[Bug network/19791] res_query.c:262 asserts when dns contains unreachable entries

["ppadmavilasom at vmware dot com" <sourceware-bugzilla at sourceware dot org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=19791

--- Comment #2 from priyesh <ppadmavilasom at vmware dot com> ---
(In reply to Florian Weimer from comment #1)
> (In reply to priyesh from comment #0)
> 
> > res_query.c:262: __libc_res_nquery: Assertion `(hp != ((void *)0)) && (hp2
> > != ((void *)0))' failed.
> 
> What's the exact glibc version you tested?  Current master would print a
> different assertion due to commit 8ba14398e629c1f63b9c91a59a47a713b3cce8bc.

2.23 with no patches

> 
> > This can be triggered by disabling ipv6, then adding an ipv6 dns and using
> > the proof of concept here:
> > https://github.com/fjserna/CVE-2015-7547/blob/master/CVE-2015-7547-client.c
> 
> How did you disable IPv6?  There multiple ways to do this (at least
> partially).
add the following to /etc/sysctl.conf and do sysctl -p
net.ipv6.conf.all.disable_ipv6 = 1
net.ipv6.conf.default.disable_ipv6 = 1
net.ipv6.conf.lo.disable_ipv6 = 1

make sure that dns has an ipv6 entry. in my test, ipv6 was the first entry

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