misc-progs: Add functions to sanitise input arguments

Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>

src/misc-progs/setuid.c

@@ -199,3 +199,42 @@ int initsetuid(void) {
 
 	return 1;
 }
+
+/* Checks if a string only contains alphanumerical characters, dash or underscore */
+int is_valid_argument_alnum(const char* arg) {
+	size_t l = strlen(arg);
+
+	for (unsigned int i = 0; i < l; i++) {
+		char c = arg[i];
+
+		// Dash or underscore
+		if (c == '-' || c == '_')
+			continue;
+
+		// Any alphanumerical character
+		if (isalnum(c))
+			continue;
+
+		// Invalid
+		return 0;
+	}
+
+	return 1;
+}
+
+int is_valid_argument_num(const char* arg) {
+	size_t l = strlen(arg);
+
+	for (unsigned int i = 0; i < l; i++) {
+		char c = arg[i];
+
+		// Any digit
+		if (isdigit(c))
+			continue;
+
+		// Invalid
+		return 0;
+	}
+
+	return 1;
+}

src/misc-progs/setuid.h

@@ -33,6 +33,9 @@ int safe_system(char* command);
 int unpriv_system(char* command, uid_t uid, gid_t gid);
 int initsetuid(void);
 
+int is_valid_argument_alnum(const char* arg);
+int is_valid_argument_num(const char* arg);
+
 /* Compatibility for the local copy of strlcat,
  * which has been removed. */
 #define strlcat(src, dst, size) strncat(src, dst, size)