bisecting fixing commit since f56f3d0e65adb447b8b583c8ed4fbbe544c9bfde
building syzkaller on 598ca6c8b8766304c3b2865e38f5f301c39bd299
testing commit f56f3d0e65adb447b8b583c8ed4fbbe544c9bfde with gcc (GCC) 8.1.0
kernel signature: e926645ab199d0cf4b2c7e33859705cd8dc86b2c
all runs: crashed: WARNING: refcount bug in sock_wfree
testing current HEAD e1f7d50ae3a3ec342e87a9b1ce6787bfb8b3c08b
testing commit e1f7d50ae3a3ec342e87a9b1ce6787bfb8b3c08b with gcc (GCC) 8.1.0
kernel signature: 5ccbf45e02d582c392d174df3df64bd8016e751f
all runs: crashed: WARNING: refcount bug in sock_wfree
revisions tested: 2, total time: 23m7.364668173s (build: 16m0.284732183s, test: 6m23.05471079s)
the crash still happens on HEAD
commit msg: Linux 4.14.160
crash: WARNING: refcount bug in sock_wfree
IPv6: ADDRCONF(NETDEV_UP): veth1_to_hsr: link is not ready
IPv6: ADDRCONF(NETDEV_UP): bridge0: link is not ready
IPv6: ADDRCONF(NETDEV_CHANGE): veth1_to_hsr: link becomes ready
refcount_t: underflow; use-after-free.
------------[ cut here ]------------
WARNING: CPU: 1 PID: 6960 at lib/refcount.c:187 refcount_sub_and_test.cold.13+0x13/0x1c lib/refcount.c:187
Kernel panic - not syncing: panic_on_warn set ...

CPU: 1 PID: 6960 Comm: syz-executor.4 Not tainted 4.14.160-syzkaller #0
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+0xf7/0x13b lib/dump_stack.c:58
 panic+0x1b0/0x358 kernel/panic.c:183
 __warn.cold.8+0x25/0x2c kernel/panic.c:547
 report_bug+0x1a4/0x1f3 lib/bug.c:186
 fixup_bug arch/x86/kernel/traps.c:177 [inline]
 do_error_trap+0x1bd/0x310 arch/x86/kernel/traps.c:295
 do_invalid_op+0x1b/0x20 arch/x86/kernel/traps.c:314
 invalid_op+0x1b/0x40 arch/x86/entry/entry_64.S:963
RIP: 0010:refcount_sub_and_test.cold.13+0x13/0x1c lib/refcount.c:187
RSP: 0018:ffff88807a387730 EFLAGS: 00010286
RAX: 0000000000000026 RBX: 0000000000008100 RCX: 0000000000000000
RDX: 0000000000000026 RSI: ffffffff86bcd8e0 RDI: ffffed100f470edd
RBP: ffff88807a387740 R08: ffff8880a5304ac8 R09: 0000000000000000
R10: 0000000000000000 R11: dffffc0000000000 R12: 0000000000008100
R13: ffff8880a82032bc R14: ffffffff883524e0 R15: 0000000000000000
 sock_wfree+0x9b/0x120 net/core/sock.c:1812
 sctp_wfree+0x28b/0x5f0 net/sctp/socket.c:7829
 skb_release_head_state+0xfc/0x1f0 net/core/skbuff.c:616
 skb_release_all+0xd/0x50 net/core/skbuff.c:629
 __kfree_skb net/core/skbuff.c:645 [inline]
 consume_skb+0x84/0x2a0 net/core/skbuff.c:705
 sctp_chunk_destroy net/sctp/sm_make_chunk.c:1442 [inline]
 sctp_chunk_put+0x150/0x230 net/sctp/sm_make_chunk.c:1469
 sctp_chunk_free+0x3f/0x50 net/sctp/sm_make_chunk.c:1456
 __sctp_outq_teardown+0x1a2/0xe10 net/sctp/outqueue.c:228
 sctp_outq_free+0x9/0x10 net/sctp/outqueue.c:284
 sctp_association_free+0x1d5/0x711 net/sctp/associola.c:358
 sctp_cmd_delete_tcb net/sctp/sm_sideeffect.c:924 [inline]
 sctp_cmd_interpreter net/sctp/sm_sideeffect.c:1312 [inline]
 sctp_side_effects net/sctp/sm_sideeffect.c:1179 [inline]
 sctp_do_sm+0x2141/0x4910 net/sctp/sm_sideeffect.c:1150
 sctp_primitive_ABORT+0x7c/0xc0 net/sctp/primitive.c:119
 sctp_close+0x23e/0x710 net/sctp/socket.c:1560
 inet_release+0xd9/0x1c0 net/ipv4/af_inet.c:425
 __sock_release+0xc2/0x2a0 net/socket.c:602
 sock_close+0x10/0x20 net/socket.c:1139
 __fput+0x232/0x750 fs/file_table.c:210
 ____fput+0x9/0x10 fs/file_table.c:244
 task_work_run+0xe5/0x170 kernel/task_work.c:113
 tracehook_notify_resume include/linux/tracehook.h:191 [inline]
 exit_to_usermode_loop+0x16a/0x1b0 arch/x86/entry/common.c:164
 prepare_exit_to_usermode arch/x86/entry/common.c:199 [inline]
 syscall_return_slowpath arch/x86/entry/common.c:270 [inline]
 do_syscall_64+0x416/0x5b0 arch/x86/entry/common.c:297
 entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x4141d1
RSP: 002b:00007ffeba090d50 EFLAGS: 00000293 ORIG_RAX: 0000000000000003
RAX: 0000000000000000 RBX: 0000000000000007 RCX: 00000000004141d1
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000006
RBP: 0000000000000001 R08: ffffffffffffffff R09: ffffffffffffffff
R10: 00007ffeba090e30 R11: 0000000000000293 R12: 000000000075bf20
R13: 000000000000ce07 R14: 0000000000761400 R15: 000000000075bf2c
Kernel Offset: disabled
Rebooting in 86400 seconds..