WARNING: refcount bug in j1939_netdev_start

WARNING: refcount bug in j1939_netdev_start

[syzbot]

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..


---
This bug is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzkaller@googlegroups.com.

syzbot will keep track of this bug report. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

Re: WARNING: refcount bug in j1939_netdev_start

[syzbot]

syzbot has found a reproducer for the following crash on:

HEAD commit:    9805a683 Merge branch 'x86-urgent-for-linus' of git://git...
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=133de01ce00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=896c87b73c6fcda6
dashboard link: https://syzkaller.appspot.com/bug?extid=afd421337a736d6c1ee6
compiler:       clang version 9.0.0 (/home/glider/llvm/clang  
80fee25776c2fb61e74c1ecb1a523375c2500b69)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=10d713c6e00000

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: 1 PID: 8514 at lib/refcount.c:156  
refcount_inc_checked+0x4b/0x50 lib/refcount.c:156
Kernel panic - not syncing: panic_on_warn set ...
CPU: 1 PID: 8514 Comm: syz-executor.3 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+0x1fb/0x318 lib/dump_stack.c:118
  panic+0x264/0x7a9 kernel/panic.c:221
  __warn+0x20e/0x210 kernel/panic.c:582
  report_bug+0x1b6/0x2f0 lib/bug.c:195
  fixup_bug arch/x86/kernel/traps.c:179 [inline]
  do_error_trap+0xd7/0x440 arch/x86/kernel/traps.c:272
  do_invalid_op+0x36/0x40 arch/x86/kernel/traps.c:291
  invalid_op+0x23/0x30 arch/x86/entry/entry_64.S:1028
RIP: 0010:refcount_inc_checked+0x4b/0x50 lib/refcount.c:156
Code: 3d f7 ab 75 05 01 75 08 e8 12 e2 2d fe 5b 5d c3 e8 0a e2 2d fe c6 05  
e1 ab 75 05 01 48 c7 c7 b4 c5 40 88 31 c0 e8 a5 78 00 fe <0f> 0b eb df 90  
55 48 89 e5 41 57 41 56 41 55 41 54 53 48 83 ec 10
RSP: 0018:ffff8880816dfd10 EFLAGS: 00010246
RAX: 8358cd98639ffe00 RBX: ffff8880975b50f0 RCX: ffff8880a4010540
RDX: 0000000000000000 RSI: 0000000080000000 RDI: 0000000000000000
RBP: ffff8880816dfd18 R08: ffffffff815ca054 R09: ffffed1015d640d2
R10: ffffed1015d640d2 R11: 0000000000000000 R12: ffff88808e820588
R13: dffffc0000000000 R14: ffff88808e820000 R15: 1ffff11011d04047
  j1939_netdev_start+0x47c/0x730 net/can/j1939/main.c:267
  j1939_sk_bind+0x2c0/0xac0 net/can/j1939/socket.c:438
  __sys_bind+0x2c2/0x3a0 net/socket.c:1647
  __do_sys_bind net/socket.c:1658 [inline]
  __se_sys_bind net/socket.c:1656 [inline]
  __x64_sys_bind+0x7a/0x90 net/socket.c:1656
  do_syscall_64+0xf7/0x1c0 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:00007efc734cbc78 EFLAGS: 00000246 ORIG_RAX: 0000000000000031
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 000000000045a219
RDX: 0000000000000018 RSI: 0000000020000240 RDI: 0000000000000005
RBP: 000000000075c070 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007efc734cc6d4
R13: 00000000004c057e R14: 00000000004d2c50 R15: 00000000ffffffff
Kernel Offset: disabled
Rebooting in 86400 seconds..

Re: WARNING: refcount bug in j1939_netdev_start

[syzbot]

syzbot has bisected this bug to:

commit 9d71dd0c70099914fcd063135da3c580865e924c
Author: The j1939 authors <linux-can@vger.kernel.org>
Date:   Mon Oct 8 09:48:36 2018 +0000

     can: add support of SAE J1939 protocol

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=17100f3ae00000
start commit:   9805a683 Merge branch 'x86-urgent-for-linus' of git://git...
git tree:       upstream
final crash:    https://syzkaller.appspot.com/x/report.txt?x=14900f3ae00000
console output: https://syzkaller.appspot.com/x/log.txt?x=10900f3ae00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=896c87b73c6fcda6
dashboard link: https://syzkaller.appspot.com/bug?extid=afd421337a736d6c1ee6
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=10d713c6e00000

Reported-by: syzbot+afd421337a736d6c1ee6@syzkaller.appspotmail.com
Fixes: 9d71dd0c7009 ("can: add support of SAE J1939 protocol")

For information about bisection process see: https://goo.gl/tpsmEJ#bisection