Bug#435646: AI_ADDRCONFIG
This is an informational mail that I hope helps some people since
this problem had been bothering me for a long time and I just
solved it for myself. Bug#435646 shows up high (#1) in certain
Google search results and I believe the submitter of merged
Bug#470289 had the same issue as me.
Since glibc v2.3.3, getaddrinfo() has included a feature to
disable AAAA requests if there are no interfaces with IPv6
addresses; the feature is turned on by a flag called
AI_ADDRCONFIG.
The patch in Bug#435646 that was installed and then reverted was
about changing the behavior of AI_ADDRCONFIG so that it only
includes *globally-scoped* addresses in this check. (Some people
do talk to localhost via IPv6 so this patch doesn't work.)
When IPv6 is disabled in the kernel via "alias net-pf-10 off",
there are no IPv6 addresses *period*, so the original unpatched
getaddrinfo() should already work.
Having not fully understood the issue before, I lamented the
rejection of the patch, thinking this was about disabling AAAA
even if there are no IPv6 addresses period --- because various
apps *do* make AAAA requests with IPv6 completely disabled in the
kernel! But as it turns out, the regular feature has already
existed since glibc 2.3.3.
Here's the answer: users of getaddrinfo() aren't using the
feature! It's only enabled by default if hints=NULL, otherwise
you have to enable it explicitly with hints->flags =
AI_ADDRCONFIG. Each application that uses getaddrinfo() needs to
pass in the AI_ADDRCONFIG flag, and programmers may not know about
it.
I think getaddrinfo() should read from gai.conf to allow this to
enabled system-wide. Until then, I've written a kludge that can
be installed in LD_PRELOAD or /etc/ld.so.preload to force on this
flag (and an alternate kludge to just always turn off AAAA
queries).
http://git.cubewano.org/git/gai-no6
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