From be4c85b16e8801a16eec25e80eb9f3dd6a96731b Mon Sep 17 00:00:00 2001
From: Hugo Lefeuvre <hle@debian.org>
Date: Sun, 8 Apr 2018 14:07:08 -0400
Subject: [PATCH] Fix NULL pointer dereference in TIFFPrintDirectory

The TIFFPrintDirectory function relies on the following assumptions,
supposed to be guaranteed by the specification:

(a) A Transfer Function field is only present if the TIFF file has
    photometric type < 3.

(b) If SamplesPerPixel > Color Channels, then the ExtraSamples field
    has count SamplesPerPixel - (Color Channels) and contains
    information about supplementary channels.

While respect of (a) and (b) are essential for the well functioning of
TIFFPrintDirectory, no checks are realized neither by the callee nor
by TIFFPrintDirectory itself. Hence, following scenarios might happen
and trigger the NULL pointer dereference:

(1) TIFF File of photometric type 4 or more has illegal Transfer
    Function field.

(2) TIFF File has photometric type 3 or less and defines a
    SamplesPerPixel field such that SamplesPerPixel > Color Channels
    without defining all extra samples in the ExtraSamples fields.

In this patch, we address both issues with respect of the following
principles:

(A) In the case of (1), the defined transfer table should be printed
    safely even if it isn't 'legal'. This allows us to avoid expensive
    checks in TIFFPrintDirectory. Also, it is quite possible that
    an alternative photometric type would be developed (not part of the
    standard) and would allow definition of Transfer Table. We want
    libtiff to be able to handle this scenario out of the box.

(B) In the case of (2), the transfer table should be printed at its
    right size, that is if TIFF file has photometric type Palette
    then the transfer table should have one row and not three, even
    if two extra samples are declared.

In order to fulfill (A) we simply add a new 'i < 3' end condition to
the broken TIFFPrintDirectory loop. This makes sure that in any case
where (b) would be respected but not (a), everything stays fine.

(B) is fulfilled by the loop condition
'i < td->td_samplesperpixel - td->td_extrasamples'. This is enough as
long as (b) is respected.

Naturally, we also make sure (b) is respected. This is done in the
TIFFReadDirectory function by making sure any non-color channel is
counted in ExtraSamples.

This commit addresses CVE-2018-7456.
---
 libtiff/tif_dirread.c | 62 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 libtiff/tif_print.c   |  2 +-
 2 files changed, 63 insertions(+), 1 deletion(-)

diff --git a/libtiff/tif_dirread.c b/libtiff/tif_dirread.c
index 6baa7b3..af5b84a 100644
--- a/libtiff/tif_dirread.c
+++ b/libtiff/tif_dirread.c
@@ -167,6 +167,7 @@ static int TIFFFetchStripThing(TIFF* tif, TIFFDirEntry* dir, uint32 nstrips, uin
 static int TIFFFetchSubjectDistance(TIFF*, TIFFDirEntry*);
 static void ChopUpSingleUncompressedStrip(TIFF*);
 static uint64 TIFFReadUInt64(const uint8 *value);
+static int _TIFFGetMaxColorChannels(uint16 photometric);
 
 static int _TIFFFillStrilesInternal( TIFF *tif, int loadStripByteCount );
 
@@ -3507,6 +3508,35 @@ static void TIFFReadDirEntryOutputErr(TIFF* tif, enum TIFFReadDirEntryErr err, c
 }
 
 /*
+ * Return the maximum number of color channels specified for a given photometric
+ * type. 0 is returned if photometric type isn't supported or no default value
+ * is defined by the specification.
+ */
+static int _TIFFGetMaxColorChannels( uint16 photometric )
+{
+    switch (photometric) {
+	case PHOTOMETRIC_PALETTE:
+	case PHOTOMETRIC_MINISWHITE:
+	case PHOTOMETRIC_MINISBLACK:
+            return 1;
+	case PHOTOMETRIC_YCBCR:
+	case PHOTOMETRIC_RGB:
+	case PHOTOMETRIC_CIELAB:
+            return 3;
+	case PHOTOMETRIC_SEPARATED:
+	case PHOTOMETRIC_MASK:
+            return 4;
+	case PHOTOMETRIC_LOGL:
+	case PHOTOMETRIC_LOGLUV:
+	case PHOTOMETRIC_CFA:
+	case PHOTOMETRIC_ITULAB:
+	case PHOTOMETRIC_ICCLAB:
+	default:
+            return 0;
+    }
+}
+
+/*
  * Read the next TIFF directory from a file and convert it to the internal
  * format. We read directories sequentially.
  */
@@ -3522,6 +3552,7 @@ TIFFReadDirectory(TIFF* tif)
 	uint32 fii=FAILED_FII;
         toff_t nextdiroff;
     int bitspersample_read = FALSE;
+        int color_channels;
 
 	tif->tif_diroff=tif->tif_nextdiroff;
 	if (!TIFFCheckDirOffset(tif,tif->tif_nextdiroff))
@@ -4026,6 +4057,37 @@ TIFFReadDirectory(TIFF* tif)
 			}
 		}
 	}
+
+	/*
+	 * Make sure all non-color channels are extrasamples.
+	 * If it's not the case, define them as such.
+	 */
+        color_channels = _TIFFGetMaxColorChannels(tif->tif_dir.td_photometric);
+        if (color_channels && tif->tif_dir.td_samplesperpixel - tif->tif_dir.td_extrasamples > color_channels) {
+                uint16 old_extrasamples;
+                uint16 *new_sampleinfo;
+
+                TIFFWarningExt(tif->tif_clientdata,module, "Sum of Photometric type-related "
+                    "color channels and ExtraSamples doesn't match SamplesPerPixel. "
+                    "Defining non-color channels as ExtraSamples.");
+
+                old_extrasamples = tif->tif_dir.td_extrasamples;
+                tif->tif_dir.td_extrasamples = (tif->tif_dir.td_samplesperpixel - color_channels);
+
+                // sampleinfo should contain information relative to these new extra samples
+                new_sampleinfo = (uint16*) _TIFFcalloc(tif->tif_dir.td_extrasamples, sizeof(uint16));
+                if (!new_sampleinfo) {
+                    TIFFErrorExt(tif->tif_clientdata, module, "Failed to allocate memory for "
+                                "temporary new sampleinfo array (%d 16 bit elements)",
+                                tif->tif_dir.td_extrasamples);
+                    goto bad;
+                }
+
+                memcpy(new_sampleinfo, tif->tif_dir.td_sampleinfo, old_extrasamples * sizeof(uint16));
+                _TIFFsetShortArray(&tif->tif_dir.td_sampleinfo, new_sampleinfo, tif->tif_dir.td_extrasamples);
+                _TIFFfree(new_sampleinfo);
+        }
+
 	/*
 	 * Verify Palette image has a Colormap.
 	 */
diff --git a/libtiff/tif_print.c b/libtiff/tif_print.c
index 8deceb2..1d86adb 100644
--- a/libtiff/tif_print.c
+++ b/libtiff/tif_print.c
@@ -546,7 +546,7 @@ TIFFPrintDirectory(TIFF* tif, FILE* fd, long flags)
 				uint16 i;
 				fprintf(fd, "    %2ld: %5u",
 				    l, td->td_transferfunction[0][l]);
-				for (i = 1; i < td->td_samplesperpixel; i++)
+				for (i = 1; i < td->td_samplesperpixel - td->td_extrasamples && i < 3; i++)
 					fprintf(fd, " %5u",
 					    td->td_transferfunction[i][l]);
 				fputc('\n', fd);
--
libgit2 0.27.0

