From af93d819c62a930cf3ed2061355b422c5ce4e7c3 Mon Sep 17 00:00:00 2001
From: Adrian-Stefan Mares <36161392+adriansmares@users.noreply.github.com>
Date: Sat, 20 Apr 2024 03:56:48 +0200
Subject: [PATCH] Handle `INVALID_FUNCTION` mismatches at plugin boundaries,
 redux (#2136)

---
 core/logic/smn_datapacks.cpp   | 21 +++++++++++++++++++--
 core/logic/smn_fakenatives.cpp | 29 ++++++++++++++++++++++++++++-
 core/logic/smn_functions.cpp   | 30 +++++++++++++++++++++---------
 3 files changed, 68 insertions(+), 12 deletions(-)

diff --git a/core/logic/smn_datapacks.cpp b/core/logic/smn_datapacks.cpp
index 3276c30086..9cf2a4a323 100644
--- a/core/logic/smn_datapacks.cpp
+++ b/core/logic/smn_datapacks.cpp
@@ -244,7 +244,19 @@ static cell_t smn_WritePackFunction(IPluginContext *pContext, const cell_t *para
 		pDataPack->RemoveItem();
 	}
 
-	pDataPack->PackFunction(params[2]);
+	cell_t funcid = params[2];
+	if (pContext->IsNullFunctionId(funcid))
+	{
+		pDataPack->PackFunction(0);
+	} 
+	else if (funcid <= 0)
+	{
+		return pContext->ThrowNativeError("Invalid function id (%X)", funcid);
+	}
+	else
+	{
+		pDataPack->PackFunction(funcid);
+	}
 
 	return 1;
 }
@@ -365,7 +377,12 @@ static cell_t smn_ReadPackFunction(IPluginContext *pContext, const cell_t *param
 		return pContext->ThrowNativeError("Invalid data pack type (got %d / expected %d).", pDataPack->GetCurrentType(), CDataPackType::Function);
 	}
 
-	return pDataPack->ReadFunction();
+	cell_t funcid = pDataPack->ReadFunction();
+	if (!funcid)
+	{
+		return pContext->GetNullFunctionValue();
+	}
+	return funcid;
 }
 
 static cell_t smn_ReadPackCellArray(IPluginContext *pContext, const cell_t *params)
diff --git a/core/logic/smn_fakenatives.cpp b/core/logic/smn_fakenatives.cpp
index cbbca65e86..e68e527a6d 100644
--- a/core/logic/smn_fakenatives.cpp
+++ b/core/logic/smn_fakenatives.cpp
@@ -366,6 +366,33 @@ static cell_t SetNativeArray(IPluginContext *pContext, const cell_t *params)
 	return SP_ERROR_NONE;
 }
 
+static cell_t GetNativeFunction(IPluginContext *pContext, const cell_t *params)
+{
+	if (!s_curnative || (s_curnative->ctx != pContext))
+	{
+		return pContext->ThrowNativeError("Not called from inside a native function");
+	}
+
+	cell_t param = params[1];
+	if (param < 1 || param > s_curparams[0])
+	{
+		return pContext->ThrowNativeErrorEx(SP_ERROR_PARAM, "Invalid parameter number: %d", param);
+	}
+	
+	cell_t funcid = s_curparams[param];
+	if (s_curcaller->IsNullFunctionId(funcid))
+	{
+		// see alliedmodders/sourcepawn#912, alliedmodders/sourcemod#2068
+		// convert null function to receiver's expected value so equality checks against INVALID_FUNCTION pass
+		return pContext->GetNullFunctionValue();
+	}
+	else if (funcid <= 0)
+	{
+		return pContext->ThrowNativeError("Invalid function id (%X)", funcid);
+	}
+	return funcid;
+}
+
 static cell_t FormatNativeString(IPluginContext *pContext, const cell_t *params)
 {
 	if (!s_curnative || (s_curnative->ctx != pContext))
@@ -483,7 +510,7 @@ REGISTER_NATIVES(nativeNatives)
 	{"GetNativeArray",			GetNativeArray},
 	{"GetNativeCell",			GetNativeCell},
 	{"GetNativeCellRef",		GetNativeCellRef},
-	{"GetNativeFunction",       GetNativeCell},
+	{"GetNativeFunction",       GetNativeFunction},
 	{"GetNativeString",			GetNativeString},
 	{"GetNativeStringLength",	GetNativeStringLength},
 	{"FormatNativeString",		FormatNativeString},
diff --git a/core/logic/smn_functions.cpp b/core/logic/smn_functions.cpp
index ea1acaba78..41349f96ee 100644
--- a/core/logic/smn_functions.cpp
+++ b/core/logic/smn_functions.cpp
@@ -228,11 +228,15 @@ static cell_t sm_AddToForward(IPluginContext *pContext, const cell_t *params)
 		}
 	}
 
-	IPluginFunction *pFunction = pPlugin->GetBaseContext()->GetFunctionById(params[3]);
-
+	cell_t funcid = params[3];
+	if (funcid <= 0)
+	{
+		return pContext->ThrowNativeError("Invalid function id (%X)", funcid);
+	}
+	IPluginFunction *pFunction = pPlugin->GetBaseContext()->GetFunctionById(funcid);
 	if (!pFunction)
 	{
-		return pContext->ThrowNativeError("Invalid function id (%X)", params[3]);
+		return pContext->ThrowNativeError("Invalid function id (%X)", funcid);
 	}
 
 	return pForward->AddFunction(pFunction);
@@ -265,11 +269,15 @@ static cell_t sm_RemoveFromForward(IPluginContext *pContext, const cell_t *param
 		}
 	}
 
-	IPluginFunction *pFunction = pPlugin->GetBaseContext()->GetFunctionById(params[3]);
-
+	cell_t funcid = params[3];
+	if (funcid <= 0)
+	{
+		return pContext->ThrowNativeError("Invalid function id (%X)", funcid);
+	}
+	IPluginFunction *pFunction = pPlugin->GetBaseContext()->GetFunctionById(funcid);
 	if (!pFunction)
 	{
-		return pContext->ThrowNativeError("Invalid function id (%X)", params[3]);
+		return pContext->ThrowNativeError("Invalid function id (%X)", funcid);
 	}
 
 	return pForward->RemoveFunction(pFunction);
@@ -327,11 +335,15 @@ static cell_t sm_CallStartFunction(IPluginContext *pContext, const cell_t *param
 		}
 	}
 
-	s_pFunction = pPlugin->GetBaseContext()->GetFunctionById(params[2]);
-
+	cell_t funcid = params[2];
+	if (funcid <= 0)
+	{
+		return pContext->ThrowNativeError("Invalid function id (%X)", funcid);
+	}
+	s_pFunction = pPlugin->GetBaseContext()->GetFunctionById(funcid);
 	if (!s_pFunction)
 	{
-		return pContext->ThrowNativeError("Invalid function id (%X)", params[2]);
+		return pContext->ThrowNativeError("Invalid function id (%X)", funcid);
 	}
 
 	s_pCallable = static_cast<ICallable *>(s_pFunction);