[lfs-dev] #3172: Glibc bug

Bruce Dubbs bruce.dubbs at gmail.com
Mon Aug 27 18:11:49 PDT 2012


Armin K. wrote:

> Hey, thank you for adding the patch. I was unable to reproduce it with
> anything. It just happened twice with glibc 2.16.0 ... I used 2.14.1 for
> some months and it never happened there. I still don't know what causes
> it, but it's fine to have a fix!

 From what I read, it is a problem with name servers.  DNS usually works 
with udp, but if the record is large, it can be tcp.  If for some reason 
a DNS message is broken up into multiple packets, there might be a 
problem with that.  On top of that, the name server software may be 
doing the wrong thing under certain circumstances or it may be 
misconfigured.

Usually DNS packets are quite small, for instance if you want ipv4 for 
www.xyz.com, that can be compressed into 4 bytes, but the DNS server 
also sends the nameserver and other information.  If there are a lot of 
addresses associated with a name, the messages get a bit larger.

The most likely thing that happened is that the sever sends 2 udp 
packets in response to a query and they arrive out of order.  The 
receiving code has to put them in the right order and in this case, I 
think it is the res_query code.  Under rare circumstances, it wasn't 
doing it correctly.

> As for -rc2, well I guess it might be good! I am out of bugs now :P
>
> Sorry for blocking the release.

You didn't block it.  I was planning for Saturday, but that can slip too 
if we think it necessary.

   -- Bruce






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