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

From: Eric Biggers <[email-masked]>
Date: Tue, 8 May 2018 22:40:54 -0700

On Wed, May 09, 2018 at 07:23:41AM +0200, 'Dmitry Vyukov' via syzkaller-bugs wrote:
> On Wed, May 9, 2018 at 7:05 AM, Eric Biggers <[email-masked]> wrote:
> > On Sat, May 05, 2018 at 05:57:02PM -0700, syzbot wrote:
> >> Hello,
> >>
> >> syzbot found the following crash on:
> >>
> >> HEAD commit:    c1c07416cdd4 Merge tag 'kbuild-fixes-v4.17' of git://git.k..
> >> git tree:       upstream
> >> console output: https://syzkaller.appspot.com/x/log.txt?x=13d5de47800000
> >> kernel config:  https://syzkaller.appspot.com/x/.config?x=5a1dc06635c10d27
> >> dashboard link: https://syzkaller.appspot.com/bug?extid=99858724c0ba555a12ea
> >> compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
> >> syzkaller repro:https://syzkaller.appspot.com/x/repro.syz?x=170afde7800000
> >> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=141b4be7800000
> >>
> >> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> >> Reported-by: [email-masked]
> >>
> >> random: sshd: uninitialized urandom read (32 bytes read)
> >> random: sshd: uninitialized urandom read (32 bytes read)
> >> random: sshd: uninitialized urandom read (32 bytes read)
> >> random: sshd: uninitialized urandom read (32 bytes read)
> >> 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: 0 PID: 4495 Comm: syz-executor551 Not tainted 4.17.0-rc3+ #34
> >> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> >> Google 01/01/2011
> >> Call Trace:
> >>  <IRQ>
> >>  __dump_stack lib/dump_stack.c:77 [inline]
> >>  dump_stack+0x1b9/0x294 lib/dump_stack.c:113
> >>  tfrc_rx_hist_sample_rtt.cold.3+0x54/0x5c
> >> net/dccp/ccids/lib/packet_history.c:422
> >>  ccid3_hc_rx_packet_recv+0x5c8/0xed0 net/dccp/ccids/ccid3.c:765
> >>  ccid_hc_rx_packet_recv net/dccp/ccid.h:185 [inline]
> >>  dccp_deliver_input_to_ccids+0xf0/0x280 net/dccp/input.c:180
> >>  dccp_rcv_established+0x87/0xb0 net/dccp/input.c:378
> >>  dccp_v4_do_rcv+0x153/0x180 net/dccp/ipv4.c:654
> >>  sk_backlog_rcv include/net/sock.h:909 [inline]
> >>  __sk_receive_skb+0x3a2/0xd60 net/core/sock.c:513
> >>  dccp_v4_rcv+0x10e5/0x1f3f net/dccp/ipv4.c:875
> >>  ip_local_deliver_finish+0x2e3/0xd80 net/ipv4/ip_input.c:215
> >>  NF_HOOK include/linux/netfilter.h:288 [inline]
> >>  ip_local_deliver+0x1e1/0x720 net/ipv4/ip_input.c:256
> >>  dst_input include/net/dst.h:450 [inline]
> >>  ip_rcv_finish+0x81b/0x2200 net/ipv4/ip_input.c:396
> >>  NF_HOOK include/linux/netfilter.h:288 [inline]
> >>  ip_rcv+0xb70/0x143d net/ipv4/ip_input.c:492
> >>  __netif_receive_skb_core+0x26f5/0x3630 net/core/dev.c:4592
> >>  __netif_receive_skb+0x2c/0x1e0 net/core/dev.c:4657
> >>  process_backlog+0x219/0x760 net/core/dev.c:5337
> >>  napi_poll net/core/dev.c:5735 [inline]
> >>  net_rx_action+0x7b7/0x1930 net/core/dev.c:5801
> >>  __do_softirq+0x2e0/0xaf5 kernel/softirq.c:285
> >>  do_softirq_own_stack+0x2a/0x40 arch/x86/entry/entry_64.S:1046
> >>  </IRQ>
> >>  do_softirq.part.17+0x14d/0x190 kernel/softirq.c:329
> >>  do_softirq arch/x86/include/asm/preempt.h:23 [inline]
> >>  __local_bh_enable_ip+0x1ec/0x230 kernel/softirq.c:182
> >>  local_bh_enable include/linux/bottom_half.h:32 [inline]
