WARNING: refcount bug in j1939_netdev_start

[syzbot <syzbot+afd421337a736d6c1ee6@syzkaller.appspotmail.com>]

Hello,

syzbot found the following crash on:

HEAD commit:    a99d8080 Linux 5.4-rc6
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=11a7443ae00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=8c5e2eca3f31f9bf
dashboard link: https://syzkaller.appspot.com/bug?extid=afd421337a736d6c1ee6
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)

Unfortunately, I don't have any reproducer for this crash yet.

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+afd421337a736d6c1ee6@syzkaller.appspotmail.com

------------[ cut here ]------------
refcount_t: increment on 0; use-after-free.
WARNING: CPU: 0 PID: 27509 at lib/refcount.c:156 refcount_inc_checked  
lib/refcount.c:156 [inline]
WARNING: CPU: 0 PID: 27509 at lib/refcount.c:156  
refcount_inc_checked+0x61/0x70 lib/refcount.c:154
Kernel panic - not syncing: panic_on_warn set ...
CPU: 0 PID: 27509 Comm: syz-executor.5 Not tainted 5.4.0-rc6 #0
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
  panic+0x2e3/0x75c kernel/panic.c:221
  __warn.cold+0x2f/0x35 kernel/panic.c:582
  report_bug+0x289/0x300 lib/bug.c:195
  fixup_bug arch/x86/kernel/traps.c:179 [inline]
  fixup_bug arch/x86/kernel/traps.c:174 [inline]
  do_error_trap+0x11b/0x200 arch/x86/kernel/traps.c:272
  do_invalid_op+0x37/0x50 arch/x86/kernel/traps.c:291
  invalid_op+0x23/0x30 arch/x86/entry/entry_64.S:1028
RIP: 0010:refcount_inc_checked lib/refcount.c:156 [inline]
RIP: 0010:refcount_inc_checked+0x61/0x70 lib/refcount.c:154
Code: 1d ce 0c 7e 06 31 ff 89 de e8 bb a8 2e fe 84 db 75 dd e8 72 a7 2e fe  
48 c7 c7 c0 af e6 87 c6 05 ae 0c 7e 06 01 e8 57 dc ff fd <0f> 0b eb c1 90  
90 90 90 90 90 90 90 90 90 90 55 48 89 e5 41 57 41
RSP: 0018:ffff88805c33fce8 EFLAGS: 00010282
RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
RDX: 0000000000016597 RSI: ffffffff815cc396 RDI: ffffed100b867f8f
RBP: ffff88805c33fcf8 R08: ffff8880921ae440 R09: ffffed1015d04101
R10: ffffed1015d04100 R11: ffff8880ae820807 R12: ffff8880604010f0
R13: ffff88805c33fe00 R14: ffff888045255580 R15: 0000000000000118
  kref_get include/linux/kref.h:45 [inline]
  j1939_netdev_start+0x53/0x550 net/can/j1939/main.c:247
  j1939_sk_bind+0x65a/0x8e0 net/can/j1939/socket.c:438
  __sys_bind+0x239/0x290 net/socket.c:1647
  __do_sys_bind net/socket.c:1658 [inline]
  __se_sys_bind net/socket.c:1656 [inline]
  __x64_sys_bind+0x73/0xb0 net/socket.c:1656
  do_syscall_64+0xfa/0x760 arch/x86/entry/common.c:290
  entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x45a219
Code: ad b6 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 b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f2ba4d29c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000031
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 000000000045a219
RDX: 0000000000000018 RSI: 0000000020000240 RDI: 0000000000000003
RBP: 000000000075bfc8 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f2ba4d2a6d4
R13: 00000000004c057e R14: 00000000004d2c50 R15: 00000000ffffffff
Kernel Offset: disabled
Rebooting in 86400 seconds..


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