Bug#442157: marked as done (getaddrinfo() does not prefer IPv6 address over IPv4 one)
Your message dated Thu, 13 Sep 2007 17:58:43 +0200
with message-id <46E95E33.9040109@aurel32.net>
and subject line Bug#442157: getaddrinfo() does not prefer IPv6 address over IPv4 one
has caused the attached Bug report to be marked as done.
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--- Begin Message ---
Package: libc6
Version: 2.3.6.ds1-13
Severity: important
getaddrinfo() does not prefer IPv6 addresses, even though it should
according to RFC 3484. I have debugged the issue and it all boils down
to match_prefix() in sysdeps/posix/getaddrinfo.c. The prefix test runs
like this:
while (bits > 8)
{
if (*mask != *val)
break;
++mask;
++val;
bits -= 8;
}
if (bits < 8)
{
if ((*mask & (0xff00 >> bits)) == (*val & (0xff00 >> bits)))
/* Match! */
break;
}
Of course, for prefix lengths which are a multiple of 8 the loop ends
prematurely and the subsequent test returns 8, so there is never a match
for these lengths. Since the prefix for IPv4 addresses is 96 bits long
(see default_precedence), IPv4 addresses get the default priority (40)
and not the correct one (10). I was able to fix this by changing the
condition to:
while (bits >= 8)
Since match_prefix() is used for labels as well, this bug probably also
breaks RFC 3484 rule 5 (Prefer matching label).
-- System Information:
Debian Release: 4.0
APT prefers stable
APT policy: (500, 'stable')
Architecture: i386 (i686)
Shell: /bin/sh linked to /bin/bash
Kernel: Linux 2.6.20.3
Locale: LANG=cs_CZ.UTF-8, LC_CTYPE=cs_CZ.UTF-8 (charmap=UTF-8)
Versions of packages libc6 depends on:
ii tzdata 2007b-1 Time Zone and Daylight Saving Time
libc6 recommends no packages.
-- no debconf information
--- End Message ---
--- Begin Message ---
Version: 2.4-1
Petr Tesarik a écrit :
> Package: libc6
> Version: 2.3.6.ds1-13
> Severity: important
>
> getaddrinfo() does not prefer IPv6 addresses, even though it should
> according to RFC 3484. I have debugged the issue and it all boils down
> to match_prefix() in sysdeps/posix/getaddrinfo.c. The prefix test runs
> like this:
>
> while (bits > 8)
> {
> if (*mask != *val)
> break;
>
> ++mask;
> ++val;
> bits -= 8;
> }
>
> if (bits < 8)
> {
> if ((*mask & (0xff00 >> bits)) == (*val & (0xff00 >> bits)))
> /* Match! */
> break;
> }
>
> Of course, for prefix lengths which are a multiple of 8 the loop ends
> prematurely and the subsequent test returns 8, so there is never a match
> for these lengths. Since the prefix for IPv4 addresses is 96 bits long
> (see default_precedence), IPv4 addresses get the default priority (40)
> and not the correct one (10). I was able to fix this by changing the
> condition to:
>
> while (bits >= 8)
>
> Since match_prefix() is used for labels as well, this bug probably also
> breaks RFC 3484 rule 5 (Prefer matching label).
>
This is fixed since glibc version 2.4-1.
--
.''`. Aurelien Jarno | GPG: 1024D/F1BCDB73
: :' : Debian developer | Electrical Engineer
`. `' aurel32@debian.org | aurelien@aurel32.net
`- people.debian.org/~aurel32 | www.aurel32.net
--- End Message ---
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