> >>  rcu_read_unlock_bh include/linux/rcupdate.h:728 [inline]
> >>  ip_finish_output2+0xab2/0x1840 net/ipv4/ip_output.c:231
> >>  ip_finish_output+0x828/0xf80 net/ipv4/ip_output.c:317
> >>  NF_HOOK_COND include/linux/netfilter.h:277 [inline]
> >>  ip_output+0x21b/0x850 net/ipv4/ip_output.c:405
> >>  dst_output include/net/dst.h:444 [inline]
> >>  ip_local_out+0xc5/0x1b0 net/ipv4/ip_output.c:124
> >>  ip_queue_xmit+0x9d7/0x1f70 net/ipv4/ip_output.c:504
> >>  dccp_transmit_skb+0x999/0x12e0 net/dccp/output.c:142
> >>  dccp_xmit_packet+0x250/0x790 net/dccp/output.c:281
> >>  dccp_write_xmit+0x190/0x1f0 net/dccp/output.c:363
> >>  dccp_sendmsg+0x8c7/0x1020 net/dccp/proto.c:818
> >>  inet_sendmsg+0x19f/0x690 net/ipv4/af_inet.c:798
> >>  sock_sendmsg_nosec net/socket.c:629 [inline]
> >>  sock_sendmsg+0xd5/0x120 net/socket.c:639
> >>  ___sys_sendmsg+0x525/0x940 net/socket.c:2117
> >>  __sys_sendmmsg+0x240/0x6f0 net/socket.c:2212
> >>  __do_sys_sendmmsg net/socket.c:2241 [inline]
> >>  __se_sys_sendmmsg net/socket.c:2238 [inline]
> >>  __x64_sys_sendmmsg+0x9d/0x100 net/socket.c:2238
> >>  do_syscall_64+0x1b1/0x800 arch/x86/entry/common.c:287
> >>  entry_SYSCALL_64_after_hwframe+0x49/0xbe
> >> RIP: 0033:0x445d09
> >> RSP: 002b:00007f3c7eff5d88 EFLAGS: 00000293 ORIG_RAX: 0000000000000133
> >> RAX: ffffffffffffffda RBX: 00000000006dac40 RCX: 0000000000445d09
> >> RDX: 0000000000000001 RSI: 000000
> >>
> >>
> >> ---
> >> This bug is generated by a bot. It may contain errors.
> >> See https://goo.gl/tpsmEJ for more information about syzbot.
> >> syzbot engineers can be reached at [email-masked].
> >>
> >> syzbot will keep track of this bug report.
> >> If you forgot to add the Reported-by tag, once the fix for this bug is
> >> merged
> >> into any tree, please reply to this email with:
> >> #syz fix: exact-commit-title
> >> If you want to test a patch for this bug, please reply with:
> >> #syz test: git://repo/address.git branch
> >> and provide the patch inline or as an attachment.
> >> To mark this as a duplicate of another syzbot report, please reply with:
> >> #syz dup: exact-subject-of-another-report
> >
> > There's already a bug report with this title, this one just had a few characters
> > truncated from the end.  Dmitry, is that intentional?  The other one is
> > https://groups.google.com/forum/#!msg/syzkaller-bugs/u5nq3PdPkIc/bBFjKHXPAgAJ:
> >
> > #syz dup: BUG: please report to [email-masked] => prev = 0, last = 0 at net/dccp/ccids/lib/packet_history.c:LINE/tfrc_rx_hist_sample_rtt()
> 
> I think this happened when we started truncating kernel crash titles
> to 120 columns, so it's intentional.
> However, the dup command did not pass. It's hard to understand who
> received what today, but this suggests that somebody altered email in
> the command to [email-masked]:
> https://groups.google.com/forum/message/raw?msg=syzkaller-bugs/GMndq4-h7BI/VIz4aBEOAwAJ
> We can also mark the old one as invalid.
> 

Ah, that was my fault -- I must have copied the bug title from the
syzkaller-bugs Google Groups page, which had mangled the email address in the
bug title.  The actual title was:

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