1From de5385cd882a5ff0970f63f4d93da0cbc87230c2 Mon Sep 17 00:00:00 2001 2From: =?UTF-8?q?Nikola=20Forr=C3=B3?= <nforro@redhat.com> 3Date: Tue, 17 Apr 2018 18:42:09 +0200 4Subject: [PATCH] Fix NULL pointer dereference in TIFFPrintDirectory 5 6The TIFFPrintDirectory function relies on the following assumptions, 7supposed to be guaranteed by the specification: 8 9(a) A Transfer Function field is only present if the TIFF file has 10 photometric type < 3. 11 12(b) If SamplesPerPixel > Color Channels, then the ExtraSamples field 13 has count SamplesPerPixel - (Color Channels) and contains 14 information about supplementary channels. 15 16While respect of (a) and (b) are essential for the well functioning of 17TIFFPrintDirectory, no checks are realized neither by the callee nor 18by TIFFPrintDirectory itself. Hence, following scenarios might happen 19and trigger the NULL pointer dereference: 20 21(1) TIFF File of photometric type 4 or more has illegal Transfer 22 Function field. 23 24(2) TIFF File has photometric type 3 or less and defines a 25 SamplesPerPixel field such that SamplesPerPixel > Color Channels 26 without defining all extra samples in the ExtraSamples fields. 27 28In this patch, we address both issues with respect of the following 29principles: 30 31(A) In the case of (1), the defined transfer table should be printed 32 safely even if it isn't 'legal'. This allows us to avoid expensive 33 checks in TIFFPrintDirectory. Also, it is quite possible that 34 an alternative photometric type would be developed (not part of the 35 standard) and would allow definition of Transfer Table. We want 36 libtiff to be able to handle this scenario out of the box. 37 38(B) In the case of (2), the transfer table should be printed at its 39 right size, that is if TIFF file has photometric type Palette 40 then the transfer table should have one row and not three, even 41 if two extra samples are declared. 42 43In order to fulfill (A) we simply add a new 'i < 3' end condition to 44the broken TIFFPrintDirectory loop. This makes sure that in any case 45where (b) would be respected but not (a), everything stays fine. 46 47(B) is fulfilled by the loop condition 48'i < td->td_samplesperpixel - td->td_extrasamples'. This is enough as 49long as (b) is respected. 50 51Naturally, we also make sure (b) is respected. This is done in the 52TIFFReadDirectory function by making sure any non-color channel is 53counted in ExtraSamples. 54 55This commit addresses CVE-2018-7456. 56--- 57 libtiff/tif_dirread.c | 62 +++++++++++++++++++++++++++++++++++++++++++ 58 libtiff/tif_print.c | 2 +- 59 2 files changed, 63 insertions(+), 1 deletion(-) 60 61diff --git a/libtiff/tif_dirread.c b/libtiff/tif_dirread.c 62index 5e62e81..80aaf8d 100644 63--- a/libtiff/tif_dirread.c 64+++ b/libtiff/tif_dirread.c 65@@ -167,6 +167,7 @@ static int TIFFFetchStripThing(TIFF* tif, TIFFDirEntry* dir, uint32 nstrips, uin 66 static int TIFFFetchSubjectDistance(TIFF*, TIFFDirEntry*); 67 static void ChopUpSingleUncompressedStrip(TIFF*); 68 static uint64 TIFFReadUInt64(const uint8 *value); 69+static int _TIFFGetMaxColorChannels(uint16 photometric); 70 71 static int _TIFFFillStrilesInternal( TIFF *tif, int loadStripByteCount ); 72 73@@ -3506,6 +3507,35 @@ static void TIFFReadDirEntryOutputErr(TIFF* tif, enum TIFFReadDirEntryErr err, c 74 } 75 } 76 77+/* 78+ * Return the maximum number of color channels specified for a given photometric 79+ * type. 0 is returned if photometric type isn't supported or no default value 80+ * is defined by the specification. 