Subject: possible deadlock in rtnl_lock (6)

From: syzbot <[email-masked]>
Date: Mon, 08 Jul 2019 12:37:06 -0700

Hello,

syzbot found the following crash on:

HEAD commit:    537de0c8 ipv4: Fix NULL pointer dereference in ipv4_neigh_..
git tree:       net
console output: https://syzkaller.appspot.com/x/log.txt?x=14521cc3a00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=90f5d2d9c1e7421c
dashboard link: https://syzkaller.appspot.com/bug?extid=174ce29c2308dec5bc68
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1777debba00000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=16969b53a00000

The bug was bisected to:

commit 455302d1c9ae9318660aaeb9748a01ff414c9741
Author: Ilya Maximets <[email-masked]>
Date:   Fri Jun 28 08:04:07 2019 +0000

     xdp: fix hang while unregistering device bound to xdp socket

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=1179943da00000
final crash:    https://syzkaller.appspot.com/x/report.txt?x=1379943da00000
console output: https://syzkaller.appspot.com/x/log.txt?x=1579943da00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: [email-masked]
Fixes: 455302d1c9ae ("xdp: fix hang while unregistering device bound to xdp  
socket")

======================================================
WARNING: possible circular locking dependency detected
5.2.0-rc6+ #76 Not tainted
------------------------------------------------------
syz-executor613/9114 is trying to acquire lock:
000000002c564901 (rtnl_mutex){+.+.}, at: rtnl_lock+0x17/0x20  
net/core/rtnetlink.c:72

but task is already holding lock:
0000000039d6ee9b (&xs->mutex){+.+.}, at: xsk_bind+0x16a/0xe70  
net/xdp/xsk.c:422

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #2 (&xs->mutex){+.+.}:
        __mutex_lock_common kernel/locking/mutex.c:926 [inline]
        __mutex_lock+0xf7/0x1310 kernel/locking/mutex.c:1073
        mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:1088
        xsk_notifier+0x149/0x290 net/xdp/xsk.c:730
        notifier_call_chain+0xc2/0x230 kernel/notifier.c:95
        __raw_notifier_call_chain kernel/notifier.c:396 [inline]
        raw_notifier_call_chain+0x2e/0x40 kernel/notifier.c:403
        call_netdevice_notifiers_info+0x3f/0x90 net/core/dev.c:1749
        call_netdevice_notifiers_extack net/core/dev.c:1761 [inline]
        call_netdevice_notifiers net/core/dev.c:1775 [inline]
        rollback_registered_many+0x9b9/0xfc0 net/core/dev.c:8206
        rollback_registered+0x109/0x1d0 net/core/dev.c:8248
        unregister_netdevice_queue net/core/dev.c:9295 [inline]
        unregister_netdevice_queue+0x1ee/0x2c0 net/core/dev.c:9288
        br_dev_delete+0x145/0x1a0 net/bridge/br_if.c:383
        br_del_bridge+0xd7/0x120 net/bridge/br_if.c:483
        br_ioctl_deviceless_stub+0x2a4/0x7b0 net/bridge/br_ioctl.c:376
        sock_ioctl+0x44b/0x780 net/socket.c:1141
        vfs_ioctl fs/ioctl.c:46 [inline]
        file_ioctl fs/ioctl.c:509 [inline]
        do_vfs_ioctl+0xd5f/0x1380 fs/ioctl.c:696
        ksys_ioctl+0xab/0xd0 fs/ioctl.c:713
        __do_sys_ioctl fs/ioctl.c:720 [inline]
        __se_sys_ioctl fs/ioctl.c:718 [inline]
        __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:718
        do_syscall_64+0xfd/0x680 arch/x86/entry/common.c:301
        entry_SYSCALL_64_after_hwframe+0x49/0xbe

