------------[ cut here ]------------
refcount_t: underflow; use-after-free.
WARNING: CPU: 0 PID: 9663 at lib/refcount.c:187 refcount_sub_and_test+0x167/0x1b0 lib/refcount.c:187
Kernel panic - not syncing: panic_on_warn set ...

CPU: 0 PID: 9663 Comm: syz-executor4 Not tainted 4.15.0-rc9+ #278
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:17 [inline]
 dump_stack+0x194/0x257 lib/dump_stack.c:53
 panic+0x1e4/0x41c kernel/panic.c:183
 __warn+0x1dc/0x200 kernel/panic.c:547
 report_bug+0x211/0x2d0 lib/bug.c:184
 fixup_bug.part.11+0x37/0x80 arch/x86/kernel/traps.c:178
 fixup_bug arch/x86/kernel/traps.c:247 [inline]
 do_error_trap+0x2d7/0x3e0 arch/x86/kernel/traps.c:296
 do_invalid_op+0x1b/0x20 arch/x86/kernel/traps.c:315
 invalid_op+0x22/0x40 arch/x86/entry/entry_64.S:1096
RIP: 0010:refcount_sub_and_test+0x167/0x1b0 lib/refcount.c:187
RSP: 0018:ffff8801c3bf63e0 EFLAGS: 00010282
RAX: dffffc0000000008 RBX: 0000000000000201 RCX: ffffffff8159ebae
RDX: 0000000000000000 RSI: 1ffff1003877ec37 RDI: ffff8801c3bf60e8
RBP: ffff8801c3bf6470 R08: 1ffff1003877ebf9 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 1ffff1003877ec7d
R13: 00000000fffffd01 R14: 0000000000000500 R15: ffff8801bd9ce23c
 sock_wfree+0xa6/0x140 net/core/sock.c:1812
 sctp_wfree+0x2a6/0x620 net/sctp/socket.c:7996
 skb_release_head_state+0x124/0x260 net/core/skbuff.c:612
 skb_release_all+0x15/0x60 net/core/skbuff.c:625
 __kfree_skb net/core/skbuff.c:641 [inline]
 consume_skb+0x153/0x490 net/core/skbuff.c:701
 sctp_chunk_destroy net/sctp/sm_make_chunk.c:1437 [inline]
 sctp_chunk_put+0x29c/0x420 net/sctp/sm_make_chunk.c:1464
 sctp_datamsg_destroy net/sctp/chunk.c:130 [inline]
 sctp_datamsg_put+0x22d/0x560 net/sctp/chunk.c:147
 sctp_chunk_free+0x46/0x60 net/sctp/sm_make_chunk.c:1449
 __sctp_outq_teardown+0xa5b/0x1230 net/sctp/outqueue.c:273
 sctp_outq_free+0x15/0x20 net/sctp/outqueue.c:293
 sctp_association_free+0x2d0/0x930 net/sctp/associola.c:356
 sctp_cmd_delete_tcb net/sctp/sm_sideeffect.c:939 [inline]
 sctp_cmd_interpreter net/sctp/sm_sideeffect.c:1355 [inline]
 sctp_side_effects net/sctp/sm_sideeffect.c:1222 [inline]
 sctp_do_sm+0x271b/0x6a20 net/sctp/sm_sideeffect.c:1193
 sctp_primitive_ABORT+0xa0/0xd0 net/sctp/primitive.c:119
 sctp_close+0x28b/0x980 net/sctp/socket.c:1559
 inet_release+0xed/0x1c0 net/ipv4/af_inet.c:426
 sock_release+0x8d/0x1e0 net/socket.c:602
 sock_close+0x16/0x20 net/socket.c:1131
 __fput+0x327/0x7e0 fs/file_table.c:210
 ____fput+0x15/0x20 fs/file_table.c:244
 task_work_run+0x199/0x270 kernel/task_work.c:113
 exit_task_work include/linux/task_work.h:22 [inline]
 do_exit+0x9bb/0x1ad0 kernel/exit.c:865
 do_group_exit+0x149/0x400 kernel/exit.c:968
 get_signal+0x73f/0x16c0 kernel/signal.c:2335
 do_signal+0x90/0x1eb0 arch/x86/kernel/signal.c:809
 exit_to_usermode_loop+0x214/0x310 arch/x86/entry/common.c:158
 prepare_exit_to_usermode arch/x86/entry/common.c:195 [inline]
 syscall_return_slowpath+0x490/0x550 arch/x86/entry/common.c:264
 entry_SYSCALL_64_fastpath+0x9e/0xa0
RIP: 0033:0x452f19
RSP: 002b:00007f0b9bda4ce8 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca
RAX: 0000000000000000 RBX: 000000000071bec8 RCX: 0000000000452f19
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 000000000071bec8
RBP: 000000000071bec8 R08: 0000000000000125 R09: 000000000071bea0
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000a2f7cf R14: 00007f0b9bda59c0 R15: 0000000000000000
Dumping ftrace buffer:
   (ftrace buffer empty)
Kernel Offset: disabled
Rebooting in 86400 seconds..