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libtiff/SOURCES/0019-CVE-2023-40090-Improved-IFD-Loop-Handling-fixes-455.patch

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From 98648d3b62d4f123915410b8cae47954f9223000 Mon Sep 17 00:00:00 2001
From: Even Rouault <even.rouault@spatialys.com>
Date: Thu, 6 Oct 2022 10:11:06 +0000
Subject: [PATCH] (CVE-2023-40090) Improved IFD-Loop Handling (fixes #455)
Closes #455
See merge request libtiff/libtiff!386
(cherry picked from commit d093eb5d961e21ba51420bc22382c514683a4d91)
---
libtiff/tif_close.c | 6 +-
libtiff/tif_dir.c | 129 +++++++++++++++++++++++++-----------
libtiff/tif_dir.h | 2 +
libtiff/tif_dirread.c | 147 +++++++++++++++++++++++++++++++++---------
libtiff/tif_open.c | 3 +-
libtiff/tiffiop.h | 3 +-
6 files changed, 219 insertions(+), 71 deletions(-)
diff --git a/libtiff/tif_close.c b/libtiff/tif_close.c
index 6c9f7349..b5fa9603 100644
--- a/libtiff/tif_close.c
+++ b/libtiff/tif_close.c
@@ -52,8 +52,10 @@ TIFFCleanup(TIFF* tif)
(*tif->tif_cleanup)(tif);
TIFFFreeDirectory(tif);
- if (tif->tif_dirlist)
- _TIFFfree(tif->tif_dirlist);
+ if (tif->tif_dirlistoff)
+ _TIFFfree(tif->tif_dirlistoff);
+ if (tif->tif_dirlistdirn)
+ _TIFFfree(tif->tif_dirlistdirn);
/*
* Clean up client info links.
diff --git a/libtiff/tif_dir.c b/libtiff/tif_dir.c
index a4295dc9..d9022f5b 100644
--- a/libtiff/tif_dir.c
+++ b/libtiff/tif_dir.c
@@ -1521,12 +1521,22 @@ TIFFDefaultDirectory(TIFF* tif)
}
static int
-TIFFAdvanceDirectory(TIFF* tif, uint64_t* nextdir, uint64_t* off)
+TIFFAdvanceDirectory(TIFF* tif, uint64_t* nextdiroff, uint64_t* off, uint16_t* nextdirnum)
{
static const char module[] = "TIFFAdvanceDirectory";
+
+ /* Add this directory to the directory list, if not already in. */
+ if (!_TIFFCheckDirNumberAndOffset(tif, *nextdirnum, *nextdiroff)) {
+ TIFFErrorExt(tif->tif_clientdata, module, "Starting directory %"PRIu16" at offset 0x%"PRIx64" (%"PRIu64") might cause an IFD loop",
+ *nextdirnum, *nextdiroff, *nextdiroff);
+ *nextdiroff = 0;
+ *nextdirnum = 0;
+ return(0);
+ }
+
if (isMapped(tif))
{
- uint64_t poff=*nextdir;
+ uint64_t poff=*nextdiroff;
if (!(tif->tif_flags&TIFF_BIGTIFF))
{
tmsize_t poffa,poffb,poffc,poffd;
@@ -1537,7 +1547,7 @@ TIFFAdvanceDirectory(TIFF* tif, uint64_t* nextdir, uint64_t* off)
if (((uint64_t)poffa != poff) || (poffb < poffa) || (poffb < (tmsize_t)sizeof(uint16_t)) || (poffb > tif->tif_size))
{
TIFFErrorExt(tif->tif_clientdata,module,"Error fetching directory count");
- *nextdir=0;
+ *nextdiroff=0;
return(0);
}
_TIFFmemcpy(&dircount,tif->tif_base+poffa,sizeof(uint16_t));
@@ -1555,7 +1565,7 @@ TIFFAdvanceDirectory(TIFF* tif, uint64_t* nextdir, uint64_t* off)
_TIFFmemcpy(&nextdir32,tif->tif_base+poffc,sizeof(uint32_t));
if (tif->tif_flags&TIFF_SWAB)
TIFFSwabLong(&nextdir32);
- *nextdir=nextdir32;
+ *nextdiroff=nextdir32;
}
else
{
@@ -1587,11 +1597,10 @@ TIFFAdvanceDirectory(TIFF* tif, uint64_t* nextdir, uint64_t* off)
}
if (off!=NULL)
*off=(uint64_t)poffc;
- _TIFFmemcpy(nextdir,tif->tif_base+poffc,sizeof(uint64_t));
+ _TIFFmemcpy(nextdiroff,tif->tif_base+poffc,sizeof(uint64_t));
if (tif->tif_flags&TIFF_SWAB)
- TIFFSwabLong8(nextdir);
+ TIFFSwabLong8(nextdiroff);
}
- return(1);
}
else
{
@@ -1599,7 +1608,7 @@ TIFFAdvanceDirectory(TIFF* tif, uint64_t* nextdir, uint64_t* off)
{
uint16_t dircount;
uint32_t nextdir32;
