refcount_t: underflow; use-after-free.
------------[ cut here ]------------
WARNING: CPU: 1 PID: 30905 at lib/refcount.c:186 refcount_sub_and_test+0x167/0x1b0 lib/refcount.c:186
Kernel panic - not syncing: panic_on_warn set ...

CPU: 1 PID: 30905 Comm: syz-executor2 Not tainted 4.13.0-rc4+ #3
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:180
 __warn+0x1c4/0x1d9 kernel/panic.c:541
 report_bug+0x211/0x2d0 lib/bug.c:183
 fixup_bug+0x40/0x90 arch/x86/kernel/traps.c:190
 do_trap_no_signal arch/x86/kernel/traps.c:224 [inline]
 do_trap+0x260/0x390 arch/x86/kernel/traps.c:273
 do_error_trap+0x120/0x390 arch/x86/kernel/traps.c:310
 do_invalid_op+0x1b/0x20 arch/x86/kernel/traps.c:323
 invalid_op+0x1e/0x30 arch/x86/entry/entry_64.S:846
RIP: 0010:refcount_sub_and_test+0x167/0x1b0 lib/refcount.c:186
RSP: 0018:ffff8801c5bc6928 EFLAGS: 00010282
RAX: 0000000000000026 RBX: 0000000000000001 RCX: 0000000000000000
RDX: 0000000000000026 RSI: 1ffff10039937ddc RDI: ffffed0038b78d19
RBP: ffff8801c5bc69b8 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 1ffff10038b78d26
R13: 00000000ffffff01 R14: 0000000000000100 R15: ffff8801d6190a3c
 sctp_wfree+0x183/0x620 net/sctp/socket.c:7747
 skb_release_head_state+0x124/0x200 net/core/skbuff.c:616
 skb_release_all+0x15/0x60 net/core/skbuff.c:629
 __kfree_skb net/core/skbuff.c:645 [inline]
 consume_skb+0x153/0x490 net/core/skbuff.c:705
 sctp_chunk_destroy net/sctp/sm_make_chunk.c:1437 [inline]
 sctp_chunk_put+0x29c/0x420 net/sctp/sm_make_chunk.c:1464
 sctp_chunk_free+0x53/0x60 net/sctp/sm_make_chunk.c:1451
 __sctp_outq_teardown+0xc7d/0x15a0 net/sctp/outqueue.c:264
 sctp_outq_free+0x15/0x20 net/sctp/outqueue.c:284
 sctp_association_free+0x2d0/0x930 net/sctp/associola.c:357
 sctp_cmd_delete_tcb net/sctp/sm_sideeffect.c:919 [inline]
 sctp_cmd_interpreter net/sctp/sm_sideeffect.c:1333 [inline]
 sctp_side_effects net/sctp/sm_sideeffect.c:1200 [inline]
 sctp_do_sm+0x28e7/0x6d90 net/sctp/sm_sideeffect.c:1171
 sctp_primitive_SHUTDOWN+0xa0/0xd0 net/sctp/primitive.c:104
 sctp_close+0x3c6/0x980 net/sctp/socket.c:1532
 inet_release+0xed/0x1c0 net/ipv4/af_inet.c:425
 inet6_release+0x50/0x70 net/ipv6/af_inet6.c:432
 sock_release+0x8d/0x1e0 net/socket.c:597
 sock_close+0x16/0x20 net/socket.c:1126
 __fput+0x327/0x7e0 fs/file_table.c:210
 ____fput+0x15/0x20 fs/file_table.c:246
 task_work_run+0x18a/0x260 kernel/task_work.c:116
 exit_task_work include/linux/task_work.h:21 [inline]
 do_exit+0xa3a/0x1b10 kernel/exit.c:865
 do_group_exit+0x149/0x400 kernel/exit.c:969
 SYSC_exit_group kernel/exit.c:980 [inline]
 SyS_exit_group+0x1d/0x20 kernel/exit.c:978
 entry_SYSCALL_64_fastpath+0x1f/0xbe
RIP: 0033:0x4512e9
RSP: 002b:0000000000a6f9e8 EFLAGS: 00000206 ORIG_RAX: 00000000000000e7
RAX: ffffffffffffffda RBX: 0000000001dac914 RCX: 00000000004512e9
RDX: 00000000004512e9 RSI: 0000000000765328 RDI: 0000000000000000
RBP: 0000000000000086 R08: 00000000007180a8 R09: 0000000000001615
R10: 0000000000765320 R11: 0000000000000206 R12: 0000000000000015
R13: 0000000000000014 R14: 000000000000012b R15: 000000000000001d
Dumping ftrace buffer:
   (ftrace buffer empty)
Kernel Offset: disabled
Rebooting in 86400 seconds..