Add extban type for unidentified connections (#411)

* Add extension extb_guest

This module provides an extban type that acts as a normal ban but
only matches unidentified users.

* Document extban g in help/opers/extban

* extensions/extb_guest: support CIDR masks in $g extbans

This allows a channel operator to set a channel ban such as
"$g:*!*@192.0.2.0/24#*web.libera.chat*" and have it function
as intended.

---------

Co-authored-by: Aaron Jones <me@aaronmdjones.net>

extensions/Makefile.am

@@ -19,6 +19,7 @@ extension_LTLIBRARIES =		\
   extb_account.la		\
   extb_canjoin.la		\
   extb_channel.la		\
+	extb_guest.la		\
   extb_hostmask.la		\
   extb_oper.la			\
   extb_server.la		\

extensions/README

@@ -79,6 +79,7 @@ extb_account.so  - Account bans (+b $a[:mask])
 extb_canjoin.so  - Banned from another channel (+b $j:mask)
 extb_channel.so  - Other-channel bans (+b $c:mask)
 extb_extgecos.so - Extended ban (+b $x:mask)
+extb_guest.so    - Unidentified bans (+b $g:mask)
 extb_oper.so     - Oper bans (+b $o)
 extb_realname.so - Realname (gecos) bans (+b $r:mask)
 extb_server.so   - Server bans (+b $s:mask)

extensions/extb_guest.c

@@ -0,0 +1,73 @@
+/*
+ * Guest extban type: bans unidentified users matching nick!user@host.
+ * -- TheDaemoness
+ */
+
+#include "stdinc.h"
+#include "modules.h"
+#include "client.h"
+#include "ircd.h"
+
+static const char extb_desc[] = "Guest ($g) extban type - bans unidentified users matching nick!user@host";
+
+static int _modinit(void);
+static void _moddeinit(void);
+static int eb_guest(const char *data, struct Client *client_p, struct Channel *chptr, long mode_type);
+
+DECLARE_MODULE_AV2(extb_guest, _modinit, _moddeinit, NULL, NULL, NULL, NULL, NULL, extb_desc);
+
+static int
+_modinit(void)
+{
+	extban_table['g'] = eb_guest;
+
+	return 0;
+}
+
+static void
+_moddeinit(void)
+{
+	extban_table['g'] = NULL;
+}
+
+static int eb_guest(const char *data, struct Client *client_p,
+		struct Channel *chptr, long mode_type)
+{
+	(void)chptr;
+
+	if (data == NULL)
+		return EXTBAN_INVALID;
+
+	const char *idx = strchr(data, '#');
+
+	if (idx != NULL && idx[1] == '\0')
+		/* Users cannot have empty realnames,
+		 * so don't let a ban be set matching one
+		 */
+		return EXTBAN_INVALID;
+
+	if (!EmptyString(client_p->user->suser))
+		return EXTBAN_NOMATCH;
+
+	if (idx != NULL)
+	{
+		char buf[BUFSIZE];
+
+		// Copy the nick!user@host part of the ban
+		memcpy(buf, data, (idx - data));
+		buf[(idx - data)] = '\0';
+
+		// Advance to the realname part of the ban
+		idx++;
+
+		if (client_matches_mask(client_p, buf) && match(idx, client_p->info))
+			return EXTBAN_MATCH;
+
+		return EXTBAN_NOMATCH;
+	}
+
+	if (client_matches_mask(client_p, data))
+		return EXTBAN_MATCH;
+
+	return EXTBAN_NOMATCH;
+}

help/opers/extban

@@ -19,6 +19,7 @@ Unless noted below, all types can be used with +b, +q, +e and +I.
   $a:<mask> - Matches users logged in with a username matching the mask
               (* and ? wildcards)
   $c:<chan> - Matches users who are on the given channel
+  $g:<mask> - Matches as a normal ban but excludes logged in users
      $o     - Matches opers (most useful with +I)
   $r:<mask> - Matches users with a realname (gecos) matching the mask
               (* and ? wildcards); this can only be used with +b and +q