- if (!SeekOK(tif, *nextdir) ||
+ if (!SeekOK(tif, *nextdiroff) ||
!ReadOK(tif, &dircount, sizeof (uint16_t))) {
TIFFErrorExt(tif->tif_clientdata, module, "%s: Error fetching directory count",
tif->tif_name);
@@ -1620,13 +1629,13 @@ TIFFAdvanceDirectory(TIFF* tif, uint64_t* nextdir, uint64_t* off)
}
if (tif->tif_flags & TIFF_SWAB)
TIFFSwabLong(&nextdir32);
- *nextdir=nextdir32;
+ *nextdiroff=nextdir32;
}
else
{
uint64_t dircount64;
uint16_t dircount16;
- if (!SeekOK(tif, *nextdir) ||
+ if (!SeekOK(tif, *nextdiroff) ||
!ReadOK(tif, &dircount64, sizeof (uint64_t))) {
TIFFErrorExt(tif->tif_clientdata, module, "%s: Error fetching directory count",
tif->tif_name);
@@ -1646,17 +1655,27 @@ TIFFAdvanceDirectory(TIFF* tif, uint64_t* nextdir, uint64_t* off)
else
(void) TIFFSeekFile(tif,
dircount16*20, SEEK_CUR);
- if (!ReadOK(tif, nextdir, sizeof (uint64_t))) {
+ if (!ReadOK(tif, nextdiroff, sizeof (uint64_t))) {
TIFFErrorExt(tif->tif_clientdata, module,
"%s: Error fetching directory link",
tif->tif_name);
return (0);
}
if (tif->tif_flags & TIFF_SWAB)
- TIFFSwabLong8(nextdir);
+ TIFFSwabLong8(nextdiroff);
}
- return (1);
}
+ if (*nextdiroff != 0) {
+ (*nextdirnum)++;
+ /* Check next directory for IFD looping and if so, set it as last directory. */
+ if (!_TIFFCheckDirNumberAndOffset(tif, *nextdirnum, *nextdiroff)) {
+ TIFFWarningExt(tif->tif_clientdata, module, "the next directory %"PRIu16" at offset 0x%"PRIx64" (%"PRIu64") might be an IFD loop. Treating directory %"PRIu16" as last directory",
+ *nextdirnum, *nextdiroff, *nextdiroff, *nextdirnum-1);
+ *nextdiroff = 0;
+ (*nextdirnum)--;
+ }
+ }
+ return (1);
}
/*
@@ -1666,14 +1685,16 @@ uint16_t
TIFFNumberOfDirectories(TIFF* tif)
{
static const char module[] = "TIFFNumberOfDirectories";
- uint64_t nextdir;
+ uint64_t nextdiroff;
+ uint16_t nextdirnum;
uint16_t n;
if (!(tif->tif_flags&TIFF_BIGTIFF))
- nextdir = tif->tif_header.classic.tiff_diroff;
+ nextdiroff = tif->tif_header.classic.tiff_diroff;
else
- nextdir = tif->tif_header.big.tiff_diroff;
+ nextdiroff = tif->tif_header.big.tiff_diroff;
+ nextdirnum = 0;
n = 0;
- while (nextdir != 0 && TIFFAdvanceDirectory(tif, &nextdir, NULL))
+ while (nextdiroff != 0 && TIFFAdvanceDirectory(tif, &nextdiroff, NULL, &nextdirnum))
{
if (n != 65535) {
++n;
@@ -1696,28 +1717,30 @@ TIFFNumberOfDirectories(TIFF* tif)
int
TIFFSetDirectory(TIFF* tif, uint16_t dirn)
{
- uint64_t nextdir;
+ uint64_t nextdiroff;
+ uint16_t nextdirnum;
uint16_t n;
if (!(tif->tif_flags&TIFF_BIGTIFF))
- nextdir = tif->tif_header.classic.tiff_diroff;
+ nextdiroff = tif->tif_header.classic.tiff_diroff;
else
- nextdir = tif->tif_header.big.tiff_diroff;
- for (n = dirn; n > 0 && nextdir != 0; n--)
- if (!TIFFAdvanceDirectory(tif, &nextdir, NULL))
+ nextdiroff = tif->tif_header.big.tiff_diroff;
+ nextdirnum = 0;
+ for (n = dirn; n > 0 && nextdiroff != 0; n--)
+ if (!TIFFAdvanceDirectory(tif, &nextdiroff, NULL, &nextdirnum))
return (0);
- tif->tif_nextdiroff = nextdir;
+ /* If the n-th directory could not be reached (does not exist),
+ * return here without touching anything further. */
+ if (nextdiroff == 0 || n > 0)
+ return (0);
+
+ tif->tif_nextdiroff = nextdiroff;
/*
* Set curdir to the actual directory index. The
* -1 is because TIFFReadDirectory will increment
* tif_curdir after successfully reading the directory.
