WARNING: refcount bug in j1939_netdev_start (2)

[syzbot <syzbot+85d9878b19c94f9019ad@syzkaller.appspotmail.com>]

Hello,

syzbot found the following crash on:

HEAD commit:    6327edce Merge branch 'i2c/for-current' of git://git.kerne..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1608b349e00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=7e89bd00623fe71e
dashboard link: https://syzkaller.appspot.com/bug?extid=85d9878b19c94f9019ad
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+85d9878b19c94f9019ad@syzkaller.appspotmail.com

------------[ cut here ]------------
refcount_t: addition on 0; use-after-free.
WARNING: CPU: 1 PID: 26973 at lib/refcount.c:25  
refcount_warn_saturate+0x174/0x1f0 lib/refcount.c:25
Kernel panic - not syncing: panic_on_warn set ...
CPU: 1 PID: 26973 Comm: syz-executor.2 Not tainted 5.5.0-rc5-syzkaller #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+0x197/0x210 lib/dump_stack.c:118
  panic+0x2e3/0x75c kernel/panic.c:221
  __warn.cold+0x2f/0x3e kernel/panic.c:582
  report_bug+0x289/0x300 lib/bug.c:195
  fixup_bug arch/x86/kernel/traps.c:174 [inline]
  fixup_bug arch/x86/kernel/traps.c:169 [inline]
  do_error_trap+0x11b/0x200 arch/x86/kernel/traps.c:267
  do_invalid_op+0x37/0x50 arch/x86/kernel/traps.c:286
  invalid_op+0x23/0x30 arch/x86/entry/entry_64.S:1027
RIP: 0010:refcount_warn_saturate+0x174/0x1f0 lib/refcount.c:25
Code: 06 31 ff 89 de e8 6c 18 d9 fd 84 db 0f 85 33 ff ff ff e8 1f 17 d9 fd  
48 c7 c7 c0 27 71 88 c6 05 7b d8 da 06 01 e8 9b c6 a9 fd <0f> 0b e9 14 ff  
ff ff e8 00 17 d9 fd 0f b6 1d 60 d8 da 06 31 ff 89
RSP: 0018:ffffc90008e77ce0 EFLAGS: 00010286
RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
RDX: 0000000000009ee4 RSI: ffffffff815e53a6 RDI: fffff520011cef8e
RBP: ffffc90008e77cf0 R08: ffff888093580600 R09: ffffed1015d26621
R10: ffffed1015d26620 R11: ffff8880ae933107 R12: 0000000000000002
R13: ffff888047150000 R14: ffff8880a725b000 R15: 0000000000000118
  refcount_add include/linux/refcount.h:191 [inline]
  refcount_inc include/linux/refcount.h:228 [inline]
  kref_get include/linux/kref.h:45 [inline]
  j1939_netdev_start+0x534/0x650 net/can/j1939/main.c:277
  j1939_sk_bind+0x68d/0x980 net/can/j1939/socket.c:469
  __sys_bind+0x239/0x290 net/socket.c:1649
  __do_sys_bind net/socket.c:1660 [inline]
  __se_sys_bind net/socket.c:1658 [inline]
  __x64_sys_bind+0x73/0xb0 net/socket.c:1658
  do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
  entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x45af49
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:00007f0a1184dc78 EFLAGS: 00000246 ORIG_RAX: 0000000000000031
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 000000000045af49
RDX: 0000000000000018 RSI: 0000000020000240 RDI: 0000000000000005
RBP: 000000000075c070 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f0a1184e6d4
R13: 00000000004c1358 R14: 00000000004d6080 R15: 00000000ffffffff
Kernel Offset: disabled
Rebooting in 86400 seconds..


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