From ed9fcb842ed381d112f09ef3af1036033d5f22bc Mon Sep 17 00:00:00 2001
From: mckaygerhard <mckaygerhard@gmail.com>
Date: Sun, 17 Sep 2023 20:07:12 -0400
Subject: [PATCH] antihacks: Patch fast/teleport vulnerability when attached to
 an entity

* backported https://github.com/minetest/minetest/pull/10340/commits
* Fixed God Mode
* use core::radToDeg and a single v3f to multiply attachment_pos with
* Use getLength() for diffvec
---
 src/content_sao.cpp | 24 +++++++++++++++++++++++-
 1 file changed, 23 insertions(+), 1 deletion(-)

diff --git a/src/content_sao.cpp b/src/content_sao.cpp
index 278dd0df6..8fad8ad11 100644
--- a/src/content_sao.cpp
+++ b/src/content_sao.cpp
@@ -1372,12 +1372,34 @@ std::string PlayerSAO::getPropertyPacket()
 
 bool PlayerSAO::checkMovementCheat()
 {
-	if (isAttached() || m_is_singleplayer ||
+	if (m_is_singleplayer ||
 			g_settings->getBool("disable_anticheat")) {
 		m_last_good_position = m_base_position;
 		return false;
 	}
+	if (UnitSAO *parent = dynamic_cast<UnitSAO *>(getParent())) {
+		v3f attachment_pos;
+		{
+			int parent_id;
+			std::string bone;
+			v3f attachment_rot;
+			getAttachment(&parent_id, &bone, &attachment_pos, &attachment_rot);
+		}
 
+		v3f parent_pos = parent->getBasePosition();
+		f32 diff = m_base_position.getDistanceFromSQ(parent_pos) - attachment_pos.getLengthSQ();
+		const f32 maxdiff = 4.0f * BS; // fair trade-off value for various latencies
+
+		if (diff > maxdiff * maxdiff) {
+			setBasePosition(parent_pos);
+			actionstream << "Server: " << m_player->getName()
+					<< " moved away from parent; diff=" << sqrtf(diff) / BS
+					<< " resetting position." << std::endl;
+			return true;
+		}
+		// Player movement is locked to the entity. Skip further checks
+		return false;
+	}
 	bool cheated = false;
 	/*
 		Check player movements