[RFC PATCH 1/3] libnfsidmap: Query DNS for the the NFSv4 domain

[Steve Dickson <steved@redhat.com>]

In domain_from_dns(), when at the hostname is a FQHN
query the DNS server for the _nfsv4idmapdomain TXT
record. If the record exists, use that as the
NFSv4 domain.

Note, this query will only happen if the domain name
is not set in the /etc/idmapd.conf

Signed-off-by: Steve Dickson <steved@redhat.com>
---
 libnfsidmap.c | 104 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 103 insertions(+), 1 deletion(-)

diff --git a/libnfsidmap.c b/libnfsidmap.c
index 2db4d13..7b8c0ed 100644
--- a/libnfsidmap.c
+++ b/libnfsidmap.c
@@ -53,6 +53,10 @@
 #include <stdarg.h>
 #include <dlfcn.h>
 #include <ctype.h>
+#include <resolv.h>
+#include <arpa/nameser.h>
+#include <arpa/nameser_compat.h>
+
 #include "nfsidmap.h"
 #include "nfsidmap_internal.h"
 #include "cfg.h"
@@ -79,6 +83,11 @@ gid_t nobody_gid = (gid_t)-1;
 #define IDMAPD_DEFAULT_DOMAIN "localdomain"
 #endif
 
+#ifndef NFS4DNSTXTREC
+#define NFS4DNSTXTREC "_nfsv4idmapdomain"
+#endif
+
+
 /* Default logging fuction */
 static void default_logger(const char *fmt, ...)
 {
@@ -114,6 +123,93 @@ static int id_as_chars(char *name, uid_t *id)
 	return 1;
 }
 
+static int dns_txt_query(char *domain, char **nfs4domain)
+{
+	char *txtname = NFS4DNSTXTREC;
+	char *msg, *answ, *eom, *mptr; 
+	int len, status = -1;
+	HEADER *hdr;
+	
+	msg = calloc(1, NS_MAXMSG);
+	if (msg == NULL)
+		return -1;
+
+	answ = calloc(1, NS_MAXMSG);
+	if (answ == NULL) {
+		free(msg);
+		return -1;
+	}
+
+	if (res_init() < 0) {
+		IDMAP_LOG(2, ("libnfsidmap: res_init() failed for %s.%s: %s\n",
+			txtname, domain, hstrerror(h_errno)));
+		goto freemem;
+	}
+	len = res_querydomain(txtname, domain, C_IN, T_TXT, msg, NS_MAXMSG);
+	if (len < 0) {
+		IDMAP_LOG(2, ("libnfsidmap: res_querydomain() failed for %s.%s: %s\n",
+			txtname, domain, hstrerror(h_errno)));
+		goto freemem;
+	}
+	hdr = (HEADER *)msg;
+
+	/* See if there is an answer */
+	if (ntohs(hdr->ancount) < 1) {
+		IDMAP_LOG(2, ("libnfsidmap: No TXT record for %s.%s\n",
+			txtname, domain));
+		goto freemem;
+	}
+	/* find the EndOfMessage */
+	eom = msg + len;
+
+	/* skip header */
+	mptr = &msg[HFIXEDSZ];
+
+	/* skip name field in question section */
+	mptr += dn_skipname(mptr, eom) + QFIXEDSZ;
+
+	/* read in the question */
+	len = dn_expand(msg, eom, mptr, answ, NS_MAXDNAME);
+	if (len < 0) { /* does this really matter?? */
+		IDMAP_LOG(2, ("libnfsidmap: No question section for %s.%s: %s\n",
+			txtname, domain, hstrerror(h_errno)));
+		goto freemem;
+	}
+
+	/*
+	 * Now, dissect the answer section, Note: if there
+	 * are more than one answer only the first
+	 * one will be used. 
+	 */
+
+	/* skip passed the name field  */
+	mptr += dn_skipname(mptr, eom);
+	/* skip pass the type class and ttl fields */
+	mptr += 2 + 2 + 4;
+
+	/* make sure there is some data */
+	GETSHORT(len, mptr);
+	if (len < 0) {
+		IDMAP_LOG(2, ("libnfsidmap: No data in answer for %s.%s\n",
+			txtname, domain));
+		goto freemem;
+	}
+	/* get the lenght field */
+	len = (int)*mptr++;
+	/* copy the data */
+	memcpy(answ, mptr, len);
+	answ[len] = '\0';
+	
+	*nfs4domain = strdup(answ);
+	status = 0;
+
+freemem:
+	free(msg);
+	free(answ);
+
+	return (status);
+}
+
 static int domain_from_dns(char **domain)
 {
 	struct hostent *he;
@@ -125,7 +221,13 @@ static int domain_from_dns(char **domain)
 		return -1;
 	if ((c = strchr(he->h_name, '.')) == NULL || *++c == '\0')
 		return -1;
-	*domain = strdup(c);
+	/* 
+	 * Query DNS to see if the _nfsv4idmapdomain TXT record exists
+	 * If so use it... 
+	 */
+	if (dns_txt_query(c, domain) < 0)
+		*domain = strdup(c);
+
 	return 0;
 }
 
-- 
2.7.4