refcount_t: underflow; use-after-free.
------------[ cut here ]------------
WARNING: CPU: 0 PID: 8413 at net/ipv4/af_inet.c:154 inet_sock_destruct+0x729/0x950 net/ipv4/af_inet.c:154
Kernel panic - not syncing: panic_on_warn set ...

CPU: 0 PID: 8413 Comm: syz-executor0 Not tainted 4.13.0+ #42
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:16 [inline]
 dump_stack+0x194/0x257 lib/dump_stack.c:52
 panic+0x1e4/0x417 kernel/panic.c:181
 __warn+0x1c4/0x1d9 kernel/panic.c:542
 report_bug+0x211/0x2d0 lib/bug.c:183
 fixup_bug+0x40/0x90 arch/x86/kernel/traps.c:178
 do_trap_no_signal arch/x86/kernel/traps.c:212 [inline]
 do_trap+0x260/0x390 arch/x86/kernel/traps.c:261
 do_error_trap+0x120/0x390 arch/x86/kernel/traps.c:298
 do_invalid_op+0x1b/0x20 arch/x86/kernel/traps.c:311
 invalid_op+0x18/0x20 arch/x86/entry/entry_64.S:905
RIP: 0010:inet_sock_destruct+0x729/0x950 net/ipv4/af_inet.c:154
RSP: 0018:ffff8801c0057158 EFLAGS: 00010216
RAX: 0000000000010000 RBX: ffff8801ce1e5800 RCX: ffffc9000199b000
RDX: 00000000000009f7 RSI: ffffffff84146479 RDI: ffff8801ce1e5a60
RBP: ffff8801c0057280 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 1ffff1003800ae3b
R13: 0000000000000000 R14: ffffffff84790cb0 R15: ffff8801ce1e5950
 sctp_destruct_sock+0x43/0x50 net/sctp/socket.c:4436
 __sk_destruct+0xfd/0x910 net/core/sock.c:1560
 sk_destruct+0x47/0x80 net/core/sock.c:1595
 __sk_free+0x57/0x230 net/core/sock.c:1603
 sk_free+0x2a/0x40 net/core/sock.c:1614
 sock_put include/net/sock.h:1649 [inline]
 sctp_close+0x487/0x980 net/sctp/socket.c:1559
 inet_release+0xed/0x1c0 net/ipv4/af_inet.c:425
 sock_release+0x8d/0x1e0 net/socket.c:597
 sock_close+0x16/0x20 net/socket.c:1126
 __fput+0x333/0x7f0 fs/file_table.c:210
 ____fput+0x15/0x20 fs/file_table.c:246
 task_work_run+0x199/0x270 kernel/task_work.c:112
 get_signal+0x1440/0x17e0 kernel/signal.c:2164
 do_signal+0x94/0x1ee0 arch/x86/kernel/signal.c:808
 exit_to_usermode_loop+0x224/0x300 arch/x86/entry/common.c:158
 prepare_exit_to_usermode arch/x86/entry/common.c:197 [inline]
 syscall_return_slowpath+0x42f/0x500 arch/x86/entry/common.c:266
 entry_SYSCALL_64_fastpath+0xbc/0xbe
RIP: 0033:0x451e59
RSP: 002b:00007f1567f60c08 EFLAGS: 00000216 ORIG_RAX: 000000000000002b
RAX: fffffffffffffff2 RBX: 00000000007182c0 RCX: 0000000000451e59
RDX: 0000000020b51ffc RSI: 0000000020b52000 RDI: 0000000000000019
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000216 R12: 00000000004b6e93
R13: 00000000ffffffff R14: 0000000000000019 R15: 0000000020b52000
Dumping ftrace buffer:
   (ftrace buffer empty)
Kernel Offset: disabled
Rebooting in 86400 seconds..