WARNING: refcount bug in tcp_twsk_unique

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 1236568ee3cb Merge tag 'gpio-v4.18-3' of git://git.kernel...
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1145beac400000
kernel config: https://syzkaller.appspot.com/x/.config?x=152cb8ccd35b1f70
dashboard link: https://syzkaller.appspot.com/bug?extid=34e548f2b857a2f8025c
compiler: gcc (GCC) 8.0.1 20180413 (experimental)
CC: [da...@davemloft.net edum...@google.com
kuz...@ms2.inr.ac.ru linux-...@vger.kernel.org net...@vger.kernel.org
yosh...@linux-ipv6.org]

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+34e548...@syzkaller.appspotmail.com

kernel msg: ebtables bug: please report to author: Couldn't copy entries
from userspace
------------[ cut here ]------------
refcount_t: increment on 0; use-after-free.
WARNING: CPU: 1 PID: 22861 at lib/refcount.c:153 refcount_inc+0x5d/0x70
lib/refcount.c:153
Kernel panic - not syncing: panic_on_warn set ...

CPU: 1 PID: 22861 Comm: syz-executor3 Not tainted 4.18.0-rc8+ #180
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+0x1c9/0x2b4 lib/dump_stack.c:113
panic+0x238/0x4e7 kernel/panic.c:184
__warn.cold.8+0x163/0x1ba kernel/panic.c:536
report_bug+0x252/0x2d0 lib/bug.c:186
fixup_bug arch/x86/kernel/traps.c:178 [inline]
do_error_trap+0x1fc/0x4d0 arch/x86/kernel/traps.c:296
do_invalid_op+0x1b/0x20 arch/x86/kernel/traps.c:316
invalid_op+0x14/0x20 arch/x86/entry/entry_64.S:992
RIP: 0010:refcount_inc+0x5d/0x70 lib/refcount.c:153
Code: 1d 4d ef 25 05 31 ff 89 de e8 7f b0 1c fe 84 db 75 df e8 a6 af 1c fe
48 c7 c7 40 4b 3a 87 c6 05 2d ef 25 05 01 e8 83 c8 e7 fd <0f> 0b eb c3 0f
1f 44 00 00 66 2e 0f 1f 84 00 00 00 00 00 55 48 89
RSP: 0018:ffff8801cac2ee00 EFLAGS: 00010282
RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffffc90005638000
RDX: 000000000000347e RSI: ffffffff81632481 RDI: ffff8801cac2ead8
RBP: ffff8801cac2ee08 R08: ffff8801ca27c280 R09: 0000000000000002
R10: ffff8801ca27c280 R11: 0000000000000000 R12: ffff8801c5ea8e40
R13: 000000005b6a4e51 R14: 000000005b6a4e51 R15: ffff8801d787bf50
sock_hold include/net/sock.h:627 [inline]
tcp_twsk_unique+0x6a5/0x7f0 net/ipv4/tcp_ipv4.c:177
twsk_unique include/net/timewait_sock.h:30 [inline]
__inet6_check_established+0x757/0x1210 net/ipv6/inet6_hashtables.c:274
__inet_hash_connect+0x363/0xfc0 net/ipv4/inet_hashtables.c:686
inet6_hash_connect+0x76/0xe0 net/ipv6/inet6_hashtables.c:325
tcp_v6_connect+0x1838/0x2970 net/ipv6/tcp_ipv6.c:299
__inet_stream_connect+0x964/0x1150 net/ipv4/af_inet.c:655
tcp_sendmsg_fastopen net/ipv4/tcp.c:1162 [inline]
tcp_sendmsg_locked+0x2842/0x3e80 net/ipv4/tcp.c:1209
tcp_sendmsg+0x2f/0x50 net/ipv4/tcp.c:1447
inet_sendmsg+0x1a1/0x690 net/ipv4/af_inet.c:798
sock_sendmsg_nosec net/socket.c:642 [inline]
sock_sendmsg+0xd5/0x120 net/socket.c:652
__sys_sendto+0x3d7/0x670 net/socket.c:1798
__do_sys_sendto net/socket.c:1810 [inline]
__se_sys_sendto net/socket.c:1806 [inline]
__x64_sys_sendto+0xe1/0x1a0 net/socket.c:1806
do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x456cb9
Code: fd b4 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 cb b4 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007fe2db54fc78 EFLAGS: 00000246 ORIG_RAX: 000000000000002c
RAX: ffffffffffffffda RBX: 00007fe2db5506d4 RCX: 0000000000456cb9
RDX: 0000000000000000 RSI: 0000000020000080 RDI: 0000000000000017
RBP: 00000000009300a0 R08: 0000000020000040 R09: 000000000000001c
R10: 0000000020000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 00000000004d38a0 R14: 00000000004c852f R15: 0000000000000000
Dumping ftrace buffer:
(ftrace buffer empty)
Kernel Offset: disabled
Rebooting in 86400 seconds..


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[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.