2017.08.03 15:23 "Re: [Tiff] Error handling in Read/Write/Seek", by Bob Friesenhahn
It seems best to block any negative size values from being passed into these functions in the first place. Libtiff is not in control of the I/O functions, so it is best to assure that they are not passed illegal values which might cause I/O implementations to do very bad things.
Not sure to understand what you mean here. Here are all call locations for SeekOK():
tif_dir.c: 2 times
tif_read.c: 4 times
tif_write.c: 1 time
tif_dirread.c: 3 times
tif_dirwrite.c: 9 times
Do you suggest to add an extra check for (off<0) before each call? If yes, I can prepare a patch.
Yes, I am suggesting that it is best to avoid passing a wrong request to the I/O functions (which might have been implemented by a library user or are implemented in a C library on any operating system libtiff may be compiled on) rather than dealing with a subsquent possible error return due to the wrong request. This approach assures consistent behavior. It can also produce a better quality (more appropriate) error message for the library user.
Also, is there any chance that TIFFSeekFile() could legitimately be called with off<0 and whence=SEEK_CUR? I mean, is there any reason to seek backward in a TIFF file? Looking at the code, the only calls to TIFFSeekFile(whence=SEEK_CUR) take (dircount*object_size) as an offset and should therefore always be positive, but I am not super-familiar with TIFF format(s).
I don't know what might happen in the future. We only know what libtiff does now. The seek operation used should be apparent at each call point.
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