From da2a27ef056a0179cbd80f9146e58b89403d9933 Mon Sep 17 00:00:00 2001
From: DRC <information@libjpeg-turbo.org>
Date: Sat, 18 Mar 2017 16:15:14 -0500
Subject: [PATCH] Honor max_memory_to_use/JPEGMEM/-maxmemory

This re-introduces a feature of the obsolete system-specific libjpeg
memory managers-- namely the ability to limit the amount of main memory
used by the library during decompression or multi-pass compression.
This is mainly beneficial for two reasons:

- Works around a 2 GB limit in libFuzzer
- Allows security-sensitive applications to set a memory limit for the
  JPEG decoder so as to work around the progressive JPEG exploit
  (LJT-01-004) described here:
  http://www.libjpeg-turbo.org/pmwiki/uploads/About/TwoIssueswiththeJPEGStandard.pdf

This commit also removes obsolete documentation regarding the MS-DOS
memory manager (which itself was removed long ago) and changes the
documentation of the -maxmemory switch and JPEGMEM environment variable
to reflect the fact that backing stores are never used in libjpeg-turbo.

Inspired by:
https://github.com/caolanm/libjpeg-turbo/commit/066fee2e7d6834f24838bc1896aa38ca77209e3c

Closes #143
---
 ChangeLog.md  | 15 +++++++++++++++
 cjpeg.1       |  4 ++--
 djpeg.1       |  4 ++--
 jmemnobs.c    | 16 +++++++++++-----
 jpegtran.1    |  4 ++--
 libjpeg.txt   | 14 ++++++--------
 structure.txt | 24 +++++++++++-------------
 usage.txt     | 35 +++++------------------------------
 8 files changed, 54 insertions(+), 62 deletions(-)

diff --git a/jmemnobs.c b/jmemnobs.c
index 5797198..ac12afa 100644
--- a/jmemnobs.c
+++ b/jmemnobs.c
@@ -3,8 +3,8 @@
  *
  * This file was part of the Independent JPEG Group's software:
  * Copyright (C) 1992-1996, Thomas G. Lane.
- * It was modified by The libjpeg-turbo Project to include only code and
- * information relevant to libjpeg-turbo.
+ * libjpeg-turbo Modifications:
+ * Copyright (C) 2017, D. R. Commander.
  * For conditions of distribution and use, see the accompanying README.ijg
  * file.
  *
@@ -15,7 +15,6 @@
  * This is very portable in the sense that it'll compile on almost anything,
  * but you'd better have lots of main memory (or virtual memory) if you want
  * to process big images.
- * Note that the max_memory_to_use option is ignored by this implementation.
  */
 
 #define JPEG_INTERNALS
@@ -66,14 +65,21 @@ jpeg_free_large (j_common_ptr cinfo, void *object, size_t sizeofobject)
 
 /*
  * This routine computes the total memory space available for allocation.
- * Here we always say, "we got all you want bud!"
  */
 
 GLOBAL(size_t)
 jpeg_mem_available (j_common_ptr cinfo, size_t min_bytes_needed,
                     size_t max_bytes_needed, size_t already_allocated)
 {
-  return max_bytes_needed;
+  if (cinfo->mem->max_memory_to_use) {
+    if (cinfo->mem->max_memory_to_use > already_allocated)
+      return cinfo->mem->max_memory_to_use - already_allocated;
+    else
+      return 0;
+  } else {
+    /* Here we always say, "we got all you want bud!" */
+    return max_bytes_needed;
+  }
 }