*/
tif->tif_curdir = (dirn - n) - 1;
- /*
- * Reset tif_dirnumber counter and start new list of seen directories.
- * We need this to prevent IFD loops.
- */
- tif->tif_dirnumber = 0;
return (TIFFReadDirectory(tif));
}
@@ -1730,13 +1753,42 @@ TIFFSetDirectory(TIFF* tif, uint16_t dirn)
int
TIFFSetSubDirectory(TIFF* tif, uint64_t diroff)
{
- tif->tif_nextdiroff = diroff;
- /*
- * Reset tif_dirnumber counter and start new list of seen directories.
- * We need this to prevent IFD loops.
+ /* Match nextdiroff and curdir for consistent IFD-loop checking.
+ * Only with TIFFSetSubDirectory() the IFD list can be corrupted with invalid offsets
+ * within the main IFD tree.
+ * In the case of several subIFDs of a main image,
+ * there are two possibilities that are not even mutually exclusive.
+ * a.) The subIFD tag contains an array with all offsets of the subIFDs.
+ * b.) The SubIFDs are concatenated with their NextIFD parameters.
+ * (refer to https://www.awaresystems.be/imaging/tiff/specification/TIFFPM6.pdf.)
*/
- tif->tif_dirnumber = 0;
- return (TIFFReadDirectory(tif));
+ int retval;
+ uint16_t curdir = 0;
+ int8_t probablySubIFD = 0;
+ if (diroff == 0) {
+ /* Special case to invalidate the tif_lastdiroff member. */
+ tif->tif_curdir = 65535;
+ } else {
+ if (!_TIFFGetDirNumberFromOffset(tif, diroff, &curdir)) {
+ /* Non-existing offsets might point to a SubIFD or invalid IFD.*/
+ probablySubIFD = 1;
+ }
+ /* -1 because TIFFReadDirectory() will increment tif_curdir. */
+ tif->tif_curdir = curdir - 1;
+ }
+
+ tif->tif_nextdiroff = diroff;
+ retval = TIFFReadDirectory(tif);
+ /* If failed, curdir was not incremented in TIFFReadDirectory(), so set it back. */
+ if (!retval )tif->tif_curdir++;
+ if (retval && probablySubIFD) {
+ /* Reset IFD list to start new one for SubIFD chain and also start SubIFD chain with tif_curdir=0. */
+ tif->tif_dirnumber = 0;
+ tif->tif_curdir = 0; /* first directory of new chain */
+ /* add this offset to new IFD list */
+ _TIFFCheckDirNumberAndOffset(tif, tif->tif_curdir, diroff);
+ }
+ return (retval);
}
/*
@@ -1760,12 +1812,15 @@ TIFFLastDirectory(TIFF* tif)
/*
* Unlink the specified directory from the directory chain.
+ * Note: First directory starts with number dirn=1.
+ * This is different to TIFFSetDirectory() where the first directory starts with zero.
*/
int
TIFFUnlinkDirectory(TIFF* tif, uint16_t dirn)
{
static const char module[] = "TIFFUnlinkDirectory";
uint64_t nextdir;
+ uint16_t nextdirnum;
uint64_t off;
uint16_t n;
@@ -1789,19 +1844,21 @@ TIFFUnlinkDirectory(TIFF* tif, uint16_t dirn)
nextdir = tif->tif_header.big.tiff_diroff;
off = 8;
}
+ nextdirnum = 0; /* First directory is dirn=0 */
+
for (n = dirn-1; n > 0; n--) {
if (nextdir == 0) {
TIFFErrorExt(tif->tif_clientdata, module, "Directory %"PRIu16" does not exist", dirn);
return (0);
}
- if (!TIFFAdvanceDirectory(tif, &nextdir, &off))
+ if (!TIFFAdvanceDirectory(tif, &nextdir, &off, &nextdirnum))
return (0);
}
/*
* Advance to the directory to be unlinked and fetch
* the offset of the directory that follows.
