xkb: Use snprintf to measure string lengths instead of manual strlen math

nx-X11/programs/Xserver/xkb/ddxLoad.c

@@ -404,15 +404,16 @@ FILE *	file;
                 &&(!isalpha(xkm_output_dir[0]) || xkm_output_dir[1]!=':')
 #endif
                 ) {
-	    if (strlen(XkbBaseDirectory)+strlen(xkm_output_dir)
-		     +strlen(mapName)+6 <= PATH_MAX)
-	    {
-	        sprintf(buf,"%s/%s%s.xkm",XkbBaseDirectory,
-					xkm_output_dir,mapName);
-	    }
+	     if (snprintf(buf, PATH_MAX, "%s/%s%s.xkm", XkbBaseDirectory,
+                           xkm_output_dir, mapName) >= PATH_MAX)
+	          buf[0] = '\0';
+	}
+	else
+	{
+	      if (snprintf(buf, PATH_MAX, "%s%s.xkm", xkm_output_dir, mapName)
+		  >= PATH_MAX)
+                  buf[0] = '\0';
 	}
-	else if (strlen(xkm_output_dir)+strlen(mapName)+5 <= PATH_MAX)
-	    sprintf(buf,"%s%s.xkm",xkm_output_dir,mapName);
 	if (buf[0] != '\0')
 	    file= fopen(buf,"rb");
 	else file= NULL;
@@ -505,9 +506,9 @@ XkbRF_RulesPtr	rules;
 	sprintf(buf,"rules/%s",rules_name);
     }
     else {
-	if (strlen(XkbBaseDirectory)+strlen(rules_name)+8 > PATH_MAX)
+	if (snprintf(buf, PATH_MAX, "%s/rules/%s", XkbBaseDirectory, rules_name)
+	    >= PATH_MAX)
 	    return False;
-        sprintf(buf,"%s/rules/%s",XkbBaseDirectory,rules_name);
     }
     if ((file= fopen(buf,"r"))==NULL)
 	return False;

nx-X11/programs/Xserver/xkb/maprules.c

@@ -953,9 +953,8 @@ Bool		ok;
     if ((!base)||(!rules))
 	return False;
     if (locale) {
-	if (strlen(base)+strlen(locale)+2 > PATH_MAX)
+        if (snprintf(buf, PATH_MAX, "%s-%s", base, locale) >= PATH_MAX)
 	    return False;
-	sprintf(buf,"%s-%s", base, locale);
     }
     else {
 	if (strlen(base)+1 > PATH_MAX)