Re: [PATCH] Skip logging for additional DNSSEC records from RFC4034 [BZ 14841]

["Carlos O'Donell" <carlos at redhat dot com>]

On 02/19/2015 12:00 PM, Siddhesh Poyarekar wrote:
> RFC 4034 specifies 3 more record types (RRSIG, NSEC, DNSKEY) that the
> glibc resolver does not identify.  The resolver would log a message in
> syslog if debugging is enabled in resolv.conf and RES_USE_DNSSEC is
> set in the _res struct.  This was fine before since we did not set the
> DO bit, but we do so now, so skip logging the message when we have
> requested DNSSEC.

Exactly, there is no reason to log anything if we are asking for DNSSEC
support.

> I have not added the identifiers to res_debug.c on purpose - it serves
> no value other than adding an ABI event for libresolv since we're just
> ignoring these records.

Agreed (somewhat, see below).

> Tested on x86_64.
> 
> 	[BZ #14841]
> 	* resolv/arpa/nameser.h (__ns_type): Add ns_t_rrsig, ns_t_nsec
> 	and ns_t_dnskey.
> 	* resolv/arpa/nameser_compat.h (T_RRSIG, T_NSEC, T_DNSKEY):
> 	Define.
> 	* resolv/gethnamaddr.c (getanswer): Use them to ignore DNSSEC
> 	records.  Skip logging if RES_USE_DNSSEC is set.
> 	* resolv/nss_dns/dns-host.c (getanswer_r): Likewise.

Almost there.

One request:

Add comments to res_debug.c to indicate that these identifiers
need to be added when required. This way a reviewer does not
see them missing and wonders why they weren't added.

> ---
>  resolv/arpa/nameser.h        |  3 +++
>  resolv/arpa/nameser_compat.h |  3 +++
>  resolv/gethnamaddr.c         | 21 +++++++++++++--------
>  resolv/nss_dns/dns-host.c    | 19 +++++++++++++------
>  4 files changed, 32 insertions(+), 14 deletions(-)
> 
> diff --git a/resolv/arpa/nameser.h b/resolv/arpa/nameser.h
> index fb8513b..372d5cd 100644
> --- a/resolv/arpa/nameser.h
> +++ b/resolv/arpa/nameser.h
> @@ -293,6 +293,9 @@ typedef enum __ns_type {
>  	ns_t_sink = 40,		/*%< Kitchen sink (experimentatl) */
>  	ns_t_opt = 41,		/*%< EDNS0 option (meta-RR) */
>  	ns_t_apl = 42,		/*%< Address prefix list (RFC3123) */
> +	ns_t_rrsig = 46,	/*%< DNSSEC RRset Signature (RFC4034) */
> +	ns_t_nsec = 47,		/*%< DNSSEC Next-Secure Record (RFC4034)*/
> +	ns_t_dnskey = 48,	/*%< DNSSEC key record (RFC4034) */

OK.

>  	ns_t_tkey = 249,	/*%< Transaction key */
>  	ns_t_tsig = 250,	/*%< Transaction signature. */
>  	ns_t_ixfr = 251,	/*%< Incremental zone transfer. */
> diff --git a/resolv/arpa/nameser_compat.h b/resolv/arpa/nameser_compat.h
> index d59c9e4..284bff7 100644
> --- a/resolv/arpa/nameser_compat.h
> +++ b/resolv/arpa/nameser_compat.h
> @@ -164,6 +164,9 @@ typedef struct {
>  #define T_NAPTR		ns_t_naptr
>  #define T_A6		ns_t_a6
>  #define T_DNAME		ns_t_dname
> +#define T_RRSIG		ns_t_rrsig
> +#define T_NSEC		ns_t_nsec
> +#define T_DNSKEY	ns_t_dnskey

OK.

>  #define	T_TSIG		ns_t_tsig
>  #define	T_IXFR		ns_t_ixfr
>  #define T_AXFR		ns_t_axfr
> diff --git a/resolv/gethnamaddr.c b/resolv/gethnamaddr.c
> index a861a84..9e0c498 100644
> --- a/resolv/gethnamaddr.c
> +++ b/resolv/gethnamaddr.c
> @@ -331,15 +331,20 @@ getanswer (const querybuf *answer, int anslen, const char *qname, int qtype)
>  			buflen -= n;
>  			continue;
>  		}
> -		if ((type == T_SIG) || (type == T_KEY) || (type == T_NXT)) {
> -			/* We don't support DNSSEC yet.  For now, ignore
> -			 * the record and send a low priority message
> -			 * to syslog.
> -			 */
> -			syslog(LOG_DEBUG|LOG_AUTH,
> +		if ((type == T_SIG) || (type == T_KEY) || (type == T_NXT)
> +		    || (type == T_RRSIG) || (type == T_NSEC)
> +		    || (type == T_DNSKEY)) {
> +		        /* We don't support DNSSEC responses yet, but we do
> +			 * allow setting the DO bit.  If the DNS server sent us
> +			 * these records without us asking for it, ignore the
> +			 * record and send a low priority message to syslog.
> +		         */
> +			if ((_res.options & RES_USE_DNSSEC) == 0) {
> +				syslog(LOG_DEBUG|LOG_AUTH,
>  	       "gethostby*.getanswer: asked for \"%s %s %s\", got type \"%s\"",
> -			       qname, p_class(C_IN), p_type(qtype),
> -			       p_type(type));
> +					qname, p_class(C_IN), p_type(qtype),
> +					p_type(type));
> +			}

OK.

>  			cp += n;
>  			continue;
>  		}
> diff --git a/resolv/nss_dns/dns-host.c b/resolv/nss_dns/dns-host.c
> index f715ab0..b10c94e 100644
> --- a/resolv/nss_dns/dns-host.c
> +++ b/resolv/nss_dns/dns-host.c
> @@ -822,13 +822,20 @@ getanswer_r (const querybuf *answer, int anslen, const char *qname, int qtype,
>  	}
>        if (__builtin_expect (type == T_SIG, 0)
>  	  || __builtin_expect (type == T_KEY, 0)
> -	  || __builtin_expect (type == T_NXT, 0))
> +	  || __builtin_expect (type == T_NXT, 0)
> +	  || __builtin_expect (type == T_RRSIG, 0)
> +	  || __builtin_expect (type == T_NSEC, 0)
> +	  || __builtin_expect (type == T_DNSKEY, 0))

OK.

>  	{
> -	  /* We don't support DNSSEC yet.  For now, ignore the record
> -	     and send a low priority message to syslog.  */
> -	  syslog (LOG_DEBUG | LOG_AUTH,
> -	       "gethostby*.getanswer: asked for \"%s %s %s\", got type \"%s\"",
> -		  qname, p_class (C_IN), p_type(qtype), p_type (type));
> +	  /* We don't support DNSSEC responses yet, but we do allow setting the
> +	     DO bit.  If the DNS server sent us these records without us asking
> +	     for it, ignore the record and send a low priority message to
> +	     syslog.  */
> +	  if ((_res.options & RES_USE_DNSSEC) == 0)
> +	    syslog (LOG_DEBUG | LOG_AUTH,
> +		    "gethostby*.getanswer: asked for \"%s %s %s\", "
> +		    "got type \"%s\"",
> +		    qname, p_class (C_IN), p_type(qtype), p_type (type));

OK.

>  	  cp += n;
>  	  continue;
>  	}
> 

Cheers,
Carlos.