*/
- if (!TIFFAdvanceDirectory(tif, &nextdir, NULL))
+ if (!TIFFAdvanceDirectory(tif, &nextdir, NULL, &nextdirnum))
return (0);
/*
* Go back and patch the link field of the preceding
diff --git a/libtiff/tif_dir.h b/libtiff/tif_dir.h
index 0c251c9e..deaa4594 100644
--- a/libtiff/tif_dir.h
+++ b/libtiff/tif_dir.h
@@ -302,6 +302,8 @@ extern int _TIFFMergeFields(TIFF*, const TIFFField[], uint32_t);
extern const TIFFField* _TIFFFindOrRegisterField(TIFF *, uint32_t, TIFFDataType);
extern TIFFField* _TIFFCreateAnonField(TIFF *, uint32_t, TIFFDataType);
extern int _TIFFCheckFieldIsValidForCodec(TIFF *tif, ttag_t tag);
+extern int _TIFFCheckDirNumberAndOffset(TIFF *tif, uint16_t dirn, uint64_t diroff);
+extern int _TIFFGetDirNumberFromOffset(TIFF *tif, uint64_t diroff, uint16_t *dirn);
#if defined(__cplusplus)
}
diff --git a/libtiff/tif_dirread.c b/libtiff/tif_dirread.c
index 32653f04..f4c1b08d 100644
--- a/libtiff/tif_dirread.c
+++ b/libtiff/tif_dirread.c
@@ -159,7 +159,6 @@ static void TIFFReadDirectoryFindFieldInfo(TIFF* tif, uint16_t tagid, uint32_t*
static int EstimateStripByteCounts(TIFF* tif, TIFFDirEntry* dir, uint16_t dircount);
static void MissingRequired(TIFF*, const char*);
-static int TIFFCheckDirOffset(TIFF* tif, uint64_t diroff);
static int CheckDirCount(TIFF*, TIFFDirEntry*, uint32_t);
static uint16_t TIFFFetchDirectory(TIFF* tif, uint64_t diroff, TIFFDirEntry** pdir, uint64_t* nextdiroff);
static int TIFFFetchNormalTag(TIFF*, TIFFDirEntry*, int recover);
@@ -3922,12 +3921,19 @@ TIFFReadDirectory(TIFF* tif)
int bitspersample_read = FALSE;
int color_channels;
- tif->tif_diroff=tif->tif_nextdiroff;
- if (!TIFFCheckDirOffset(tif,tif->tif_nextdiroff))
- return 0; /* last offset or bad offset (IFD looping) */
- (*tif->tif_cleanup)(tif); /* cleanup any previous compression state */
- tif->tif_curdir++;
- nextdiroff = tif->tif_nextdiroff;
+ if (tif->tif_nextdiroff == 0) {
+ /* In this special case, tif_diroff needs also to be set to 0. */
+ tif->tif_diroff = tif->tif_nextdiroff;
+ return 0; /* last offset, thus no checking necessary */
+ }
+
+ nextdiroff = tif->tif_nextdiroff;
+ /* tif_curdir++ and tif_nextdiroff should only be updated after SUCCESSFUL reading of the directory. Otherwise, invalid IFD offsets could corrupt the IFD list. */
+ if (!_TIFFCheckDirNumberAndOffset(tif, tif->tif_curdir + 1, nextdiroff)) {
+ TIFFWarningExt(tif->tif_clientdata, module,
+ "Didn't read next directory due to IFD looping at offset 0x%"PRIx64" (%"PRIu64") to offset 0x%"PRIx64" (%"PRIu64")", tif->tif_diroff, tif->tif_diroff, nextdiroff, nextdiroff);
+ return 0; /* bad offset (IFD looping) */
+ }
dircount=TIFFFetchDirectory(tif,nextdiroff,&dir,&tif->tif_nextdiroff);
if (!dircount)
{
@@ -3935,6 +3941,11 @@ TIFFReadDirectory(TIFF* tif)
"Failed to read directory at offset %" PRIu64, nextdiroff);
return 0;
}
+ /* Set global values after a valid directory has been fetched.
