Re: T_DNAME handling in getaddrinfo() and gethostname()

[Ignatios Souvatzis <is%netbsd.org@localhost>]

Hi,

a correction of the obfuscated example:

On Fri, Nov 13, 2020 at 09:04:14PM +0100, Ignatios Souvatzis wrote:
> 
> I connect to machines below foo.example.de, which is a convenience domain
> otherwise identical to the german-language and much slower to type 
> fumfiefoebarbaz.example.de, and foo happens to be the two letter acronym 
> for the english translation of fumfiefoebarbaz.
> 
> In the new world order, the admins have replaced the include file
> mess with a DNAME record, redirecting

foo.example.de to fumfiefoebarbaz.example.de

> This works fine, but the programs on my netbsd machines connecting there
> spam the console log with syslog messages about getting DNAME answers
> when they expected AAAA and A (which are send as additional info by the
> recursive resolver daemon).
> 
> I investigated in the sources, and found that getaddrinfo() and
> gethnamaddr() - the latter being the core of the implementation
> for gethostbyname() and gethostbyaddr() - special-case T_CNAME,
> T_SIG and T_KEY answers in the result returned, but not T_DNAME.
> 
> While a full handling of T_DNAME seems to complicated - we'd need to
> splice in the new domain instead of the old in the query - it also
> isn't necessary, as the resolver daemon already does all the work - see
> 
> 
> ;; QUESTION SECTION:
> ;qq.foo.example.de.           IN      A
> 
> ;; ANSWER SECTION:
> foo.example.de.                1772 IN  DNAME   fumfiefoebarbaz.example.de.
> qq.foo.example.de.             1772 IN  CNAME   qq.fumfiefoebarbaz.example.de.
> qq.fumfiefoebarbaz.example.de. 3200 IN  A       192.0.2.63
> 
> 
> So all that remains to do is to suppress the syslog call also in this 
> case. Patch below; I'll commit unless technical serious objections are
> raised (Tested on -9.0_ish machine, compiles on -current, no code
> differences).
> 
> Regards
> 	-is
> 
> 
> Index: include/arpa/nameser_compat.h
> ===================================================================
> RCS file: /cvsroot/src/include/arpa/nameser_compat.h,v
> retrieving revision 1.7
> diff -u -r1.7 nameser_compat.h
> --- include/arpa/nameser_compat.h	28 Jun 2020 02:16:19 -0000	1.7
> +++ include/arpa/nameser_compat.h	13 Nov 2020 19:17:44 -0000
> @@ -210,6 +210,7 @@
>  #define T_ATMA		ns_t_atma
>  #define T_NAPTR		ns_t_naptr
>  #define T_A6		ns_t_a6
> +#define T_DNAME		ns_t_dname
>  #define	T_TSIG		ns_t_tsig
>  #define	T_IXFR		ns_t_ixfr
>  #define T_AXFR		ns_t_axfr
> Index: lib/libc/net/getaddrinfo.c
> ===================================================================
> RCS file: /cvsroot/src/lib/libc/net/getaddrinfo.c,v
> retrieving revision 1.119
> diff -u -r1.119 getaddrinfo.c
> --- lib/libc/net/getaddrinfo.c	13 Dec 2018 04:41:41 -0000	1.119
> +++ lib/libc/net/getaddrinfo.c	13 Nov 2020 19:17:45 -0000
> @@ -1821,7 +1821,7 @@
>  				continue;
>  			}
>  		} else if (type != qtype) {
> -			if (type != T_KEY && type != T_SIG) {
> +			if (type != T_KEY && type != T_SIG && type != T_DNAME) {
>  				struct syslog_data sd = SYSLOG_DATA_INIT;
>  				syslog_r(LOG_NOTICE|LOG_AUTH, &sd,
>  	       "gethostby*.getanswer: asked for \"%s %s %s\", got type \"%s\"",
> Index: lib/libc/net/gethnamaddr.c
> ===================================================================
> RCS file: /cvsroot/src/lib/libc/net/gethnamaddr.c,v
> retrieving revision 1.92
> diff -u -r1.92 gethnamaddr.c
> --- lib/libc/net/gethnamaddr.c	22 Sep 2015 16:16:02 -0000	1.92
> +++ lib/libc/net/gethnamaddr.c	13 Nov 2020 19:17:45 -0000
> @@ -358,7 +358,7 @@
>  			continue;
>  		}
>  		if (type != qtype) {
> -			if (type != T_KEY && type != T_SIG)
> +			if (type != T_KEY && type != T_SIG && type != T_DNAME)
>  				syslog(LOG_NOTICE|LOG_AUTH,
>  	       "gethostby*.getanswer: asked for \"%s %s %s\", got type \"%s\"",
>  				       qname, p_class(C_IN), p_type(qtype),