syzbot

======================================================
WARNING: possible circular locking dependency detected
5.0.0+ #15 Not tainted
------------------------------------------------------
syz-executor.2/844 is trying to acquire lock:
00000000520483ab (rlock-AF_UNIX){+.+.}, at: skb_queue_tail+0x26/0x150 net/core/skbuff.c:2972

but task is already holding lock:
00000000de9aec21 (&(&u->lock)->rlock/1){+.+.}, at: unix_state_double_lock net/unix/af_unix.c:1087 [inline]
00000000de9aec21 (&(&u->lock)->rlock/1){+.+.}, at: unix_state_double_lock+0x80/0xb0 net/unix/af_unix.c:1079

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #1 (&(&u->lock)->rlock/1){+.+.}:
       lock_acquire+0x16f/0x3f0 kernel/locking/lockdep.c:4202
       _raw_spin_lock_nested+0x35/0x50 kernel/locking/spinlock.c:354
       sk_diag_dump_icons net/unix/diag.c:83 [inline]
       sk_diag_fill.isra.0+0x9c0/0xf30 net/unix/diag.c:145
       sk_diag_dump net/unix/diag.c:179 [inline]
       unix_diag_dump+0x35c/0x550 net/unix/diag.c:207
       netlink_dump+0x55d/0xfb0 net/netlink/af_netlink.c:2252
       __netlink_dump_start+0x5b4/0x7e0 net/netlink/af_netlink.c:2360
       netlink_dump_start include/linux/netlink.h:226 [inline]
       unix_diag_handler_dump+0x390/0x740 net/unix/diag.c:308
       __sock_diag_cmd net/core/sock_diag.c:232 [inline]
       sock_diag_rcv_msg+0x322/0x410 net/core/sock_diag.c:263
       netlink_rcv_skb+0x17a/0x460 net/netlink/af_netlink.c:2485
       sock_diag_rcv+0x2b/0x40 net/core/sock_diag.c:274
       netlink_unicast_kernel net/netlink/af_netlink.c:1310 [inline]
       netlink_unicast+0x536/0x720 net/netlink/af_netlink.c:1336
       netlink_sendmsg+0x8ae/0xd70 net/netlink/af_netlink.c:1925
       sock_sendmsg_nosec net/socket.c:622 [inline]
       sock_sendmsg+0xdd/0x130 net/socket.c:632
       sock_write_iter+0x27c/0x3e0 net/socket.c:923
       call_write_iter include/linux/fs.h:1860 [inline]
       do_iter_readv_writev+0x5e1/0x8e0 fs/read_write.c:680
       do_iter_write fs/read_write.c:956 [inline]
       do_iter_write+0x184/0x610 fs/read_write.c:937
       vfs_writev+0x1b3/0x2f0 fs/read_write.c:1001
       do_writev+0xf6/0x290 fs/read_write.c:1036
       __do_sys_writev fs/read_write.c:1109 [inline]
       __se_sys_writev fs/read_write.c:1106 [inline]
       __x64_sys_writev+0x75/0xb0 fs/read_write.c:1106
       do_syscall_64+0x103/0x610 arch/x86/entry/common.c:290
       entry_SYSCALL_64_after_hwframe+0x49/0xbe

-> #0 (rlock-AF_UNIX){+.+.}:
       check_prevs_add kernel/locking/lockdep.c:2324 [inline]
       validate_chain kernel/locking/lockdep.c:2705 [inline]
       __lock_acquire+0x239c/0x3fb0 kernel/locking/lockdep.c:3692
       lock_acquire+0x16f/0x3f0 kernel/locking/lockdep.c:4202
       __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
       _raw_spin_lock_irqsave+0x95/0xcd kernel/locking/spinlock.c:152
       skb_queue_tail+0x26/0x150 net/core/skbuff.c:2972
       unix_dgram_sendmsg+0xc31/0x11e0 net/unix/af_unix.c:1755
       sock_sendmsg_nosec net/socket.c:622 [inline]
       sock_sendmsg+0xdd/0x130 net/socket.c:632
       ___sys_sendmsg+0x3e2/0x930 net/socket.c:2137
       __sys_sendmmsg+0x1bf/0x4d0 net/socket.c:2232
       __do_sys_sendmmsg net/socket.c:2261 [inline]
       __se_sys_sendmmsg net/socket.c:2258 [inline]
       __x64_sys_sendmmsg+0x9d/0x100 net/socket.c:2258
       do_syscall_64+0x103/0x610 arch/x86/entry/common.c:290
       entry_SYSCALL_64_after_hwframe+0x49/0xbe

other info that might help us debug this:

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&(&u->lock)->rlock/1);
                               lock(rlock-AF_UNIX);
                               lock(&(&u->lock)->rlock/1);
  lock(rlock-AF_UNIX);

 *** DEADLOCK ***

1 lock held by syz-executor.2/844:
 #0: 00000000de9aec21 (&(&u->lock)->rlock/1){+.+.}, at: unix_state_double_lock net/unix/af_unix.c:1087 [inline]
 #0: 00000000de9aec21 (&(&u->lock)->rlock/1){+.+.}, at: unix_state_double_lock+0x80/0xb0 net/unix/af_unix.c:1079

stack backtrace:
CPU: 0 PID: 844 Comm: syz-executor.2 Not tainted 5.0.0+ #15
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x172/0x1f0 lib/dump_stack.c:113
 print_circular_bug.isra.0.cold+0x1cc/0x28f kernel/locking/lockdep.c:1562
 check_prev_add.constprop.0+0xf11/0x23c0 kernel/locking/lockdep.c:2211
 check_prevs_add kernel/locking/lockdep.c:2324 [inline]
 validate_chain kernel/locking/lockdep.c:2705 [inline]
 __lock_acquire+0x239c/0x3fb0 kernel/locking/lockdep.c:3692
 lock_acquire+0x16f/0x3f0 kernel/locking/lockdep.c:4202
 __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
 _raw_spin_lock_irqsave+0x95/0xcd kernel/locking/spinlock.c:152
 skb_queue_tail+0x26/0x150 net/core/skbuff.c:2972
 unix_dgram_sendmsg+0xc31/0x11e0 net/unix/af_unix.c:1755
 sock_sendmsg_nosec net/socket.c:622 [inline]
 sock_sendmsg+0xdd/0x130 net/socket.c:632
 ___sys_sendmsg+0x3e2/0x930 net/socket.c:2137
 __sys_sendmmsg+0x1bf/0x4d0 net/socket.c:2232
 __do_sys_sendmmsg net/socket.c:2261 [inline]
 __se_sys_sendmmsg net/socket.c:2258 [inline]
 __x64_sys_sendmmsg+0x9d/0x100 net/socket.c:2258
 do_syscall_64+0x103/0x610 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x457f29
Code: ad b8 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 0f 83 7b b8 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f670cf55c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000133
RAX: ffffffffffffffda RBX: 0000000000000004 RCX: 0000000000457f29
RDX: 0000000000000080 RSI: 00000000200bd000 RDI: 0000000000000004
RBP: 000000000073bf00 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f670cf566d4
R13: 00000000004c4f12 R14: 00000000004d8c70 R15: 00000000ffffffff