From e9e2504bf4c49b17c0c8981cd761b90080426ccf Mon Sep 17 00:00:00 2001
From: Bram Matthys <syzop@vulnscan.org>
Date: Fri, 25 Jun 2021 11:16:12 +0200
Subject: [PATCH] Don't allow remote servers to write to our MD client objects
 by default.

Modules can still opt-in via mreq.remote_write=1 to allow it for
certain moddata.
For example, k4be may want to do this for his geoip-base module which
allows a single server to set moddata "geoip" for all connecting clients,
including remote clients.
If you are a moddata provider then you can enable it like this:
 ModDataInfo mreq;
 [..]
 #if UNREAL_VERSION_TIME >= 202125
 mreq.remote_write = 1;
 #endif
 [..]

See discussion on https://github.com/unrealircd/unrealircd/pull/142
---
 include/modules.h |  1 +
 include/version.h |  2 +-
 src/api-moddata.c |  1 +
 src/modules/md.c  | 22 ++++++++++++++++++++++
 4 files changed, 25 insertions(+), 1 deletion(-)

diff --git a/include/modules.h b/include/modules.h
index 5bd22ec8d..e446b6beb 100644
--- a/include/modules.h
+++ b/include/modules.h
@@ -151,6 +151,7 @@ struct ModDataInfo {
 	char *(*serialize)(ModData *m); /**< Function which converts the data to a string. May return NULL if 'm' contains no data (since for example m->ptr may be NULL). */
 	void (*unserialize)(char *str, ModData *m); /**< Function which converts the string back to data */
 	int sync; /**< Send in netsynch (when servers connect) */
+	int remote_write; /**< Allow remote servers to set/unset this moddata, even if it they target one of our own clients */
 };
 
 #define moddata_client(acptr, md)    acptr->moddata[md->slot]
diff --git a/include/version.h b/include/version.h
index 281fdf93b..9e44370ae 100644
--- a/include/version.h
+++ b/include/version.h
@@ -54,7 +54,7 @@
  * Can be useful if the above 3 versionids are insufficient for you (eg: you want to support CVS).
  * This is updated automatically on the CVS server every Monday. so don't touch it.
  */
-#define UNREAL_VERSION_TIME	202120
+#define UNREAL_VERSION_TIME	202125
 
 #define UnrealProtocol 		5002
 #define PATCH1  		macro_to_str(UNREAL_VERSION_GENERATION)
diff --git a/src/api-moddata.c b/src/api-moddata.c
index 84be03b74..919bce8fb 100644
--- a/src/api-moddata.c
+++ b/src/api-moddata.c
@@ -80,6 +80,7 @@ moddataadd_isok:
 	m->serialize = req.serialize;
 	m->unserialize = req.unserialize;
 	m->sync = req.sync;
+	m->remote_write = req.remote_write;
 	m->owner = module;
 	
 	if (new_struct)
diff --git a/src/modules/md.c b/src/modules/md.c
index 485e8a4b0..0ac8e3a82 100644
--- a/src/modules/md.c
+++ b/src/modules/md.c
@@ -105,6 +105,14 @@ CMD_FUNC(cmd_md)
 		md = findmoddata_byname(varname, MODDATATYPE_CLIENT);
 		if (!md || !md->unserialize || !target)
 			return;
+
+		if (MyConnect(target) && !md->remote_write)
+		{
+			ircd_log(LOG_ERROR, "Remote server '%s' tried to write moddata '%s' of a client from ours '%s' -- attempt blocked.",
+			         client->name, md->name, target->name);
+			return;
+		}
+
 		if (value)
 			md->unserialize(value, &moddata_client(target, md));
 		else
@@ -162,6 +170,13 @@ CMD_FUNC(cmd_md)
 		if (!md || !md->unserialize)
 			return;
 
+		if (MyConnect(target) && !md->remote_write)
+		{
+			ircd_log(LOG_ERROR, "Remote server '%s' tried to write moddata '%s' of a client from ours '%s' -- attempt blocked.",
+			         client->name, md->name, target->name);
+			return;
+		}
+
 		if (value)
 			md->unserialize(value, &moddata_member(m, md));
 		else
@@ -202,6 +217,13 @@ CMD_FUNC(cmd_md)
 		if (!md || !md->unserialize)
 			return;
 
+		if (MyConnect(target) && !md->remote_write)
+		{
+			ircd_log(LOG_ERROR, "Remote server '%s' tried to write moddata '%s' of a client from ours '%s' -- attempt blocked.",
+			         client->name, md->name, target->name);
+			return;
+		}
+
 		if (value)
 			md->unserialize(value, &moddata_membership(m, md));
 		else