WARNING: refcount bug in __sk_destruct

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    fd786fb1 net: convert suitable drivers to use phy_do_ioctl..
git tree:       net-next
console output: https://syzkaller.appspot.com/x/log.txt?x=14e9726ee00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=7f93900a7904130d
dashboard link: https://syzkaller.appspot.com/bug?extid=dd803bc0e8adf0003261
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=12af9369e00000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=10583d76e00000

The bug was bisected to:

commit 14215108a1fd7e002c0a1f9faf8fbaf41fdda50d
Author: Cong Wang <xiyou.wangcong@xxxxxxxxx>
Date:   Thu Feb 21 05:37:42 2019 +0000

    net_sched: initialize net pointer inside tcf_exts_init()

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=175b66bee00000
final crash:    https://syzkaller.appspot.com/x/report.txt?x=14db66bee00000
console output: https://syzkaller.appspot.com/x/log.txt?x=10db66bee00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+dd803bc0e8adf0003261@xxxxxxxxxxxxxxxxxxxxxxxxx
Fixes: 14215108a1fd ("net_sched: initialize net pointer inside tcf_exts_init()")

RBP: 0000000000000000 R08: 0000000000000002 R09: 00000000bb1414ac
R10: 0000000000000000 R11: 0000000000000246 R12: ffffffffffffffff
R13: 0000000000000009 R14: 0000000000000000 R15: 0000000000000000
------------[ cut here ]------------
refcount_t: underflow; use-after-free.
WARNING: CPU: 1 PID: 9577 at lib/refcount.c:28 refcount_warn_saturate+0x1dc/0x1f0 lib/refcount.c:28
Kernel panic - not syncing: panic_on_warn set ...
CPU: 1 PID: 9577 Comm: syz-executor327 Not tainted 5.5.0-rc6-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+0x1dc/0x1f0 lib/refcount.c:28
Code: e9 d8 fe ff ff 48 89 df e8 c1 f8 16 fe e9 85 fe ff ff e8 a7 77 d8 fd 48 c7 c7 e0 44 71 88 c6 05 9e 86 db 06 01 e8 93 27 a9 fd <0f> 0b e9 ac fe ff ff 0f 1f 00 66 2e 0f 1f 84 00 00 00 00 00 55 48
RSP: 0018:ffffc9000c067b00 EFLAGS: 00010282
RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffffff815e5dd6 RDI: fffff5200180cf52
RBP: ffffc9000c067b10 R08: ffff8880a8630340 R09: ffffed1015d26621
R10: ffffed1015d26620 R11: ffff8880ae933107 R12: 0000000000000003
R13: ffff888090256000 R14: ffff8880a7e5c040 R15: ffff8880a7e5c044
 refcount_sub_and_test include/linux/refcount.h:261 [inline]
 refcount_dec_and_test include/linux/refcount.h:281 [inline]
 put_net include/net/net_namespace.h:259 [inline]
 __sk_destruct+0x6d8/0x7f0 net/core/sock.c:1723
 sk_destruct+0xd5/0x110 net/core/sock.c:1739
 __sk_free+0xfb/0x3f0 net/core/sock.c:1750
 sk_free+0x83/0xb0 net/core/sock.c:1761
 sock_put include/net/sock.h:1719 [inline]
 __tun_detach+0xbe0/0x1150 drivers/net/tun.c:728
 tun_detach drivers/net/tun.c:740 [inline]
 tun_chr_close+0xe0/0x180 drivers/net/tun.c:3455
 __fput+0x2ff/0x890 fs/file_table.c:280
 ____fput+0x16/0x20 fs/file_table.c:313
 task_work_run+0x145/0x1c0 kernel/task_work.c:113
 exit_task_work include/linux/task_work.h:22 [inline]
 do_exit+0xba9/0x2f50 kernel/exit.c:801
 do_group_exit+0x135/0x360 kernel/exit.c:899
 __do_sys_exit_group kernel/exit.c:910 [inline]
 __se_sys_exit_group kernel/exit.c:908 [inline]
 __x64_sys_exit_group+0x44/0x50 kernel/exit.c:908
 do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x441a48
Code: Bad RIP value.
RSP: 002b:00007fffe55809a8 EFLAGS: 00000246 ORIG_RAX: 00000000000000e7
RAX: ffffffffffffffda RBX: 0000000000000001 RCX: 0000000000441a48
RDX: 0000000000000001 RSI: 000000000000003c RDI: 0000000000000001
RBP: 00000000004c8430 R08: 00000000000000e7 R09: ffffffffffffffd0
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000001
R13: 00000000006dba80 R14: 0000000000000000 R15: 0000000000000000
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@xxxxxxxxxxxxxxxxx

syzbot will keep track of this bug report. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
For information about bisection process see: https://goo.gl/tpsmEJ#bisection
syzbot can test patches for this bug, for details see:
https://goo.gl/tpsmEJ#testing-patches