From de5385cd882a5ff0970f63f4d93da0cbc87230c2 Mon Sep 17 00:00:00 2001

From: =?UTF-8?q?Nikola=20Forr=C3=B3?= <nforro@redhat.com>

Date: Tue, 17 Apr 2018 18:42:09 +0200

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 5e62e81..80aaf8d 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 );

@@ -3506,6 +3507,35 @@ 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 24d4b98..10a588e 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);

-- 

2.17.0