added DNS spoofing test to host access control

socket.c

@@ -327,8 +327,10 @@ char *client_name(int fd)
 	int     length = sizeof(sa);
 	static char name_buf[100];
 	struct hostent *hp;
+	char **p;
+	char *def = "UNKNOWN";
 
-	strcpy(name_buf,"UNKNOWN");
+	strcpy(name_buf,def);
 
 	if (getpeername(fd, &sa, &length)) {
 		exit_cleanup(1);
@@ -341,5 +343,23 @@ char *client_name(int fd)
 		strlcpy(name_buf,(char *)hp->h_name,sizeof(name_buf) - 1);
 	}
 
+
+	/* do a forward lookup as well to prevent spoofing */
+	hp = gethostbyname(name_buf);
+	if (!hp) {
+		strcpy(name_buf,def);
+		rprintf(FERROR,"reverse name lookup failed\n");
+	} else {
+		for (p=hp->h_addr_list;*p;p++) {
+			if (memcmp(*p, &sockin->sin_addr, hp->h_length) == 0) {
+				break;
+			}
+		}
+		if (!*p) {
+			strcpy(name_buf,def);
+			rprintf(FERROR,"reverse name lookup mismatch - spoofed address?\n");
+		} 
+	}
+
 	return name_buf;
 }