- (djm) OpenBSD CVS Sync

   - markus@cvs.openbsd.org 2003/06/02 09:17:34
     [auth2-hostbased.c auth.c auth-options.c auth-rhosts.c auth-rh-rsa.c]
     [canohost.c monitor.c servconf.c servconf.h session.c sshd_config]
     [sshd_config.5]
     deprecate VerifyReverseMapping since it's dangerous if combined
     with IP based access control as noted by Mike Harding; replace with
     a UseDNS option, UseDNS is on by default and includes the
     VerifyReverseMapping check; with itojun@, provos@, jakob@ and deraadt@
     ok deraadt@, djm@
 - (djm) Fix portable-specific uses of verify_reverse_mapping too

1 files changed, 27 insertions, 17 deletions

diff --git a/canohost.c b/canohost.c
index 417d95c1..533f2c24 100644
--- a/canohost.c
+++ b/canohost.c
@@ -12,7 +12,7 @@
  */
 
 #include "includes.h"
-RCSID("$OpenBSD: canohost.c,v 1.36 2003/04/08 20:21:28 itojun Exp $");
+RCSID("$OpenBSD: canohost.c,v 1.37 2003/06/02 09:17:34 markus Exp $");
 
 #include "packet.h"
 #include "xmalloc.h"
@@ -27,7 +27,7 @@ static void check_ip_options(int, char *);
  */
 
 static char *
-get_remote_hostname(int socket, int verify_reverse_mapping)
+get_remote_hostname(int socket, int use_dns)
 {
 	struct sockaddr_storage from;
 	int i;
@@ -72,6 +72,9 @@ get_remote_hostname(int socket, int verify_reverse_mapping)
 	    NULL, 0, NI_NUMERICHOST) != 0)
 		fatal("get_remote_hostname: getnameinfo NI_NUMERICHOST failed");
 
+	if (!use_dns)
+		return xstrdup(ntop);
+
 	if (from.ss_family == AF_INET)
 		check_ip_options(socket, ntop);
 
@@ -80,14 +83,24 @@ get_remote_hostname(int socket, int verify_reverse_mapping)
 	if (getnameinfo((struct sockaddr *)&from, fromlen, name, sizeof(name),
 	    NULL, 0, NI_NAMEREQD) != 0) {
 		/* Host name not found.  Use ip address. */
-#if 0
-		logit("Could not reverse map address %.100s.", ntop);
-#endif
 		return xstrdup(ntop);
 	}
 
-	/* Got host name. */
-	name[sizeof(name) - 1] = '\0';
+	/*
+	 * if reverse lookup result looks like a numeric hostname,
+	 * someone is trying to trick us by PTR record like following:
+	 *	1.1.1.10.in-addr.arpa.	IN PTR	2.3.4.5
+	 */
+	memset(&hints, 0, sizeof(hints));
+	hints.ai_socktype = SOCK_DGRAM;	/*dummy*/
+	hints.ai_flags = AI_NUMERICHOST;
+	if (getaddrinfo(name, "0", &hints, &ai) == 0) {
+		logit("Nasty PTR record \"%s\" is set up for %s, ignoring",
+		    name, ntop);
+		freeaddrinfo(ai);
+		return xstrdup(ntop);
+	}
+
 	/*
 	 * Convert it to all lowercase (which is expected by the rest
 	 * of this software).
@@ -95,9 +108,6 @@ get_remote_hostname(int socket, int verify_reverse_mapping)
 	for (i = 0; name[i]; i++)
 		if (isupper(name[i]))
 			name[i] = tolower(name[i]);
-
-	if (!verify_reverse_mapping)
-		return xstrdup(name);
 	/*
 	 * Map it back to an IP address and check that the given
 	 * address actually is an address of this host.  This is
@@ -180,14 +190,14 @@ check_ip_options(int socket, char *ipaddr)
  */
 
 const char *
-get_canonical_hostname(int verify_reverse_mapping)
+get_canonical_hostname(int use_dns)
 {
 	static char *canonical_host_name = NULL;
-	static int verify_reverse_mapping_done = 0;
+	static int use_dns_done = 0;
 
 	/* Check if we have previously retrieved name with same option. */
 	if (canonical_host_name != NULL) {
-		if (verify_reverse_mapping_done != verify_reverse_mapping)
+		if (use_dns_done != use_dns)
 			xfree(canonical_host_name);
 		else
 			return canonical_host_name;
@@ -196,11 +206,11 @@ get_canonical_hostname(int verify_reverse_mapping)
 	/* Get the real hostname if socket; otherwise return UNKNOWN. */
 	if (packet_connection_is_on_socket())
 		canonical_host_name = get_remote_hostname(
-		    packet_get_connection_in(), verify_reverse_mapping);
+		    packet_get_connection_in(), use_dns);
 	else
 		canonical_host_name = xstrdup("UNKNOWN");
 
-	verify_reverse_mapping_done = verify_reverse_mapping;
+	use_dns_done = use_dns;
 	return canonical_host_name;
 }
 
@@ -294,11 +304,11 @@ get_remote_ipaddr(void)
 }
 
 const char *
-get_remote_name_or_ip(u_int utmp_len, int verify_reverse_mapping)
+get_remote_name_or_ip(u_int utmp_len, int use_dns)
 {
 	static const char *remote = "";
 	if (utmp_len > 0)
-		remote = get_canonical_hostname(verify_reverse_mapping);
+		remote = get_canonical_hostname(use_dns);
 	if (utmp_len == 0 || strlen(remote) > utmp_len)
 		remote = get_remote_ipaddr();
 	return remote;