-> #1 (&net->xdp.lock){+.+.}:
        __mutex_lock_common kernel/locking/mutex.c:926 [inline]
        __mutex_lock+0xf7/0x1310 kernel/locking/mutex.c:1073
        mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:1088
        xsk_notifier+0xa7/0x290 net/xdp/xsk.c:726
        notifier_call_chain+0xc2/0x230 kernel/notifier.c:95
        __raw_notifier_call_chain kernel/notifier.c:396 [inline]
        raw_notifier_call_chain+0x2e/0x40 kernel/notifier.c:403
        call_netdevice_notifiers_info+0x3f/0x90 net/core/dev.c:1749
        call_netdevice_notifiers_extack net/core/dev.c:1761 [inline]
        call_netdevice_notifiers net/core/dev.c:1775 [inline]
        rollback_registered_many+0x9b9/0xfc0 net/core/dev.c:8206
        rollback_registered+0x109/0x1d0 net/core/dev.c:8248
        unregister_netdevice_queue net/core/dev.c:9295 [inline]
        unregister_netdevice_queue+0x1ee/0x2c0 net/core/dev.c:9288
        br_dev_delete+0x145/0x1a0 net/bridge/br_if.c:383
        br_del_bridge+0xd7/0x120 net/bridge/br_if.c:483
        br_ioctl_deviceless_stub+0x2a4/0x7b0 net/bridge/br_ioctl.c:376
        sock_ioctl+0x44b/0x780 net/socket.c:1141
        vfs_ioctl fs/ioctl.c:46 [inline]
        file_ioctl fs/ioctl.c:509 [inline]
        do_vfs_ioctl+0xd5f/0x1380 fs/ioctl.c:696
        ksys_ioctl+0xab/0xd0 fs/ioctl.c:713
        __do_sys_ioctl fs/ioctl.c:720 [inline]
        __se_sys_ioctl fs/ioctl.c:718 [inline]
        __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:718
        do_syscall_64+0xfd/0x680 arch/x86/entry/common.c:301
        entry_SYSCALL_64_after_hwframe+0x49/0xbe

-> #0 (rtnl_mutex){+.+.}:
        lock_acquire+0x16f/0x3f0 kernel/locking/lockdep.c:4303
        __mutex_lock_common kernel/locking/mutex.c:926 [inline]
        __mutex_lock+0xf7/0x1310 kernel/locking/mutex.c:1073
        mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:1088
        rtnl_lock+0x17/0x20 net/core/rtnetlink.c:72
        xdp_umem_assign_dev+0xbe/0x8b0 net/xdp/xdp_umem.c:96
        xsk_bind+0x4d7/0xe70 net/xdp/xsk.c:488
        __sys_bind+0x239/0x290 net/socket.c:1653
        __do_sys_bind net/socket.c:1664 [inline]
        __se_sys_bind net/socket.c:1662 [inline]
        __x64_sys_bind+0x73/0xb0 net/socket.c:1662
        do_syscall_64+0xfd/0x680 arch/x86/entry/common.c:301
        entry_SYSCALL_64_after_hwframe+0x49/0xbe

other info that might help us debug this:

Chain exists of:
   rtnl_mutex --> &net->xdp.lock --> &xs->mutex

  Possible unsafe locking scenario:

        CPU0                    CPU1
        ----                    ----
   lock(&xs->mutex);
                                lock(&net->xdp.lock);
                                lock(&xs->mutex);
   lock(rtnl_mutex);

  *** DEADLOCK ***

1 lock held by syz-executor613/9114:
  #0: 0000000039d6ee9b (&xs->mutex){+.+.}, at: xsk_bind+0x16a/0xe70  
net/xdp/xsk.c:422

stack backtrace:
CPU: 1 PID: 9114 Comm: syz-executor613 Not tainted 5.2.0-rc6+ #76
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.cold+0x1cc/0x28f kernel/locking/lockdep.c:1565
  check_prev_add kernel/locking/lockdep.c:2310 [inline]
  check_prevs_add kernel/locking/lockdep.c:2418 [inline]
  validate_chain kernel/locking/lockdep.c:2800 [inline]
  __lock_acquire+0x3755/0x5490 kernel/locking/lockdep.c:3793
  lock_acquire+0x16f/0x3f0 kernel/locking/lockdep.c:4303
  __mutex_lock_common kernel/locking/mutex.c:926 [inline]
  __mutex_lock+0xf7/0x1310 kernel/locking/mutex.c:1073
  mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:1088
  rtnl_lock+0x17/0x20 net/core/rtnetlink.c:72
  xdp_umem_assign_dev+0xbe/0x8b0 net/xdp/xdp_umem.c:96
  xsk_bind+0x4d7/0xe70 net/xdp/xsk.c:488
  __sys_bind+0x239/0x290 net/socket.c:1653
  __do_sys_bind net/socket.c:1664 [inline]
  __se_sys_bind net/socket.c:1662 [inline]
  __x64_sys_bind+0x73/0xb0 net/socket.c:1662
  do_syscall_64+0xfd/0x680 arch/x86/entry/common.c:301
  entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x447909
Code: e8 cc e7 ff ff 48 83 c4 18 c3 0f 1f 80 00 00 00 00 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 3b 08 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007fb2a478fd98 EFLAGS: 00000246 ORIG_RAX: 0000000000000031
RAX: ffffffffffffffda RBX: 00000000006dcc58 RCX: 0000000000447909
RDX: 0000000000000010 RSI: 0000000020000040 RDI: 0000000000000005
RBP: 00000000006dcc50 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000006dcc5c
R13: 0000003066736362 R14: 0000000000000000 R15: 0000003066736362

---
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