rdppm.c: Fix buf overrun caused by bad binary PPM

This extends the fix in 1e81b0c to
include binary PPM files with maximum values < 255, thus preventing a
malformed binary PPM input file with those specifications from
triggering an overrun of the rescale array and potentially crashing
cjpeg, TJBench, or any program that uses the tjLoadImage() function.

Fixes #433

ChangeLog.md

@@ -13,6 +13,12 @@ TurboJPEG Java API that caused an error ("java.lang.IllegalStateException: No
 source image is associated with this instance") when attempting to use that
 method to compress a YUV image.
 
+3. Fixed an issue in the PPM reader that caused a buffer overrun in cjpeg,
+TJBench, or the `tjLoadImage()` function if one of the values in a binary
+PPM/PGM input file exceeded the maximum value defined in the file's header and
+that maximum value was less than 255.  libjpeg-turbo 1.5.0 already included a
+similar fix for binary PPM/PGM files with maximum values greater than 255.
+
 
 2.0.4
 =====
@@ -578,10 +584,10 @@ application was linked against.
 
 3. Fixed a couple of issues in the PPM reader that would cause buffer overruns
 in cjpeg if one of the values in a binary PPM/PGM input file exceeded the
-maximum value defined in the file's header.  libjpeg-turbo 1.4.2 already
-included a similar fix for ASCII PPM/PGM files.  Note that these issues were
-not security bugs, since they were confined to the cjpeg program and did not
-affect any of the libjpeg-turbo libraries.
+maximum value defined in the file's header and that maximum value was greater
+than 255.  libjpeg-turbo 1.4.2 already included a similar fix for ASCII PPM/PGM
+files.  Note that these issues were not security bugs, since they were confined
+to the cjpeg program and did not affect any of the libjpeg-turbo libraries.
 
 4. Fixed an issue whereby attempting to decompress a JPEG file with a corrupt
 header using the `tjDecompressToYUV2()` function would cause the function to

rdppm.c

@@ -5,7 +5,7 @@
  * Copyright (C) 1991-1997, Thomas G. Lane.
  * Modified 2009 by Bill Allombert, Guido Vollbeding.
  * libjpeg-turbo Modifications:
- * Copyright (C) 2015-2017, D. R. Commander.
+ * Copyright (C) 2015-2017, 2020, D. R. Commander.
  * For conditions of distribution and use, see the accompanying README.ijg
  * file.
  *
@@ -720,7 +720,7 @@ start_input_ppm(j_compress_ptr cinfo, cjpeg_source_ptr sinfo)
     /* On 16-bit-int machines we have to be careful of maxval = 65535 */
     source->rescale = (JSAMPLE *)
       (*cinfo->mem->alloc_small) ((j_common_ptr)cinfo, JPOOL_IMAGE,
-                                  (size_t)(((long)maxval + 1L) *
+                                  (size_t)(((long)MAX(maxval, 255) + 1L) *
                                            sizeof(JSAMPLE)));
     half_maxval = maxval / 2;
     for (val = 0; val <= (long)maxval; val++) {