segfault in bird v1.6.4

[Alexander Velkov]

Hello bird-team,
I have a bird v1.6.4. configuration that works fine.
A certain set of actions leads to a segfault and a crash of the bird binary.

I have configured and built bird 1.6.4. with IPv6 support that runs on a
box with a i686 linux with kernel v4.14.75. My bird configuration:

### bird6.conf:

protocol device {
  scan time 10;
}

protocol direct C_main {
  interface "*";
  preference 255;
  check link;
}

protocol kernel K_main {
  preference 255;
  scan time 20;
  export all;
  learn;
}

include "*.conff";

### ospfv3.conff in the same directory:

debug protocols all;
log syslog { info, remote, warning, error, auth, fatal, bug };

protocol ospf O_main {
  preference 145;
  instance id 0;

  area 172.16.0.0 {

    interface "vti0" {
      dead 120;
      hello 30;
      cost 1;
      priority 1;
      type pointopoint;

      neighbors {
        fe80::e68:3ff:fe26:5130;
      };
    };

    interface "eth1" {
      dead 40;
      hello 10;
      cost 1;
      priority 1;
      type broadcast;
      stub yes;
    };
  };

  import filter {
    accept;
  };
  export filter {
    reject;
  };
}

### The following actions lead to a crash of bird6:

EEPD[~]# /sbin/bird6 -P /var/run/bird6.pid -c /var/etc/bird6/bird6.conf

Oct 24 14:23:08 EEPD info  bird6   [ 4684]: Started

EEPD[~]# ps | grep bird6
 4930 root      1500 S    /sbin/bird6 -P /var/run/bird6.pid -c
/var/etc/bird6/bird6.conf
 4932 root      1284 S    grep bird6

EEPD[~]#
EEPD[~]# ip -6 link add vti0 type vti6 local fd00::38 remote fd00::1b ikey
2 okey 2;
EEPD[~]# ip -6 link set vti0 up;
EEPD[~]# ifconfig vti0 mtu 1422

Oct 24 14:23:17 EEPD err   bird6   [ 4684]: KIF: Received address message
for unknown interface 33
Oct 24 14:23:20 EEPD err   bird6   [ 4684]: O_main: Socket error on vti0:
Invalid argument
Oct 24 14:23:20 EEPD info  kernel: [ 4684]: segfault at 58e ip b7eed103 sp
bf9acad8 error 4 in libuClibc-1.0.30.so[b7ebd000+72000]

EEPD[~]#
EEPD[~]# ps | grep bird6
 4988 root      1284 S    grep bird6
EEPD[~]#

### Further testing
- bird does NOT crash if the contents of bird6.conf and ospfv3.conf are
placed in a single file without inclusion.
- bird does NOT crash if the call 'ifconfig vti0 mtu 1422' is executed
before 'ip -6 link set vti0 up'.

Hope this information helps.

Best Regards
Alex
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