syzbot

refcount_t: underflow; use-after-free.
------------[ cut here ]------------
WARNING: CPU: 1 PID: 20526 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: 1 PID: 20526 Comm: syz-executor3 Not tainted 4.14.0-rc4+ #85
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:ffff8801a3d07220 EFLAGS: 00010212
RAX: 0000000000010000 RBX: ffff8801c5935800 RCX: ffffc90002ef4000
RDX: 000000000000093f RSI: ffffffff8417f5c9 RDI: ffff8801c5935a60
RBP: ffff8801a3d07348 R08: 0000000000000000 R09: 1ffff100347a0e95
R10: ffff8801d7a1c340 R11: 00000000b877b192 R12: 1ffff100347a0e54
R13: 0000000000000000 R14: ffffffff847daa20 R15: ffff8801c5935950
 sctp_destruct_sock+0x43/0x50 net/sctp/socket.c:4508
 __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:1652 [inline]
 sctp_close+0x487/0x980 net/sctp/socket.c:1560
 inet_release+0xed/0x1c0 net/ipv4/af_inet.c:426
 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:244
 task_work_run+0x199/0x270 kernel/task_work.c:112
 get_signal+0x1343/0x16d0 kernel/signal.c:2164
 do_signal+0x94/0x1ee0 arch/x86/kernel/signal.c:808
 exit_to_usermode_loop+0x214/0x310 arch/x86/entry/common.c:158
 prepare_exit_to_usermode arch/x86/entry/common.c:197 [inline]
 syscall_return_slowpath+0x42f/0x510 arch/x86/entry/common.c:266
 entry_SYSCALL_64_fastpath+0xbc/0xbe
RIP: 0033:0x452719
RSP: 002b:00007fcb6e910be8 EFLAGS: 00000212 ORIG_RAX: 000000000000002b
RAX: fffffffffffffff2 RBX: 00000000007580d8 RCX: 0000000000452719
RDX: 0000000020b51ffc RSI: 0000000020b52000 RDI: 0000000000000013
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000212 R12: 00000000006ee0a0
R13: 00000000ffffffff R14: 00007fcb6e9116d4 R15: 000000000000000a
Dumping ftrace buffer:
   (ftrace buffer empty)
Kernel Offset: disabled
Rebooting in 86400 seconds..