Subject: possible deadlock in skb_queue_tail

From: syzbot <[email-masked]>
Date: Mon, 02 Apr 2018 02:20:01 -0700

Hello,

syzbot hit the following crash on net-next commit
06b19fe9a6df7aaa423cd8404ebe5ac9ec4b2960 (Sun Apr 1 03:37:33 2018 +0000)
Merge branch 'chelsio-inline-tls'
syzbot dashboard link:  
https://syzkaller.appspot.com/bug?extid=6b495100f17ca8554ab9

Unfortunately, I don't have any reproducer for this crash yet.
Raw console output:  
https://syzkaller.appspot.com/x/log.txt?id=6218830443446272
Kernel config:  
https://syzkaller.appspot.com/x/.config?id=3327544840960562528
compiler: gcc (GCC) 7.1.1 20170620

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: [email-masked]
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details.
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======================================================
WARNING: possible circular locking dependency detected
4.16.0-rc6+ #290 Not tainted
------------------------------------------------------
syz-executor7/20971 is trying to acquire lock:
  (&af_unix_sk_receive_queue_lock_key){+.+.}, at: [<00000000271ef0d8>]  
skb_queue_tail+0x26/0x150 net/core/skbuff.c:2899

but task is already holding lock:
  (&(&u->lock)->rlock/1){+.+.}, at: [<000000004e725e14>]  
unix_state_double_lock+0x7b/0xb0 net/unix/af_unix.c:1088

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #1 (&(&u->lock)->rlock/1){+.+.}:
        _raw_spin_lock_nested+0x28/0x40 kernel/locking/spinlock.c:354
        sk_diag_dump_icons net/unix/diag.c:82 [inline]
        sk_diag_fill.isra.4+0xa52/0xfe0 net/unix/diag.c:144
        sk_diag_dump net/unix/diag.c:178 [inline]
        unix_diag_dump+0x400/0x4f0 net/unix/diag.c:206
        netlink_dump+0x492/0xcf0 net/netlink/af_netlink.c:2221
        __netlink_dump_start+0x4ec/0x710 net/netlink/af_netlink.c:2318
        netlink_dump_start include/linux/netlink.h:214 [inline]
        unix_diag_handler_dump+0x3e7/0x750 net/unix/diag.c:307
        __sock_diag_cmd net/core/sock_diag.c:230 [inline]
        sock_diag_rcv_msg+0x204/0x360 net/core/sock_diag.c:261
        netlink_rcv_skb+0x14b/0x380 net/netlink/af_netlink.c:2443
        sock_diag_rcv+0x2a/0x40 net/core/sock_diag.c:272
        netlink_unicast_kernel net/netlink/af_netlink.c:1307 [inline]
        netlink_unicast+0x4c4/0x6b0 net/netlink/af_netlink.c:1333
        netlink_sendmsg+0xa4a/0xe80 net/netlink/af_netlink.c:1896
        sock_sendmsg_nosec net/socket.c:629 [inline]
        sock_sendmsg+0xca/0x110 net/socket.c:639
        sock_write_iter+0x31a/0x5d0 net/socket.c:908
        call_write_iter include/linux/fs.h:1782 [inline]
        new_sync_write fs/read_write.c:469 [inline]
        __vfs_write+0x684/0x970 fs/read_write.c:482
        vfs_write+0x189/0x510 fs/read_write.c:544
        SYSC_write fs/read_write.c:589 [inline]
        SyS_write+0xef/0x220 fs/read_write.c:581
        do_syscall_64+0x281/0x940 arch/x86/entry/common.c:287
        entry_SYSCALL_64_after_hwframe+0x42/0xb7

-> #0 (&af_unix_sk_receive_queue_lock_key){+.+.}:
        lock_acquire+0x1d5/0x580 kernel/locking/lockdep.c:3920
        __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
        _raw_spin_lock_irqsave+0x96/0xc0 kernel/locking/spinlock.c:152
        skb_queue_tail+0x26/0x150 net/core/skbuff.c:2899
        unix_dgram_sendmsg+0xa30/0x1610 net/unix/af_unix.c:1807
        sock_sendmsg_nosec net/socket.c:629 [inline]
        sock_sendmsg+0xca/0x110 net/socket.c:639
        ___sys_sendmsg+0x320/0x8b0 net/socket.c:2047
        __sys_sendmmsg+0x1ee/0x620 net/socket.c:2137
        SYSC_sendmmsg net/socket.c:2168 [inline]
        SyS_sendmmsg+0x35/0x60 net/socket.c:2163
        do_syscall_64+0x281/0x940 arch/x86/entry/common.c:287
        entry_SYSCALL_64_after_hwframe+0x42/0xb7

other info that might help us debug this:

