segment fault at dns.c

[Justin]

Hi, there.

I was using mtr 0.83 on archlinux and met segment fault. The following is what i got through gdb.

Program received signal SIGSEGV, Segmentation fault. Packets Pings
0x000000000040928a in dorequest (s=0x8978c0 <tempstring> "1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.ip6.arpa", type=12,
    id=11508) at dns.c:941
941 if (NSSOCKADDR6(i)->sin6_family == AF_INET6)
(gdb) where
#0 0x000000000040928a in dorequest (s=0x8978c0 <tempstring> "1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.ip6.arpa", type=
    12, id=11508) at dns.c:941
#1 0x000000000040947b in resendrequest (rp=0x9346a8, type=12) at dns.c:976
#2 0x0000000000409572 in sendrequest (rp=0x9346a8, type=12) at dns.c:993
#3 0x000000000040ab9b in dns_lookup2 (ip=0x6114e0 <host>) at dns.c:1459
#4 0x000000000040abd0 in dns_lookup (ip=0x6114e0 <host>) at dns.c:1469
#5 0x00000000004031b1 in mtr_curses_hosts (startstat=99) at curses.c:355
#6 0x000000000040406c in mtr_curses_redraw () at curses.c:614
#7 0x000000000040b1b8 in display_redraw () at display.c:141
#8 0x000000000040c51b in select_loop () at select.c:103
#9 0x000000000040b2f7 in display_loop () at display.c:217
#10 0x0000000000404cd0 in main (argc=1, argv=0x7fffffffe9b8) at mtr.c:475

so if i use option --no-dns, everything would work fine.

I have ipv6 enabled and connected.

cheers,

[Justin (justin-w-xd)]

And another strange thing is that i also installed same version of mtr in my laptop, which also have the same updated archlinux, but everything works fine there.

[Jonne Haß (mrzyx)]

I can confirm this bug in the same environment (Arch, v6). The --no-dns option or removing the v6 nameserver entry from /etc/resolv.conf "fixes" this bug.

[Yannis Aribaud (bugs-d6bell)]

I confirm this bug too. I also try to compile the last mtr version 0.84 which suffer the same issue...

[Antonio Querubin (aaq)]

What is in your /etc/resolv.conf?

[Justin (justin-w-xd)]

it was
```
nameserver 2001:470:20::2
```
in my resolv.conf, and after i change it to
```
nameserver 8.8.8.8
```
segment fault was gone.

[Gerry (gerrydm)]

I can confirm this bug, also using mtr 0.83-1 on Arch.
If it helps: this bug does not exist in the mtr version that is currently in Debian Wheezy (0.82-3).

[mutantmonkey (mutantmonkey)]

I have done some testing on Arch with 0.84-1. It appears this bug is triggered when you have mixed IPv6 and IPv4 nameservers in /etc/resolv.conf. If you have only one address family, the bug does not occur.

[mutantmonkey (mutantmonkey)]

I opened a pull request on Github with a patch that fixes this issue: https://github.com/traviscross/mtr/pull/5