdep.c:3674 [inline]
 __lock_acquire+0x2b14/0x54c0 kernel/locking/lockdep.c:4900
 lock_acquire kernel/locking/lockdep.c:5510 [inline]
 lock_acquire+0x1ab/0x730 kernel/locking/lockdep.c:5475
 __mutex_lock_common kernel/locking/mutex.c:946 [inline]
 __mutex_lock+0x139/0x1120 kernel/locking/mutex.c:1093
 ipv6_sock_mc_close+0xd7/0x110 net/ipv6/mcast.c:323
 mptcp6_release+0xb9/0x130 net/mptcp/protocol.c:3515
 __sock_release+0xcd/0x280 net/socket.c:599
 sock_close+0x18/0x20 net/socket.c:1258
 __fput+0x288/0x920 fs/file_table.c:280
 task_work_run+0xdd/0x1a0 kernel/task_work.c:140
 tracehook_notify_resume include/linux/tracehook.h:189 [inline]
 exit_to_user_mode_loop kernel/entry/common.c:174 [inline]
 exit_to_user_mode_prepare+0x249/0x250 kernel/entry/common.c:208
 __syscall_exit_to_user_mode_work kernel/entry/common.c:290 [inline]
 syscall_exit_to_user_mode+0x19/0x50 kernel/entry/common.c:301
 entry_SYSCALL_64_after_hwframe+0x44/0xae
RIP: 0033:0x405b73
Code: c7 c2 c0 ff ff ff f7 d8 64 89 02 48 c7 c0 ff ff ff ff eb b7 0f 1f 00 64 8b 04 25 18 00 00 00 85 c0 75 14 b8 03 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 45 c3 0f 1f 40 00 48 83 ec 18 89 7c 24 0c e8
RSP: 002b:00007ffdbac4d208 EFLAGS: 00000246 ORIG_RAX: 0000000000000003
RAX: 0000000000000000 RBX: 0000000000000006 RCX: 0000000000405b73
RDX: 000000000000002a RSI: 0000000000000029 RDI: 0000000000000005
RBP: 0000000000000000 R08: 0000000000000088 R09: 0000000000f0b5ff
R10: 00000000200001c0 R11: 0000000000000246 R12: 0000000000010bda
R13: 00007ffdbac4d230 R14: 00007ffdbac4d220 R15: 00007ffdbac4d214