  Possible unsafe locking scenario:

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

  *** DEADLOCK ***

1 lock held by syz-executor7/20971:
  #0:  (&(&u->lock)->rlock/1){+.+.}, at: [<000000004e725e14>]  
unix_state_double_lock+0x7b/0xb0 net/unix/af_unix.c:1088

stack backtrace:
CPU: 0 PID: 20971 Comm: syz-executor7 Not tainted 4.16.0-rc6+ #290
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
Call Trace:
  __dump_stack lib/dump_stack.c:17 [inline]
  dump_stack+0x194/0x24d lib/dump_stack.c:53
  print_circular_bug.isra.38+0x2cd/0x2dc kernel/locking/lockdep.c:1223
  check_prev_add kernel/locking/lockdep.c:1863 [inline]
  check_prevs_add kernel/locking/lockdep.c:1976 [inline]
  validate_chain kernel/locking/lockdep.c:2417 [inline]
  __lock_acquire+0x30a8/0x3e00 kernel/locking/lockdep.c:3431
  lock_acquire+0x1d5/0x580 kernel/locking/lockdep.c:3920
  __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
  _raw_spin_lock_irqsave+0x96/0xc0 kernel/locking/spinlock.c:152
  skb_queue_tail+0x26/0x150 net/core/skbuff.c:2899
  unix_dgram_sendmsg+0xa30/0x1610 net/unix/af_unix.c:1807
  sock_sendmsg_nosec net/socket.c:629 [inline]
  sock_sendmsg+0xca/0x110 net/socket.c:639
  ___sys_sendmsg+0x320/0x8b0 net/socket.c:2047
  __sys_sendmmsg+0x1ee/0x620 net/socket.c:2137
  SYSC_sendmmsg net/socket.c:2168 [inline]
  SyS_sendmmsg+0x35/0x60 net/socket.c:2163
  do_syscall_64+0x281/0x940 arch/x86/entry/common.c:287
  entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x455269
RSP: 002b:00007f71ffad6c68 EFLAGS: 00000246 ORIG_RAX: 0000000000000133
RAX: ffffffffffffffda RBX: 00007f71ffad76d4 RCX: 0000000000455269
RDX: 04924924924924f4 RSI: 0000000020000200 RDI: 0000000000000016
RBP: 000000000072bf58 R08: 0000000000000000 R09: 0000000000000000
R10: 00000000200000d4 R11: 0000000000000246 R12: 00000000ffffffff
R13: 00000000000004ca R14: 00000000006f9390 R15: 0000000000000001
IPVS: Unknown mcast interface: bcsh0
IPVS: Unknown mcast interface: bcsh0
IPVS: Unknown mcast interface: bcsh0
IPVS: Unknown mcast interface: bcsh0
IPVS: Unknown mcast interface: bcsh0
IPVS: Unknown mcast interface: bcsh0
IPVS: Unknown mcast interface: bcsh0
IPVS: Unknown mcast interface: bcsh0
IPVS: Unknown mcast interface: bcsh0
IPVS: sync thread started: state = BACKUP, mcast_ifn = bcsh0, syncid = 0,  
id = 0
IPVS: Unknown mcast interface: bcsh0
IPVS: Unknown mcast interface: bcsh0
IPVS: Unknown mcast interface: bcsh0
IPVS: Unknown mcast interface: bcsh0
IPVS: Unknown mcast interface: bcsh0
IPVS: Unknown mcast interface: bcsh0
IPVS: Unknown mcast interface: bcsh0
IPVS: Unknown mcast interface: bcsh0

---
This bug is generated by a dumb bot. It may contain errors.
See https://goo.gl/tpsmEJ for details.
Direct all questions to [email-masked].

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