From b4197a226397ae8c7e9d214a349568073e45eed8 Mon Sep 17 00:00:00 2001
From: toaster <rollerorbital@gmail.com>
Date: Mon, 24 Jul 2023 23:40:30 +0100
Subject: [PATCH] Double-free emergency fix for virtual resources

- vres_GetMap guarantees the same memory for the same lump id, provided it's active
- vres_Free won't delete curmapvirt unless you do some silly temp pointer stuff
---
 src/p_setup.c | 11 +++++++++--
 src/p_setup.h |  1 +
 src/w_wad.c   | 12 ++++++++++++
 3 files changed, 22 insertions(+), 2 deletions(-)

diff --git a/src/p_setup.c b/src/p_setup.c
index 6ee45f218..ea2fb595d 100644
--- a/src/p_setup.c
+++ b/src/p_setup.c
@@ -8280,8 +8280,15 @@ boolean P_LoadLevel(boolean fromnetsave, boolean reloadinggamestate)
 	}
 
 	// Now safe to free.
-	vres_Free(curmapvirt);
-	curmapvirt = NULL;
+	// We do the following silly 
+	// construction because vres_Free
+	// no-sells deletions of pointers
+	// that are == curmapvirt.
+	{
+		virtres_t *temp = curmapvirt;
+		curmapvirt = NULL;
+		vres_Free(temp);
+	}
 
 	if (!reloadinggamestate)
 	{
diff --git a/src/p_setup.h b/src/p_setup.h
index fd343f927..e626363f4 100644
--- a/src/p_setup.h
+++ b/src/p_setup.h
@@ -35,6 +35,7 @@ extern boolean levelloading;
 extern UINT8 levelfadecol;
 
 extern lumpnum_t lastloadedmaplumpnum; // for comparative savegame
+extern virtres_t *curmapvirt;
 
 /* for levelflat type */
 enum
diff --git a/src/w_wad.c b/src/w_wad.c
index a2f249f3f..96fe606be 100644
--- a/src/w_wad.c
+++ b/src/w_wad.c
@@ -2354,6 +2354,12 @@ virtres_t* vres_GetMap(lumpnum_t lumpnum)
 	virtlump_t* vlumps = NULL;
 	size_t numlumps = 0;
 
+	if (lastloadedmaplumpnum == lumpnum && curmapvirt != NULL)
+	{
+		// Avoid duplicating all our hard work.
+		return curmapvirt;
+	}
+
 	if (W_IsLumpWad(lumpnum))
 	{
 		UINT32 realentry;
@@ -2430,6 +2436,12 @@ virtres_t* vres_GetMap(lumpnum_t lumpnum)
  */
 void vres_Free(virtres_t* vres)
 {
+	if (vres == curmapvirt)
+	{
+		// No-sell multiple references.
+		return;
+	}
+
 	while (vres->numlumps--)
 	{
 		if (vres->vlumps[vres->numlumps].data)