Subject: WARNING: refcount bug in nr_release

From: syzbot <[email-masked]>
Date: Mon, 07 Jan 2019 01:53:03 -0800

Hello,

syzbot found the following crash on:

HEAD commit:    f1c2f8857c5a Merge tag 'powerpc-4.21-2' of git://git.kerne..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=16af96bb400000
kernel config:  https://syzkaller.appspot.com/x/.config?x=47c29c309c47af16
dashboard link: https://syzkaller.appspot.com/bug?extid=b0b1952f5864b4009b09
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: [email-masked]

------------[ cut here ]------------
refcount_t: increment on 0; use-after-free.
WARNING: CPU: 1 PID: 3768 at lib/refcount.c:153 refcount_inc_checked  
lib/refcount.c:153 [inline]
WARNING: CPU: 1 PID: 3768 at lib/refcount.c:153  
refcount_inc_checked+0x61/0x70 lib/refcount.c:151
Kernel panic - not syncing: panic_on_warn set ...
CPU: 1 PID: 3768 Comm: syz-executor5 Not tainted 4.20.0+ #11
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+0x1db/0x2d0 lib/dump_stack.c:113
  panic+0x2cb/0x65c kernel/panic.c:214
  __warn.cold+0x20/0x48 kernel/panic.c:571
  report_bug+0x263/0x2b0 lib/bug.c:186
  fixup_bug arch/x86/kernel/traps.c:178 [inline]
  fixup_bug arch/x86/kernel/traps.c:173 [inline]
  do_error_trap+0x11b/0x200 arch/x86/kernel/traps.c:271
  do_invalid_op+0x37/0x50 arch/x86/kernel/traps.c:290
  invalid_op+0x14/0x20 arch/x86/entry/entry_64.S:973
RIP: 0010:refcount_inc_checked lib/refcount.c:153 [inline]
RIP: 0010:refcount_inc_checked+0x61/0x70 lib/refcount.c:151
Code: 1d ec 29 c8 06 31 ff 89 de e8 fb 1a f2 fd 84 db 75 dd e8 b2 19 f2 fd  
48 c7 c7 e0 98 81 88 c6 05 cc 29 c8 06 01 e8 df 6e bb fd <0f> 0b eb c1 90  
66 2e 0f 1f 84 00 00 00 00 00 55 48 89 e5 41 54 49
RSP: 0018:ffff8880675af460 EFLAGS: 00010282
RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffffff81684ce6 RDI: 0000000000000005
RBP: ffff8880675af470 R08: ffff88806164e600 R09: ffffed1015ce5021
R10: ffffed1015ce5020 R11: ffff8880ae728107 R12: ffff88808cf2a940
R13: ffff88809669c1a0 R14: ffff88808cf2ac28 R15: ffff88808cf2a940
  sock_hold include/net/sock.h:647 [inline]
  nr_release+0x62/0x3c0 net/netrom/af_netrom.c:523
  __sock_release+0xd3/0x250 net/socket.c:579
  sock_close+0x1b/0x30 net/socket.c:1141
  __fput+0x3c5/0xb10 fs/file_table.c:278
  ____fput+0x16/0x20 fs/file_table.c:309
  task_work_run+0x1f4/0x2b0 kernel/task_work.c:113
  exit_task_work include/linux/task_work.h:22 [inline]
  do_exit+0x19d6/0x2650 kernel/exit.c:867
  do_group_exit+0x177/0x430 kernel/exit.c:970
  get_signal+0x8b4/0x19b0 kernel/signal.c:2517
  do_signal+0x91/0x1ea0 arch/x86/kernel/signal.c:816
  exit_to_usermode_loop+0x2f7/0x3b0 arch/x86/entry/common.c:162
  prepare_exit_to_usermode arch/x86/entry/common.c:197 [inline]
  syscall_return_slowpath arch/x86/entry/common.c:268 [inline]
  do_syscall_64+0x696/0x800 arch/x86/entry/common.c:293
  entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x457ec9
Code: 6d b7 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 3b b7 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007fb2e6be7cf8 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca
RAX: fffffffffffffe00 RBX: 000000000073c048 RCX: 0000000000457ec9
RDX: 0000000000000000 RSI: 0000000000000080 RDI: 000000000073c048
RBP: 000000000073c040 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 000000000073c04c
R13: 00007fffae482f5f R14: 00007fb2e6be89c0 R15: 000000000073c04c
Kernel Offset: disabled
Rebooting in 86400 seconds..

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