From 14bfc0be78c6eea825dacadf51dd1eaa4c64f4d9 Mon Sep 17 00:00:00 2001
From: JosJuice <josjuice@gmail.com>
Date: Fri, 5 Mar 2021 23:48:58 +0100
Subject: [PATCH] DiscIO: Fix reading certain WIA chunks with many exceptions

The loop in WIARVZFileReader::Chunk::Read could terminate
prematurely if the size argument was smaller than the size
of an exception list which had only been partially loaded.
---
 Source/Core/DiscIO/WIABlob.cpp | 16 +++++++++++-----
 Source/Core/DiscIO/WIABlob.h   |  2 ++
 2 files changed, 13 insertions(+), 5 deletions(-)

diff --git a/Source/Core/DiscIO/WIABlob.cpp b/Source/Core/DiscIO/WIABlob.cpp
index 8a76b9bd77..80baf6c677 100644
--- a/Source/Core/DiscIO/WIABlob.cpp
+++ b/Source/Core/DiscIO/WIABlob.cpp
@@ -653,7 +653,7 @@ bool WIARVZFileReader<RVZ>::Chunk::Read(u64 offset, u64 size, u8* out_ptr)
     return false;
   }
 
-  while (offset + size > m_out.bytes_written - m_out_bytes_used_for_exceptions)
+  while (offset + size > GetOutBytesWrittenExcludingExceptions())
   {
     u64 bytes_to_read;
     if (offset + size == m_out.data.size())
@@ -663,13 +663,13 @@ bool WIARVZFileReader<RVZ>::Chunk::Read(u64 offset, u64 size, u8* out_ptr)
     }
     else
     {
-      // Pick a suitable amount of compressed data to read. The std::min line has to
-      // be as it is, but the rest is a bit arbitrary and can be changed if desired.
+      // Pick a suitable amount of compressed data to read. We have to ensure that bytes_to_read
+      // is larger than 0 and smaller than or equal to the number of bytes available to read,
+      // but the rest is a bit arbitrary and could be changed.
 
       // The compressed data is probably not much bigger than the decompressed data.
       // Add a few bytes for possible compression overhead and for any hash exceptions.
-      bytes_to_read =
-          offset + size - (m_out.bytes_written - m_out_bytes_used_for_exceptions) + 0x100;
+      bytes_to_read = offset + size - GetOutBytesWrittenExcludingExceptions() + 0x100;
 
       // Align the access in an attempt to gain speed. But we don't actually know the
       // block size of the underlying storage device, so we just use the Wii block size.
@@ -839,6 +839,12 @@ void WIARVZFileReader<RVZ>::Chunk::GetHashExceptions(
                                                               m_in_bytes_used_for_exceptions));
 }
 
+template <bool RVZ>
+size_t WIARVZFileReader<RVZ>::Chunk::GetOutBytesWrittenExcludingExceptions() const
+{
+  return m_exception_lists == 0 ? m_out.bytes_written - m_out_bytes_used_for_exceptions : 0;
+}
+
 template <bool RVZ>
 bool WIARVZFileReader<RVZ>::ApplyHashExceptions(
     const std::vector<HashExceptionEntry>& exception_list,
diff --git a/Source/Core/DiscIO/WIABlob.h b/Source/Core/DiscIO/WIABlob.h
index d6e54df7ac..8458ac95ee 100644
--- a/Source/Core/DiscIO/WIABlob.h
+++ b/Source/Core/DiscIO/WIABlob.h
@@ -202,6 +202,8 @@ private:
     bool HandleExceptions(const u8* data, size_t bytes_allocated, size_t bytes_written,
                           size_t* bytes_used, bool align);
 
+    size_t GetOutBytesWrittenExcludingExceptions() const;
+
     DecompressionBuffer m_in;
     DecompressionBuffer m_out;
     size_t m_in_bytes_read = 0;