[gnome-initial-setup/gbsneto/accounts-crash-bug] accounts: Also check against NAME_REGEX if provided

[Georges Basile Stavracas Neto <gbsneto src gnome org>]

commit 835236d37561580bece0380d52188b89643f686d
Author: Georges Basile Stavracas Neto <georges stavracas gmail com>
Date:   Wed Jul 27 14:58:00 2022 -0300

    accounts: Also check against NAME_REGEX if provided
    
    In addition to checking if each character of the proposed username
    conforms to UNIX concentions, if /etc/adduser.conf is present and
    it provides NAME_REGEX, try and match the username against this
    regex too.
    
    This should fix cases where Initial Setup thinks the password is
    okay, but accountsservice rejects the proposed username.
    
    To make error reporting decent, check if the provided regex is the
    lowercase-only regex, which is probably the most common one.

 gnome-initial-setup/pages/account/um-utils.c | 70 +++++++++++++++++++++++++++-
 1 file changed, 68 insertions(+), 2 deletions(-)
---
diff --git a/gnome-initial-setup/pages/account/um-utils.c b/gnome-initial-setup/pages/account/um-utils.c
index 39887498..b60cf8f3 100644
--- a/gnome-initial-setup/pages/account/um-utils.c
+++ b/gnome-initial-setup/pages/account/um-utils.c
@@ -106,9 +106,58 @@ is_valid_name (const gchar *name)
         return !is_empty;
 }
 
+#define LOWERCASE_ONLY_REGEX "^[a-z][-a-z0-9_]*$"
+
+static GRegex*
+get_adduser_regex (gboolean *out_is_lowercase_only)
+{
+        static gboolean lowercase_only = FALSE;
+        static gboolean initialized = FALSE;
+        static GRegex *adduser_regex = NULL;
+
+        if (!initialized) {
+                g_autofree gchar *contents = NULL;
+
+                if (g_file_get_contents ("/etc/adduser.conf", &contents, NULL, NULL)) {
+                        g_auto(GStrv) lines = g_strsplit (contents, "\n", -1);
+                        gsize i;
+
+                        for (i = 0; lines && lines[i] != NULL; i++) {
+                                g_autofree gchar *unquoted = NULL;
+                                gchar *line = g_strstrip (lines[i]);
+
+                                if (*line == '#' || !g_str_has_prefix (line, "NAME_REGEX="))
+                                        continue;
+
+                                line += strlen ("NAME_REGEX=");
+                                unquoted = g_shell_unquote (line, NULL);
+
+                                if (!unquoted)
+                                        continue;
+
+                                adduser_regex = g_regex_new (unquoted,
+                                                             G_REGEX_OPTIMIZE,
+                                                             0,
+                                                             NULL);
+
+                                /* This comes from Debian regex */
+                                lowercase_only = g_str_equal (unquoted, LOWERCASE_ONLY_REGEX);
+                                break;
+                        }
+                }
+
+                initialized = TRUE;
+        }
+
+        *out_is_lowercase_only = lowercase_only;
+        return adduser_regex;
+}
+
 gboolean
 is_valid_username (const gchar *username, gboolean parental_controls_enabled, gchar **tip)
 {
+        gboolean adduser_regex_valid;
+        gboolean lowecase_only;
         gboolean empty;
         gboolean in_use;
         gboolean too_long;
@@ -125,25 +174,36 @@ is_valid_username (const gchar *username, gboolean parental_controls_enabled, gc
                 in_use = is_username_used (username);
                 too_long = strlen (username) > MAXNAMELEN;
         }
+        adduser_regex_valid = TRUE;
+        lowecase_only = FALSE;
         valid = TRUE;
 
         if (!in_use && !empty && !too_long) {
+                GRegex *adduser_regex = get_adduser_regex (&lowecase_only);
+
                 /* First char must be a letter, and it must only composed
                  * of ASCII letters, digits, and a '.', '-', '_'
                  */
                 for (c = username; *c; c++) {
                         if (! ((*c >= 'a' && *c <= 'z') ||
-                               (*c >= 'A' && *c <= 'Z') ||
+                               (!lowecase_only && (*c >= 'A' && *c <= 'Z')) ||
                                (*c >= '0' && *c <= '9') ||
                                (*c == '_') || (*c == '.') ||
                                (*c == '-' && c != username)))
                            valid = FALSE;
                 }
+
+                /* Second, if useradd.conf provides a regex for username
+                 * validation, use it.
+                 */
+                if (valid && adduser_regex)
+                        adduser_regex_valid = g_regex_match (adduser_regex, username, 0, NULL);
+
         }
 
         parental_controls_conflict = (parental_controls_enabled && g_strcmp0 (username, "administrator") == 
0);
 
-        valid = !empty && !in_use && !too_long && !parental_controls_conflict && valid;
+        valid = !empty && !in_use && !too_long && !parental_controls_conflict && adduser_regex_valid && 
valid;
 
         if (!empty && (in_use || too_long || parental_controls_conflict || !valid)) {
                 if (in_use) {
@@ -158,6 +218,12 @@ is_valid_username (const gchar *username, gboolean parental_controls_enabled, gc
                 else if (parental_controls_conflict) {
                         *tip = g_strdup (_("That username isn’t available. Please try another."));
                 }
+                else if (!adduser_regex_valid && !lowecase_only) {
+                        *tip = g_strdup (_("The username does not conform to the system policies. Contact 
your system administrator."));
+                }
+                else if (lowecase_only) {
+                        *tip = g_strdup (_("The username should only consist of lower case letters from a-z, 
digits and the following characters: . - _"));
+                }
                 else {
                         *tip = g_strdup (_("The username should only consist of upper and lower case letters 
from a-z, digits and the following characters: . - _"));
                 }