[Kea-users] Remote debugging in KEA

[Hreiðar Jóelsson]

thanks, I was not able to get gdb working remotely with Clion but I managed to get some trace of the crash by running it locally on the server. The problem is that I’m not sure what to make of it 😊

Thread 1 "kea-dhcp4" received signal SIGSEGV, Segmentation fault.
0x00007ffe4c2338b8 in ?? ()
(gdb) bt
#0  0x00007ffe4c2338b8 in ?? ()
#1  0x00007f5f823fb960 in isc::dhcp::LibDHCP::packOptions4 (buf=..., options=std::multimap with 8 elements = {...}) at libdhcp++.cc:805
#2  0x00007f5f8244acda in isc::dhcp::Pkt4::pack (this=0x557a5c8d2060) at pkt4.cc:138
#3  0x0000557a5b6258f9 in isc::dhcp::Dhcpv4Srv::processPacketPktSend (this=this at entry=0x7ffe4c234960, callout_handle=..., query=..., rsp=...) at dhcp4_srv.cc:1163
#4  0x0000557a5b62ebf9 in isc::dhcp::Dhcpv4Srv::processPacket (this=this at entry=0x7ffe4c234960, query=..., rsp=..., allow_packet_park=allow_packet_park at entry=true) at dhcp4_srv.cc:1110
#5  0x0000557a5b62fd25 in isc::dhcp::Dhcpv4Srv::run_one (this=this at entry=0x7ffe4c234960) at dhcp4_srv.cc:821
#6  0x0000557a5b6302f8 in isc::dhcp::Dhcpv4Srv::run (this=0x7ffe4c234960) at dhcp4_srv.cc:723
#7  0x0000557a5b603466 in main (argc=<optimized out>, argv=<optimized out>) at main.cc:227

I ‘we discovered that the server crashes when I feed in DHCP option using isc::asiolink::IOAddress, where the type is ipv4-address, like option 6 – domain-name-servers. Maybe someone can show an example of how one should go about overwriting those kinds of options.

Here is more info if someone got some ideas. This is the code that adds the new option to the response object and some log lines just before KEA dies:

# add IPAddress option - called from pkt4_send hook
void add4OptionIPAddress(Pkt4Ptr& response, uint8_t opt_code, std::string& opt_value)
    {
        OptionPtr opt = response->getOption(opt_code);
        if(opt)
        {
           response -> delOption(opt_code);
        }
        Option4AddrLst newIpList(opt_code);
        if(opt_value.find(",") != std::string::npos)
        {
                isc::asiolink::IOAddress addr1(opt_value.substr(0,opt_value.find(",")));
                newIpList.addAddress(addr1);

                isc::asiolink::IOAddress addr2(opt_value.substr(opt_value.find(",")+1));
                newIpList.addAddress(addr2);
        }
        else
        {
              isc::asiolink::IOAddress addr3(opt_value);
              newIpList.addAddress(addr3);
        }
        opt.reset( &newIpList );
        LOG_DEBUG(my_logger, 50, "dns server list %1").arg(opt->toText());
        LOG_DEBUG(my_logger, 50, "responce befor leave %1 ").arg(response->toText());
        response->addOption(opt);
        LOG_DEBUG(my_logger, 50, "responce after leave %1 ").arg(response->toText());
    }

# my_logger last line
2018-11-02 14:43:06.377 DEBUG [kea-dhcp4.my_logger/29189] responce befor leave local_address=83.173.15.80:67, remote_address=10.206.0.2:67, msg_type=DHCPACK (5), transid=0x76fc973b,
options:
  type=001, len=004: 4294967040 (uint32)
  type=003, len=004: 83.173.30.1
  type=006, len=008: 1.1.1.1 8.8.8.8
  type=015, len=013: "gagnaveita.is" (string)
  type=051, len=004: 60 (uint32)
  type=053, len=001: 5 (uint8)
  type=054, len=004: 83.173.15.80
  type=061, len=007: 01:50:a7:2b:ea:cc:e3

# kea-dhcp4 last lines
2018-11-02 14:43:06.377 DEBUG [kea-dhcp4.callouts/29189] HOOKS_CALLOUTS_COMPLETE completed callouts for hook pkt4_send (total callouts duration: 0.402 ms)
2018-11-02 14:43:06.377 DEBUG [kea-dhcp4.options/29189] DHCP4_PACKET_PACK [hwtype=1 50:a7:2b:ea:cc:e3], cid=[01:50:a7:2b:ea:cc:e3], tid=0x76fc973b: preparing on-wire format of the packet to be sent


regards, Hreiðar.

From: EZELINK TELECOM <lex at ezelink.com>
Sent: Friday, November 2, 2018 12:46 PM
To: Hreiðar Jóelsson <hreidar.joelsson at gagnaveita.is>
Cc: kea-users at lists.isc.org
Subject: Re: [Kea-users] Remote debugging in KEA

gdb attach should be enough.
Or if you are running keadhcp from start - then just gdb .../keadhcp.. <options>
You can also force system to create core files after crashes
On Fri, Nov 2, 2018, 15:20 Hreiðar Jóelsson <hreidar.joelsson at gagnaveita.is<mailto:hreidar.joelsson at gagnaveita.is> wrote:
Hi, can anyone help me or point me in the right direction regarding remote debugging and KEA. I’m developing a hook that queries external Redis database for lease policies and uses them to choose subnet and manipulate DHCP options for incoming requests. My problem is that Kea is crashing in the main process after a pass it a new DHCP option 6 so I need to be able to debug what is going on there. I’m trying to setup remote debug using gdbserver and Jetbrains Clion an I have manage to start a debugging session on my KEA server and connect to it from my development machine but KEA does not run. Any ideas on how this works?

Best Regards,
Hreiðar Jóelsson
Network Engineer
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