util.c: add and use ascii-only char functions

The "invalid_name" function claims to "allow strict ASCII letters and
numbers".

However, it uses isalnum(3) and isdigit(3), which may take the current
locale into account and thus return 1 for non-ASCII characters.

So add the following functions:

* ascii_isalnum
* ascii_isalpha
* ascii_isdigit
* ascii_islower
* ascii_isupper
* ascii_isxdigit

And use the applicable ones in "invalid_name" so that it actually uses
strictly ASCII in its comparisons.

Added on commit b4ffaa207 ("merges; more on cleaning up esc chars",
2023-02-14).

Relates to #5578.

Kind of relates to #5708.

1 files changed, 29 insertions, 2 deletions

diff --git a/src/firejail/util.c b/src/firejail/util.c
index cda99e432..b2a0c85f1 100644
--- a/src/firejail/util.c
+++ b/src/firejail/util.c
@@ -1448,15 +1448,42 @@ static int has_link(const char *dir) {
         return 0;
 }
 
+int ascii_isalnum(unsigned char c) {
+        return (ascii_isalpha(c) || ascii_isdigit(c));
+}
+
+int ascii_isalpha(unsigned char c) {
+        return (ascii_islower(c) || ascii_isupper(c));
+}
+
+int ascii_isdigit(unsigned char c) {
+        return (c >= '0' && c <= '9');
+}
+
+int ascii_islower(unsigned char c) {
+        return (c >= 'a' && c <= 'z');
+}
+
+int ascii_isupper(unsigned char c) {
+        return (c >= 'A' && c <= 'Z');
+}
+
+int ascii_isxdigit(unsigned char c) {
+        int ret = (ascii_isdigit(c) ||
+                  (c >= 'a' && c <= 'f') ||
+                  (c >= 'A' && c <= 'F'));
+        return ret;
+}
+
 // allow strict ASCII letters and numbers; names with only numbers are rejected; spaces are rejected
 int invalid_name(const char *name) {
         const char *c = name;
 
         int only_numbers = 1;
         while (*c) {
-                if (!isalnum(*c))
+                if (!ascii_isalnum(*c))
                         return 1;
-                if (!isdigit(*c))
+                if (!ascii_isdigit(*c))
                         only_numbers = 0;
                 ++c;
         }