syzbot

======================================================
WARNING: possible circular locking dependency detected
6.8.0-rc1-syzkaller-00356-g8a696a29c690 #0 Not tainted
------------------------------------------------------
syz-executor.1/2542 is trying to acquire lock:
ffff88808b5df9e8 (rlock-AF_UNIX){+.+.}-{2:2}, at: skb_queue_tail+0x36/0x120 net/core/skbuff.c:3863

but task is already holding lock:
ffff88808b5dfe70 (&u->lock/1){+.+.}-{2:2}, at: unix_dgram_sendmsg+0xfc7/0x2200 net/unix/af_unix.c:2089

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #1 (&u->lock/1){+.+.}-{2:2}:
       lock_acquire+0x1e3/0x530 kernel/locking/lockdep.c:5754
       _raw_spin_lock_nested+0x31/0x40 kernel/locking/spinlock.c:378
       sk_diag_dump_icons net/unix/diag.c:87 [inline]
       sk_diag_fill+0x6ea/0xfe0 net/unix/diag.c:157
       sk_diag_dump net/unix/diag.c:196 [inline]
       unix_diag_dump+0x3e9/0x630 net/unix/diag.c:220
       netlink_dump+0x5c1/0xcd0 net/netlink/af_netlink.c:2264
       __netlink_dump_start+0x5d7/0x780 net/netlink/af_netlink.c:2370
       netlink_dump_start include/linux/netlink.h:338 [inline]
       unix_diag_handler_dump+0x1c3/0x8f0 net/unix/diag.c:319
       sock_diag_rcv_msg+0xe3/0x400
       netlink_rcv_skb+0x1df/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+0x7e6/0x980 net/netlink/af_netlink.c:1367
       netlink_sendmsg+0xa37/0xd70 net/netlink/af_netlink.c:1908
       sock_sendmsg_nosec net/socket.c:730 [inline]
       __sock_sendmsg net/socket.c:745 [inline]
       sock_write_iter+0x39a/0x520 net/socket.c:1160
       call_write_iter include/linux/fs.h:2085 [inline]
       new_sync_write fs/read_write.c:497 [inline]
       vfs_write+0xa74/0xca0 fs/read_write.c:590
       ksys_write+0x1a0/0x2c0 fs/read_write.c:643
       do_syscall_x64 arch/x86/entry/common.c:52 [inline]
       do_syscall_64+0xf5/0x230 arch/x86/entry/common.c:83
       entry_SYSCALL_64_after_hwframe+0x63/0x6b

-> #0 (rlock-AF_UNIX){+.+.}-{2:2}:
       check_prev_add kernel/locking/lockdep.c:3134 [inline]
       check_prevs_add kernel/locking/lockdep.c:3253 [inline]
       validate_chain+0x1909/0x5ab0 kernel/locking/lockdep.c:3869
       __lock_acquire+0x1345/0x1fd0 kernel/locking/lockdep.c:5137
       lock_acquire+0x1e3/0x530 kernel/locking/lockdep.c:5754
       __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
       _raw_spin_lock_irqsave+0xd5/0x120 kernel/locking/spinlock.c:162
       skb_queue_tail+0x36/0x120 net/core/skbuff.c:3863
       unix_dgram_sendmsg+0x15d9/0x2200 net/unix/af_unix.c:2112
       sock_sendmsg_nosec net/socket.c:730 [inline]
       __sock_sendmsg net/socket.c:745 [inline]
       ____sys_sendmsg+0x592/0x890 net/socket.c:2584
       ___sys_sendmsg net/socket.c:2638 [inline]
       __sys_sendmmsg+0x3b2/0x730 net/socket.c:2724
       __do_sys_sendmmsg net/socket.c:2753 [inline]
       __se_sys_sendmmsg net/socket.c:2750 [inline]
       __x64_sys_sendmmsg+0xa0/0xb0 net/socket.c:2750
       do_syscall_x64 arch/x86/entry/common.c:52 [inline]
       do_syscall_64+0xf5/0x230 arch/x86/entry/common.c:83
       entry_SYSCALL_64_after_hwframe+0x63/0x6b

other info that might help us debug this:

 Possible unsafe locking scenario:

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

 *** DEADLOCK ***

1 lock held by syz-executor.1/2542:
 #0: ffff88808b5dfe70 (&u->lock/1){+.+.}-{2:2}, at: unix_dgram_sendmsg+0xfc7/0x2200 net/unix/af_unix.c:2089

stack backtrace:
CPU: 1 PID: 2542 Comm: syz-executor.1 Not tainted 6.8.0-rc1-syzkaller-00356-g8a696a29c690 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/17/2023
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0x1e7/0x2d0 lib/dump_stack.c:106
 check_noncircular+0x366/0x490 kernel/locking/lockdep.c:2187
 check_prev_add kernel/locking/lockdep.c:3134 [inline]
 check_prevs_add kernel/locking/lockdep.c:3253 [inline]
 validate_chain+0x1909/0x5ab0 kernel/locking/lockdep.c:3869
 __lock_acquire+0x1345/0x1fd0 kernel/locking/lockdep.c:5137
 lock_acquire+0x1e3/0x530 kernel/locking/lockdep.c:5754
 __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
 _raw_spin_lock_irqsave+0xd5/0x120 kernel/locking/spinlock.c:162
 skb_queue_tail+0x36/0x120 net/core/skbuff.c:3863
 unix_dgram_sendmsg+0x15d9/0x2200 net/unix/af_unix.c:2112
 sock_sendmsg_nosec net/socket.c:730 [inline]
 __sock_sendmsg net/socket.c:745 [inline]
 ____sys_sendmsg+0x592/0x890 net/socket.c:2584
 ___sys_sendmsg net/socket.c:2638 [inline]
 __sys_sendmmsg+0x3b2/0x730 net/socket.c:2724
 __do_sys_sendmmsg net/socket.c:2753 [inline]
 __se_sys_sendmmsg net/socket.c:2750 [inline]
 __x64_sys_sendmmsg+0xa0/0xb0 net/socket.c:2750
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xf5/0x230 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x63/0x6b
RIP: 0033:0x7f26d887cda9
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 e1 20 00 00 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 73 01 c3 48 c7 c1 b0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f26d95a60c8 EFLAGS: 00000246 ORIG_RAX: 0000000000000133
RAX: ffffffffffffffda RBX: 00007f26d89abf80 RCX: 00007f26d887cda9
RDX: 000000000000003e RSI: 00000000200bd000 RDI: 0000000000000004
RBP: 00007f26d88c947a R08: 0000000000000000 R09: 0000000000000000
R10: 00000000000008c0 R11: 0000000000000246 R12: 0000000000000000
R13: 000000000000000b R14: 00007f26d89abf80 R15: 00007ffcfe081a68
 </TASK>