Avoid accessing NULL when ipv6 is disabled but ipv6 args or options are used

[ghost]

This fix is intended to prevent a segmentation fault.
Here is how I understood it:

In TargetGroup.cc:661 :
result << inet_ntop_ez((struct sockaddr_storage *) &this->addr, sizeof(this->addr)) << "/" << bits;
Here, inet_ntop_ez returns NULL because IPV6 is disabled by default. The calling function (or parent) NetBlockIPv6Netmask::str() return result.str() which produces a segmentation fault.

With this fix, inet_ntop_ez do not check if IPv6 is disabled, so it will return the address even if it's disabled, then the check will be made by the parent calling function TargetGroup::get_next_host (targets.cc:392). Before, this->netblock->str().c_str() was causing the crash, now the error handles it normally, telling you to add -6 option if you didn't, and if you do nmap.cc will yell at you at line 1045 because you don't have IPv6 enabled.

Waiting for feedback,
Cheers

[dmiller-nmap]

Related #328

[dmiller-nmap]

@W0naN0w I don't see how this is really related, but it may be a needed change anyway. Can you detail here the configure options and Nmap command you used to trigger the crash? Thanks.

[ghost]

Hello @dmiller-nmap, I configured Nmap this way: ./configure --disable-ipv6 as you suggested. I then used ./nmap 2a00:1450:400b:c03:0:0:0:63 after make, which was producing a segmentation fault, but now warns that we need the -6 option. So if I enter ./nmap -6 2a00:1450:400b:c03:0:0:0:63 now, Nmap will yell that my libpcap does not have IPv6 enabled:

I am afraid IPv6 is not available because your host doesn't support it or you chose to compile Nmap w/o IPv6 support.
QUITTING!

What options could I use to produce the crash you want to fix, please?

[ghost]

That's it, we now have a reasonable fix. I just don't understand why the travis build failed... Waiting for feedback!