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April 2009
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2009.04.30 19:25 "Re: Packbits worst case encoded length", by Toby Thain
On 30-Apr-09, at 3:12 PM, Albert Cahalan wrote: > On Thu, Apr 30, 2009 at 9:58 AM, Toby Thain > <toby@telegraphics.com.au> wrote: > >> There must be a lot of code out there that assumes good input. And >> if you're >> writing a quick hack, not a general purpose library, you might >> choose to do > > Sure. This being the tiff mailing list, it's reasonable to assume > that this code is going into something, possibly libtiff itself, > that needs to deal with files from random sources. > >> (Relying on memory protection to save you is not a portable >> strategy, so >> again unsuitable for a general purpose library.) > > You may imagine that you are so much more capable than > the people at Microsoft, Adobe, Apple... and so you NEVER > make a mistake that could result in a buffer overflow... Of course not. > > At the very least, you can have an #ifdef to enable memory > protection on platforms that can support it. Windows and > all the typical UNIX-like systems offer this. They offer it for processes for 'free', as far as an application developer is concerned. Whether libtiff should use such a facility directly? Well, the debate is open, I guess. > > BTW, since infinite portability is far too costly for the value it > provides, you do draw a line somewhere. Crummy platforms > are likely to be writing files only, not reading them. (embedded > OSes in cameras, scanners, etc.) At most they need to read > their own files, which will of course be well-formed. > > Going without the memory protection is really really bad. I don't, and haven't since Mac OS 9. And my Linux and Solaris systems don't do without it either. > I can't possibly emphasize this enough. There is no reason > to believe you are some super programmer who never > makes a bug. I do not believe any such thing. When did you stop beating your wife? --T