Re: Merging ns_parse from Alpine

[Rich Felker <dalias@libc.org>]

On Sun, Dec 14, 2014 at 08:05:36PM +0100, Felix Janda wrote:
> Rich Felker wrote:
> > On Sun, Dec 14, 2014 at 08:38:15AM +0100, Felix Janda wrote:
> > > Rich Felker wrote:
> > > > I'm working on merging Timo's patch for ns_parse:
> > > > 
> > > > http://git.alpinelinux.org/cgit/aports/tree/main/musl/1001-add-basic-dns-record-parsing-functions.patch?id=81d50064c335467fdfd80368bac6707d70db1af7
> > > > 
> > > > The first issue that came up in the process is that arpa/nameser.h,
> > > > which was previously not used by musl itself and really should never
> > > > have been accepted in its current form, is full of junk like
> > > > statement-expressions. Including it in a file that will be compiled
> > > > with musl adds build dependency on these nonstandard features. I
> > > > cleaned that up with no problem (just un-inlining the macros since
> > > > we're adding function versions anyway), but there are a few more
> > > > issues.
> > > 
> > > The NS_GET* macros still seem to be used a lot in the code.
> > 
> > Yes because they also advance the pointer, and this behavior was
> > intentional in the code. I don't think it hurts to use them once
> > they're fixed to be function calls.
> 
> I likely just missunderstood you. With un-inlining the macros you mean
> making them call the ns_get* functions? (That seems reasonable.)

Right:

#define NS_GET16(s, cp) (void)((s) = ns_get16(((cp)+=2)-2))
#define NS_GET32(l, cp) (void)((l) = ns_get32(((cp)+=4)-4))
#define NS_PUT16(s, cp) ns_put16((s), ((cp)+=2)-2)
#define NS_PUT32(l, cp) ns_put32((l), ((cp)+=4)-4)

> > > > 	r = dn_expand(handle->_msg, handle->_eom, handle->_msg_ptr, rr->name, NS_MAXDNAME);
> > > > 	if (r < 0) return -1;
> > > 
> > > dn_expand doesn't set errno.
> > 
> > Maybe we should just call ns_name_uncompress (below) instead here?
> > 
> > > [...]
> > > > int ns_name_uncompress(const unsigned char *msg, const unsigned char *eom,
> > > >                        const unsigned char *src, char *dst, size_t dstsiz)
> > > > {
> > > > 	int r;
> > > > 	r = dn_expand(msg, eom, src, dst, dstsiz);
> > > > 	if (r < 0) errno = EMSGSIZE;
> > > > 	return r;
> > > > }
> > 
> > Does that sound better?
> 
> That should work. I have no particular opinion on whether to call
> ns_name_uncompress or to jump to "size".

Indeed, ns_name_uncompress doesn't set any errors except EMSGSIZE. The
only ways dn_expand can fail are truncated buffers or malformed
messages that would attempt to read outside the buffer, and I think
EMSGSIZE is reasonable for either of these.

Rich