Subject: unaligned data object from SIOCGIFCONF
To: None <firstname.lastname@example.org>
From: Jun-ichiro itojun Hagino <email@example.com>
Date: 02/20/2000 01:35:24
With introduction of IPv6, SIOCGIFCONF can return unaligned data
object for 64bit arch (like alpha). Situation is like this:
- SIOCGIFCONF returns packed structs
- sizeof(sockaddr_in6) % 8 != 0
- so, data object from SIOCGIFCONF can be placed at "addr % 8 != 0".
If this raises too many problem for old binaries (those which does not
copy data object from SIOCGIFCONF, and try to access the content
directly with pointer), I can think of several solutions:
- change SIOCGIFCONF to new number
- old number should remain as OSIOCGIFCONF, which returns
non-large sockaddr (= not IPv6)
- add 4-byte padding after sockaddr_in6
this may violate RFC2553 3.3
(solution 3 - not really a solution)
- it was bug in the userland tools that tries to use pointers to
access packed struct. they should have copied them.
actually the alignment assumption breaks with sockaddr_dl,
and several other sockaddr variants. so IPv6 is not the wrong guy.
I was notified from <firstname.lastname@example.org> of the problem in ypbind
and other places, and put fixes there - but I'm now wondering if how
many of them needs fixes.
I think solution 3 is the right way ("broken userland programs should
be bitten"), but if it bites too many userland programs, we may better
pick solution 1. Thoughts? comments?