Do not allow non-ASCII symbols in filenames

ASCII symbols are still allowed.

qrexec-lib/gentbl.py

@@ -19,7 +19,7 @@ def print_interval(interval, last_cat):
         else:
             # Allow the interval consisting only of 0x20, to allow spaces in
             # file names
-            if last_cat[0] in ('C', 'Z') and interval != [0x20, 0x20]:
+            if (last_cat[0] in ('S', 'C', 'Z')) and interval[1] > 0x7E:
                 print_interval(interval, last_cat)
             interval = [i, i]
     print_interval(interval, last_cat)

qrexec-lib/unpack.c

@@ -253,6 +253,10 @@ static int validate_utf8_char(const unsigned char *untrusted_c) {
     if (!(U_IS_UNICODE_CHAR(code_point)))
         return 0;
 
+    /*
+     * Validate that the codepoint is a valid scalar value and is not a symbol,
+     * space, unassigned character, or control character.
+     */
     switch (code_point) {
 #include "unpack-table.c"
         return 0; // Invalid UTF-8 or forbidden codepoint