+ * tif_diroff is already set to nextdiroff in TIFFFetchDirectory() in the beginning. */
+ tif->tif_curdir++;
+ (*tif->tif_cleanup)(tif); /* cleanup any previous compression state */
+
TIFFReadDirectoryCheckOrder(tif,dir,dircount);
/*
@@ -5026,53 +5037,127 @@ MissingRequired(TIFF* tif, const char* tagname)
}
/*
- * Check the directory offset against the list of already seen directory
- * offsets. This is a trick to prevent IFD looping. The one can create TIFF
- * file with looped directory pointers. We will maintain a list of already
- * seen directories and check every IFD offset against that list.
+ * Check the directory number and offset against the list of already seen
+ * directory numbers and offsets. This is a trick to prevent IFD looping.
+ * The one can create TIFF file with looped directory pointers. We will
+ * maintain a list of already seen directories and check every IFD offset
+ * and its IFD number against that list. However, the offset of an IFD number
+ * can change - e.g. when writing updates to file.
+ * Returns 1 if all is ok; 0 if last directory or IFD loop is encountered,
+ * or an error has occured.
*/
-static int
-TIFFCheckDirOffset(TIFF* tif, uint64_t diroff)
+int
+_TIFFCheckDirNumberAndOffset(TIFF *tif, uint16_t dirn, uint64_t diroff)
{
uint16_t n;
if (diroff == 0) /* no more directories */
return 0;
if (tif->tif_dirnumber == 65535) {
- TIFFErrorExt(tif->tif_clientdata, "TIFFCheckDirOffset",
- "Cannot handle more than 65535 TIFF directories");
- return 0;
+ TIFFErrorExt(tif->tif_clientdata, "_TIFFCheckDirNumberAndOffset",
+ "Cannot handle more than 65535 TIFF directories");
+ return 0;
}
- for (n = 0; n < tif->tif_dirnumber && tif->tif_dirlist; n++) {
- if (tif->tif_dirlist[n] == diroff)
- return 0;
+ /* Check if offset is already in the list:
+ * - yes: check, if offset is at the same IFD number - if not, it is an IFD loop
+ * - no: add to list or update offset at that IFD number
+ */
+ for (n = 0; n < tif->tif_dirnumber && tif->tif_dirlistdirn && tif->tif_dirlistoff; n++) {
+ if (tif->tif_dirlistoff[n] == diroff) {
+ if (tif->tif_dirlistdirn[n] == dirn) {
+ return 1;
+ } else {
+ TIFFWarningExt(tif->tif_clientdata, "_TIFFCheckDirNumberAndOffset",
+ "TIFF directory %"PRIu16" has IFD looping to directory %"PRIu16" at offset 0x%"PRIx64" (%"PRIu64")",
+ dirn-1, tif->tif_dirlistdirn[n], diroff, diroff);
+ return 0;
+ }
+ }
+ }
+ /* Check if offset of an IFD has been changed and update offset of that IFD number. */
+ if (dirn < tif->tif_dirnumber && tif->tif_dirlistdirn && tif->tif_dirlistoff) {
+ /* tif_dirlistdirn can have IFD numbers dirn in random order */
+ for (n = 0; n < tif->tif_dirnumber; n++) {
+ if (tif->tif_dirlistdirn[n] == dirn) {
+ tif->tif_dirlistoff[n] = diroff;
+ return 1;
+ }
+ }
}
+ /* Add IFD offset and dirn to IFD directory list */
tif->tif_dirnumber++;
- if (tif->tif_dirlist == NULL || tif->tif_dirnumber > tif->tif_dirlistsize) {
- uint64_t* new_dirlist;
-
+ if (tif->tif_dirlistoff == NULL || tif->tif_dirlistdirn == NULL || tif->tif_dirnumber > tif->tif_dirlistsize) {
+ uint64_t *new_dirlist;
/*
* XXX: Reduce memory allocation granularity of the dirlist
* array.
