Avoid reverse resolution for server name

A NFS client should be able to work properly even if the DNS Reverse record
for the server is not set. There is no excuse to forcefully prevent that
from working when it can.

This patch adds a new pair of options (-z/-Z) that allow to turn on/off
DNS reverse resolution for determining the server name to use with GSSAPI.

To avoid breaking current behavior the option defaults to off by default,
ideally we will turn this on by default after a transition period.

Signed-off-by: Simo Sorce <simo@redhat.com>

3 files changed, 31 insertions, 6 deletions

diff --git a/utils/gssd/gss_util.h b/utils/gssd/gss_util.h
index aa9f778..663fb09 100644
--- a/utils/gssd/gss_util.h
+++ b/utils/gssd/gss_util.h
@@ -52,4 +52,6 @@ int gssd_check_mechs(void);
 		gss_krb5_set_allowable_enctypes(min, cred, num, types)
 #endif
 
+extern int avoid_ptr;
+
 #endif /* _GSS_UTIL_H_ */
diff --git a/utils/gssd/gssd.c b/utils/gssd/gssd.c
index 07b1e52..1f0ac0c 100644
--- a/utils/gssd/gssd.c
+++ b/utils/gssd/gssd.c
@@ -85,7 +85,7 @@ sig_hup(int signal)
 static void
 usage(char *progname)
 {
-	fprintf(stderr, "usage: %s [-f] [-l] [-M] [-n] [-v] [-r] [-p pipefsdir] [-k keytab] [-d ccachedir] [-t timeout] [-R preferred realm]\n",
+	fprintf(stderr, "usage: %s [-f] [-l] [-M] [-n] [-v] [-r] [-p pipefsdir] [-k keytab] [-d ccachedir] [-t timeout] [-R preferred realm] [-z] [-Z]\n",
 		progname);
 	exit(1);
 }
@@ -102,7 +102,7 @@ main(int argc, char *argv[])
 	char *progname;
 
 	memset(ccachesearch, 0, sizeof(ccachesearch));
-	while ((opt = getopt(argc, argv, "fvrlmnMp:k:d:t:R:")) != -1) {
+	while ((opt = getopt(argc, argv, "fvrlmnMp:k:d:t:R:zZ")) != -1) {
 		switch (opt) {
 			case 'f':
 				fg = 1;
@@ -150,6 +150,12 @@ main(int argc, char *argv[])
 				errx(1, "Encryption type limits not supported by Kerberos libraries.");
 #endif
 				break;
+			case 'z':
+				avoid_ptr = 1;
+				break;
+			case 'Z':
+				avoid_ptr = 0;
+				break;
 			default:
 				usage(argv[0]);
 				break;
diff --git a/utils/gssd/gssd_proc.c b/utils/gssd/gssd_proc.c
index d6f07e6..b123978 100644
--- a/utils/gssd/gssd_proc.c
+++ b/utils/gssd/gssd_proc.c
@@ -67,6 +67,7 @@
 #include <errno.h>
 #include <gssapi/gssapi.h>
 #include <netdb.h>
+#include <ctype.h>
 
 #include "gssd.h"
 #include "err_util.h"
@@ -107,6 +108,8 @@ struct pollfd * pollarray;
 
 unsigned long pollsize;  /* the size of pollaray (in pollfd's) */
 
+int avoid_ptr = 0;
+
 /*
  * convert a presentation address string to a sockaddr_storage struct. Returns
  * true on success or false on failure.
@@ -165,12 +168,26 @@ addrstr_to_sockaddr(struct sockaddr *sa, const char *node, const char *port)
  * convert a sockaddr to a hostname
  */
 static char *
-sockaddr_to_hostname(const struct sockaddr *sa, const char *addr)
+get_servername(const char *name, const struct sockaddr *sa, const char *addr)
 {
 	socklen_t		addrlen;
 	int			err;
 	char			*hostname;
 	char			hbuf[NI_MAXHOST];
+	unsigned char		buf[sizeof(struct in6_addr)];
+	int			do_ptr_lookup = 0;
+
+	if (avoid_ptr) {
+		/* try to determine if this is a name, or an IP address.
+		 * If it is an IP fallback to a PTR lookup */
+		if (strchr(name, '.') && inet_pton(AF_INET, name, buf) == 1)
+			do_ptr_lookup = 1; /* IPv4 */
+		else if (strchr(name, ':') && inet_pton(AF_INET6, name, buf) == 1)
+			do_ptr_lookup = 1; /* or IPv6 */
+		if (!do_ptr_lookup) {
+			return strdup(name);
+		}
+	}
 
 	switch (sa->sa_family) {
 	case AF_INET:
@@ -208,7 +225,7 @@ read_service_info(char *info_file_name, char **servicename, char **servername,
 		  struct sockaddr *addr) {
 #define INFOBUFLEN 256
 	char		buf[INFOBUFLEN + 1];
-	static char	dummy[128];
+	static char	server[128];
 	int		nbytes;
 	static char	service[128];
 	static char	address[128];
@@ -236,7 +253,7 @@ read_service_info(char *info_file_name, char **servicename, char **servername,
 		   "service: %127s %15s version %15s\n"
 		   "address: %127s\n"
 		   "protocol: %15s\n",
-		   dummy,
+		   server,
 		   service, program, version,
 		   address,
 		   protoname);
@@ -258,7 +275,7 @@ read_service_info(char *info_file_name, char **servicename, char **servername,
 	if (!addrstr_to_sockaddr(addr, address, port))
 		goto fail;
 
-	*servername = sockaddr_to_hostname(addr, address);
+	*servername = get_servername(server, addr, address);
 	if (*servername == NULL)
 		goto fail;