81+ */ 82+static int _TIFFGetMaxColorChannels( uint16 photometric ) 83+{ 84+ switch (photometric) { 85+ case PHOTOMETRIC_PALETTE: 86+ case PHOTOMETRIC_MINISWHITE: 87+ case PHOTOMETRIC_MINISBLACK: 88+ return 1; 89+ case PHOTOMETRIC_YCBCR: 90+ case PHOTOMETRIC_RGB: 91+ case PHOTOMETRIC_CIELAB: 92+ return 3; 93+ case PHOTOMETRIC_SEPARATED: 94+ case PHOTOMETRIC_MASK: 95+ return 4; 96+ case PHOTOMETRIC_LOGL: 97+ case PHOTOMETRIC_LOGLUV: 98+ case PHOTOMETRIC_CFA: 99+ case PHOTOMETRIC_ITULAB: 100+ case PHOTOMETRIC_ICCLAB: 101+ default: 102+ return 0; 103+ } 104+} 105+ 106 /* 107 * Read the next TIFF directory from a file and convert it to the internal 108 * format. We read directories sequentially. 109@@ -3522,6 +3552,7 @@ TIFFReadDirectory(TIFF* tif) 110 uint32 fii=FAILED_FII; 111 toff_t nextdiroff; 112 int bitspersample_read = FALSE; 113+ int color_channels; 114 115 tif->tif_diroff=tif->tif_nextdiroff; 116 if (!TIFFCheckDirOffset(tif,tif->tif_nextdiroff)) 117@@ -4026,6 +4057,37 @@ TIFFReadDirectory(TIFF* tif) 118 } 119 } 120 } 121+ 122+ /* 123+ * Make sure all non-color channels are extrasamples. 124+ * If it's not the case, define them as such. 125+ */ 126+ color_channels = _TIFFGetMaxColorChannels(tif->tif_dir.td_photometric); 127+ if (color_channels && tif->tif_dir.td_samplesperpixel - tif->tif_dir.td_extrasamples > color_channels) { 128+ uint16 old_extrasamples; 129+ uint16 *new_sampleinfo; 130+ 131+ TIFFWarningExt(tif->tif_clientdata,module, "Sum of Photometric type-related " 132+ "color channels and ExtraSamples doesn't match SamplesPerPixel. " 133+ "Defining non-color channels as ExtraSamples."); 134+ 135+ old_extrasamples = tif->tif_dir.td_extrasamples; 136+ tif->tif_dir.td_extrasamples = (tif->tif_dir.td_samplesperpixel - color_channels); 137+ 138+ // sampleinfo should contain information relative to these new extra samples 139+ new_sampleinfo = (uint16*) _TIFFcalloc(tif->tif_dir.td_extrasamples, sizeof(uint16)); 140+ if (!new_sampleinfo) { 141+ TIFFErrorExt(tif->tif_clientdata, module, "Failed to allocate memory for " 142+ "temporary new sampleinfo array (%d 16 bit elements)", 143+ tif->tif_dir.td_extrasamples); 144+ goto bad; 145+ } 146+ 147+ memcpy(new_sampleinfo, tif->tif_dir.td_sampleinfo, old_extrasamples * sizeof(uint16)); 148+ _TIFFsetShortArray(&tif->tif_dir.td_sampleinfo, new_sampleinfo, tif->tif_dir.td_extrasamples); 149+ _TIFFfree(new_sampleinfo); 150+ } 151+ 152 /* 153 * Verify Palette image has a Colormap. 154 */ 155diff --git a/libtiff/tif_print.c b/libtiff/tif_print.c 156index 24d4b98..10a588e 100644 157--- a/libtiff/tif_print.c 158+++ b/libtiff/tif_print.c 159@@ -546,7 +546,7 @@ TIFFPrintDirectory(TIFF* tif, FILE* fd, long flags) 160 uint16 i; 161 fprintf(fd, " %2ld: %5u", 162 l, td->td_transferfunction[0][l]); 163- for (i = 1; i < td->td_samplesperpixel; i++) 164+ for (i = 1; i < td->td_samplesperpixel - td->td_extrasamples && i < 3; i++) 165 fprintf(fd, " %5u", 166 td->td_transferfunction[i][l]); 167 fputc('\n', fd); 168-- 1692.17.0 170 171