Fix crash in CPathFind path node loader when allocation fails

Client/game_sa/HookSystem.h

@@ -74,6 +74,24 @@ bool HookInstall(DWORD dwInstallAddress, T dwHookHandler, int iJmpCodeSize = 5)
     }
 }
 
+// For install addresses outside the ranges MemCpy knows how to unprotect; the page must have
+// been made writable beforehand (see SetInitialVirtualProtect)
+template <typename T>
+bool HookInstallFast(DWORD dwInstallAddress, T dwHookHandler, int iJmpCodeSize = 5)
+{
+    BYTE JumpBytes[MAX_JUMPCODE_SIZE];
+    MemSetFast(JumpBytes, 0x90, MAX_JUMPCODE_SIZE);
+    if (CreateJump(dwInstallAddress, (DWORD)FunctionPointerToVoidP(dwHookHandler), JumpBytes))
+    {
+        MemCpyFast((PVOID)dwInstallAddress, JumpBytes, iJmpCodeSize);
+        return true;
+    }
+    else
+    {
+        return false;
+    }
+}
+
 // Auto detect requirement of US/EU hook installation
 #define EZHookInstall(type) HookInstall(HOOKPOS_##type, (DWORD)HOOK_##type, HOOKSIZE_##type);
 

Client/multiplayer_sa/CMultiplayerSA_CrashFixHacks.cpp

@@ -4092,6 +4092,40 @@ static int _cdecl CFileLoader_LoadVehicleObject_sscanf(const char* s, const char
                   rearWheelSize, wheelUpgradeClass);
 }
 
+//////////////////////////////////////////////////////////////////////////////////////////
+//
+// CPathFind's per map area path node loader calls malloc() for m_pPathNodes[area] (offset
+// 0x804) without checking the result, then loops over it using m_dwNumNodes[area] (offset
+// 0xfa4) as the count. If the allocation fails, that loop dereferences a null pointer and
+// crashes.
+//
+// Right where the node count gets loaded for the loop's bound check, this hook also checks
+// whether m_pPathNodes[area] is null, and if so forces the count to 0 so the loop is skipped.
+//
+//////////////////////////////////////////////////////////////////////////////////////////
+#define HOOKPOS_CPathFind_LoadPathNodeCount_Mid  0x0156F966
+#define HOOKSIZE_CPathFind_LoadPathNodeCount_Mid 7
+DWORD                         RETURN_CPathFind_LoadPathNodeCount_Mid = 0x0156F96D;
+static void __declspec(naked) HOOK_CPathFind_LoadPathNodeCount_Mid()
+{
+    MTA_VERIFY_HOOK_LOCAL_SIZE;
+
+    // clang-format off
+    __asm
+    {
+        // Replicate the overwritten instruction: EAX = m_dwNumNodes[area]
+        mov     eax, dword ptr [esi + edi*4 + 0x0fa4]
+
+        // If m_pPathNodes[area] failed to allocate, force the node count to 0 for this loop
+        cmp     dword ptr [esi + edi*4 + 0x804], 0
+        jne     nodesOk
+        xor     eax, eax
+        nodesOk:
+        jmp     RETURN_CPathFind_LoadPathNodeCount_Mid
+    }
+    // clang-format on
+}
+
 //////////////////////////////////////////////////////////////////////////////////////////
 //
 // Setup hooks for CrashFixHacks
@@ -4191,4 +4225,9 @@ void CMultiplayerSA::InitHooks_CrashFixHacks()
 
     // Fix uninitialized wheel scale in CFileLoader::LoadVehicleObject on Win11 24H2
     HookInstallCall(CALL_CFileLoader_LoadVehicleObject_sscanf, (DWORD)CFileLoader_LoadVehicleObject_sscanf);
+
+    // This address sits further into the executable than EZHookInstall's normal range check
+    // allows, so it is installed with HookInstallFast instead; the page is unprotected up front
+    // in SetInitialVirtualProtect
+    HookInstallFast(HOOKPOS_CPathFind_LoadPathNodeCount_Mid, (DWORD)HOOK_CPathFind_LoadPathNodeCount_Mid, HOOKSIZE_CPathFind_LoadPathNodeCount_Mid);
 }

Shared/sdk/SharedUtil.MemAccess.hpp

@@ -49,6 +49,9 @@ namespace SharedUtil
         VirtualProtect((LPVOID)0x6AE000, 0x1000, PAGE_EXECUTE_READWRITE, &oldProt);
         VirtualProtect((LPVOID)0x729000, 0x1000, PAGE_EXECUTE_READWRITE, &oldProt);
         VirtualProtect((LPVOID)0x742000, 0x1000, PAGE_EXECUTE_READWRITE, &oldProt);
+
+        // Used by the CPathFind crash fix in multiplayer_sa/CMultiplayerSA_CrashFixHacks.cpp, installed via the Fast path.
+        VirtualProtect((LPVOID)0x156F000, 0x1000, PAGE_EXECUTE_READWRITE, &oldProt);
     }
 
     // Returns true if pAddr is in slow mem area