_TIFFCheckMalloc()/_TIFFCheckRealloc() used a unsafe way to detect overflow
in the multiplication of nmemb and elem_size (which are of type tmsize_t, thus
signed), which was especially easily triggered on 32-bit builds (with recent
enough compilers that assume that signed multiplication cannot overflow, since
this is undefined behaviour by the C standard). The original issue which lead to
this fix was trigged from tif_fax3.c
There were also unsafe (implementation defied), and broken in practice on 64bit
builds, ways of checking that a uint64 fits of a (signed) tmsize_t by doing
(uint64)(tmsize_t)uint64_var != uint64_var comparisons. Those have no known
at that time exploits, but are better to fix in a more bullet-proof way.
Or similarly use of (int64)uint64_var <= 0.
IGNORE placeholder in tif_dirread.c is now replaced by a field dir_ignore in the TIFFDirEntry structure
Currently, in tif_dirread.c a special IGNORE value for the tif tags is defined
in order to flag status preventing already processed tags from further processing.
This irrational behaviour prevents reading of custom tags with id code 0 - like tag GPSVERSIONID from EXIF 2.31 definition.
An additional field 'tdir_ignore' is now added to the TIFFDirEntry structure and code is changed
to allow tags with id code 0 to be read correctly.
This change was already proposed as pending improvement in tif_dirread.c around line 32.
Reference is also made to:
- Discussion in https://gitlab.com/libtiff/libtiff/merge_requests/39
- http://bugzilla.maptools.org/show_bug.cgi?id=2540
Comments and indention adapted.
Preparation to rebase onto master
in configure/CMakeList.txt :
- TIFF_INT8_T/TIFF_UINT8_T is signed/unsigned char
sizeof(char)==1 in C standard
- TIFF_INT16_T/TIFF_UINT16_T is signed/unsigned short
sizeof(short)>=2 in C standard
- TIFF_INT32_T/TIFF_UINT32_T is defined so its sizeof() is 4
- TIFF_INT64_T/TIFF_UINT64_T is defined so its sizeof() is 8
- TIFF_SIZE_T is defined so it has same sizeof() than size_t
- TIFF_SSIZE_T is defined so it has same sizeof() than unsigned char *
Those advanced writing functions must be used in a particular sequence
to make their intended effect. Their aim is to control when/where
the [Strip/Tile][Offsets/ByteCounts] arrays are written into the file.
The purpose of this is to generate 'cloud-optimized geotiff' files where
the first KB of the file only contain the IFD entries without the potentially
large strile arrays. Those are written afterwards.
The typical sequence of calls is:
TIFFOpen()
[ TIFFCreateDirectory(tif) ]
Set fields with calls to TIFFSetField(tif, ...)
TIFFDeferStrileArrayWriting(tif)
TIFFWriteCheck(tif, ...)
TIFFWriteDirectory(tif)
... potentially create other directories and come back to the above directory
TIFFForceStrileArrayWriting(tif): emit the arrays at the end of file
See test/defer_strile_writing.c for a practical example.
Found on GDAL with https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=14894
Disabling the TIFF_DEFERSTRILELOAD bit in ChopupStripArray() was a
bad idea since when using TIFFReadDirectory() to reload the directory again
would lead to a different value of td_rowsperstrip, which could confuse
readers if they relied on the value found initially.
This function replaces the use of TIFFReadEncodedStrip()/TIFFReadEncodedTile()
when the user can provide the buffer for the input data, for example when
he wants to avoid libtiff to read the strile offset/count values from the
[Strip|Tile][Offsets/ByteCounts] array.
