Re: [PATCH] daemon.c: avoid accessing ss_family member of struct sockaddr_storage

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On Mon, 15 Mar 2010, Jeff King wrote:

> On Mon, Mar 15, 2010 at 04:03:00PM -0500, Brandon Casey wrote:
> 
> > When NO_SOCKADDR_STORAGE is set for a platform, either sockaddr_in or
> > sockaddr_in6 is used intead.  Neither of which has an ss_family member.
> > They have an sin_family and sin6_family member respectively.  Since the
> > addrcmp() function accesses the ss_family member of a sockaddr_storage
> > struct, compilation fails on platforms which define NO_SOCKADDR_STORGAGE.
> > 
> > Since any sockaddr_* structure can be cast to a struct sockaddr and
> > have its sa_family member read, do so here to workaround this issue.
> 
> Didn't Gary say that AIX 5.2 sticks sa_len at the front of their
> sockaddr?

Yes, but if they have it in sockaddr, they have it in sockaddr_in (and 
should have it in sockaddr_storage, if it defines such fields at all). 
Those structs should always be defined so that their 
sa_family/ss_family/sin_family/sin6_family fields match.

> We know that whatever we actually have (an actual sockaddr_storage, or a
> sockaddr_in, or a sockaddr_in6) will have the family at the front, so
> can you just cast it to sa_family_t?
> 
> Or am I wrong in assuming that, and on AIX sockaddr_in actually has
> sa_len at the front, so casting to sockaddr does the right thing (and my
> recommendation above would actually be broken)? The AIX boxen I have
> access to are all down at the moment.

Generally, I don't think one can assume much about the layout of these 
structs, there may be this sa_len field on some implementations.

But you should always be able to cast a sockaddr_in or sockaddr_in6 or 
sockaddr_storage to a sockaddr, to examine its sa_family field, in order 
to know what to cast it to.

// Martin
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