*/
- new_dirlist = (uint64_t*)_TIFFCheckRealloc(tif, tif->tif_dirlist,
- tif->tif_dirnumber, 2 * sizeof(uint64_t), "for IFD list");
+ if (tif->tif_dirnumber >= 32768)
+ tif->tif_dirlistsize = 65535;
+ else
+ tif->tif_dirlistsize = 2 * tif->tif_dirnumber;
+
+ new_dirlist = (uint64_t *)_TIFFCheckRealloc(tif, tif->tif_dirlistoff,
+ tif->tif_dirlistsize, sizeof(uint64_t), "for IFD offset list");
if (!new_dirlist)
return 0;
- if( tif->tif_dirnumber >= 32768 )
- tif->tif_dirlistsize = 65535;
- else
- tif->tif_dirlistsize = 2 * tif->tif_dirnumber;
- tif->tif_dirlist = new_dirlist;
+ tif->tif_dirlistoff = new_dirlist;
+ new_dirlist = (uint64_t *)_TIFFCheckRealloc(tif, tif->tif_dirlistdirn,
+ tif->tif_dirlistsize, sizeof(uint16_t), "for IFD dirnumber list");
+ if (!new_dirlist)
+ return 0;
+ tif->tif_dirlistdirn = (uint16_t *)new_dirlist;
}
- tif->tif_dirlist[tif->tif_dirnumber - 1] = diroff;
+ tif->tif_dirlistoff[tif->tif_dirnumber - 1] = diroff;
+ tif->tif_dirlistdirn[tif->tif_dirnumber - 1] = dirn;
return 1;
-}
+} /* --- _TIFFCheckDirNumberAndOffset() ---*/
+
+/*
+ * Retrieve the matching IFD directory number of a given IFD offset
+ * from the list of directories already seen.
+ * Returns 1 if the offset was in the list and the directory number
+ * can be returned.
+ * Otherwise returns 0 or if an error occured.
+ */
+int
+_TIFFGetDirNumberFromOffset(TIFF *tif, uint64_t diroff, uint16_t* dirn)
+{
+ uint16_t n;
+
+ if (diroff == 0) /* no more directories */
+ return 0;
+ if (tif->tif_dirnumber == 65535) {
+ TIFFErrorExt(tif->tif_clientdata, "_TIFFGetDirNumberFromOffset",
+ "Cannot handle more than 65535 TIFF directories");
+ return 0;
+ }
+
+ /* Check if offset is already in the list and return matching directory number.
+ * Otherwise update IFD list using TIFFNumberOfDirectories()
+ * and search again in IFD list.
+ */
+ for (n = 0; n < tif->tif_dirnumber && tif->tif_dirlistoff && tif->tif_dirlistdirn; n++) {
+ if (tif->tif_dirlistoff[n] == diroff) {
+ *dirn = tif->tif_dirlistdirn[n];
+ return 1;
+ }
+ }
+ TIFFNumberOfDirectories(tif);
+ for (n = 0; n < tif->tif_dirnumber && tif->tif_dirlistoff && tif->tif_dirlistdirn; n++) {
+ if (tif->tif_dirlistoff[n] == diroff) {
+ *dirn = tif->tif_dirlistdirn[n];
+ return 1;
+ }
+ }
+ return 0;
+} /*--- _TIFFGetDirNumberFromOffset() ---*/
+
/*
* Check the count field of a directory entry against a known value. The
diff --git a/libtiff/tif_open.c b/libtiff/tif_open.c
index 549f56ce..85c2af47 100644
--- a/libtiff/tif_open.c
+++ b/libtiff/tif_open.c
@@ -354,7 +354,8 @@ TIFFClientOpen(
goto bad;
tif->tif_diroff = 0;
tif->tif_lastdiroff = 0;
- tif->tif_dirlist = NULL;
+ tif->tif_dirlistoff = NULL;
+ tif->tif_dirlistdirn = NULL;
tif->tif_dirlistsize = 0;
tif->tif_dirnumber = 0;
return (tif);
diff --git a/libtiff/tiffiop.h b/libtiff/tiffiop.h
index 4e8bdac2..8e0e2454 100644
--- a/libtiff/tiffiop.h
+++ b/libtiff/tiffiop.h
@@ -118,7 +118,8 @@ struct tiff {
uint64_t tif_diroff; /* file offset of current directory */
uint64_t tif_nextdiroff; /* file offset of following directory */
uint64_t tif_lastdiroff; /* file offset of last directory written so far */
- uint64_t* tif_dirlist; /* list of offsets to already seen directories to prevent IFD looping */
+ uint64_t* tif_dirlistoff; /* list of offsets to already seen directories to prevent IFD looping */
+ uint16_t* tif_dirlistdirn; /* list of directory numbers to already seen directories to prevent IFD looping */
uint16_t tif_dirlistsize; /* number of entries in offset list */
uint16_t tif_dirnumber; /* number of already seen directories */
TIFFDirectory tif_dir; /* internal rep of current directory */
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