Subject: BUG: please report to [email-masked] => prev = 0, last = 0 at net/dccp/ccids/lib/packet_history.c:LINE/tfrc_rx_hist_sample_rtt()

From: syzbot <[email-masked]>
Date: Thu, 18 Jan 2018 01:34:02 -0800

syzbot has found reproducer for the following crash on linux-next commit
a362f6d2cdbd089dd7040ba66dcb0ad276a20cf7 (Thu Jan 18 07:07:54 2018 +0000)
Add linux-next specific files for 20180118

So far this crash happened 185 times on linux-next, mmots, net-next,  
upstream.
C reproducer is attached.
syzkaller reproducer is attached.
Raw console output is attached.
compiler: gcc (GCC) 7.1.1 20170620
.config is attached.

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by:  
[email-masked]
It will help syzbot understand when the bug is fixed.

BUG: please report to [email-masked] => prev = 0, last = 0 at  
net/dccp/ccids/lib/packet_history.c:425/tfrc_rx_hist_sample_rtt()
CPU: 1 PID: 6246 Comm: syzkaller158939 Not tainted  
4.15.0-rc8-next-20180118+ #100
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
Call Trace:
  <IRQ>
  __dump_stack lib/dump_stack.c:17 [inline]
  dump_stack+0x194/0x257 lib/dump_stack.c:53
  tfrc_rx_hist_sample_rtt+0x407/0x4d0 net/dccp/ccids/lib/packet_history.c:422
  ccid3_hc_rx_packet_recv+0x696/0xeb3 net/dccp/ccids/ccid3.c:765
  ccid_hc_rx_packet_recv net/dccp/ccid.h:185 [inline]
  dccp_deliver_input_to_ccids+0xd9/0x250 net/dccp/input.c:180
  dccp_rcv_established+0x88/0xb0 net/dccp/input.c:378
  dccp_v4_do_rcv+0x135/0x160 net/dccp/ipv4.c:653
  sk_backlog_rcv include/net/sock.h:908 [inline]
  __sk_receive_skb+0x33e/0xc10 net/core/sock.c:513
  dccp_v4_rcv+0xf5f/0x1c80 net/dccp/ipv4.c:874
  ip_local_deliver_finish+0x2f1/0xc50 net/ipv4/ip_input.c:216
  NF_HOOK include/linux/netfilter.h:288 [inline]
  ip_local_deliver+0x1ce/0x6e0 net/ipv4/ip_input.c:257
  dst_input include/net/dst.h:449 [inline]
  ip_rcv_finish+0x953/0x1e30 net/ipv4/ip_input.c:397
  NF_HOOK include/linux/netfilter.h:288 [inline]
  ip_rcv+0xc5a/0x1840 net/ipv4/ip_input.c:493
  __netif_receive_skb_core+0x1a41/0x3460 net/core/dev.c:4537
  __netif_receive_skb+0x2c/0x1b0 net/core/dev.c:4602
  process_backlog+0x203/0x740 net/core/dev.c:5282
  napi_poll net/core/dev.c:5680 [inline]
  net_rx_action+0x792/0x1910 net/core/dev.c:5746
  __do_softirq+0x2d7/0xb85 kernel/softirq.c:285
  do_softirq_own_stack+0x2a/0x40 arch/x86/entry/entry_64.S:1150
  </IRQ>
  do_softirq.part.19+0x14d/0x190 kernel/softirq.c:329
  do_softirq kernel/softirq.c:177 [inline]
  __local_bh_enable_ip+0x1ee/0x230 kernel/softirq.c:182
  local_bh_enable include/linux/bottom_half.h:32 [inline]
  rcu_read_unlock_bh include/linux/rcupdate.h:726 [inline]
  ip_finish_output2+0x962/0x1550 net/ipv4/ip_output.c:231
  ip_finish_output+0x864/0xd10 net/ipv4/ip_output.c:317
  NF_HOOK_COND include/linux/netfilter.h:277 [inline]
  ip_output+0x1d2/0x860 net/ipv4/ip_output.c:405
  dst_output include/net/dst.h:443 [inline]
  ip_local_out+0x95/0x160 net/ipv4/ip_output.c:124
  ip_queue_xmit+0x8c0/0x18e0 net/ipv4/ip_output.c:504
  dccp_transmit_skb+0x9ac/0x10f0 net/dccp/output.c:142
  dccp_xmit_packet+0x215/0x740 net/dccp/output.c:281
  dccp_write_xmit+0x17d/0x1d0 net/dccp/output.c:363
  dccp_sendmsg+0x95f/0xdc0 net/dccp/proto.c:813
  inet_sendmsg+0x11f/0x5e0 net/ipv4/af_inet.c:764
  sock_sendmsg_nosec net/socket.c:630 [inline]
  sock_sendmsg+0xca/0x110 net/socket.c:640
  ___sys_sendmsg+0x767/0x8b0 net/socket.c:2020
  __sys_sendmsg+0xe5/0x210 net/socket.c:2054
  SYSC_sendmsg net/socket.c:2065 [inline]
  SyS_sendmsg+0x2d/0x50 net/socket.c:2061
  entry_SYSCALL_64_fastpath+0x29/0xa0
RIP: 0033:0x446469
RSP: 002b:00007fcecb23bda8 EFLAGS: 00000293 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00000000006dbc3c RCX: 0000000000446469
RDX: 0000000000000080 RSI: 00000000206c8000 RDI: 0000000000000005
RBP: 00000000006dbc38 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000293 R12: f8e4cbe49e572d45
R13: 54c1b85d98aba1df R14: a6eaa24dbeb18c29 R15: 000000000000000c