Re: negative seek offsets in VFS

[Linus Torvalds <torvalds@osdl.org>]

On Thu, 26 May 2005, Al Viro wrote:
> 
> How about
>         if (unlikely((pos < 0) || (loff_t) (pos + count) < 0))
> 		if (!(file->f_mode & FMODE_ANY_OFFSET))
> 			goto Einval;
> 
> instead + adding
> #define FMODE_ANY_OFFSET 16 /* we don't need any offset checks */
> in fs.h + having kmem ->open() set it?
> 
> Linus, it's your code.  Do you have any objections to the above?

No. But if so, the test should be changed: right now it not only detects 
negative offsets, it also detects wrap-around. And I think that 
wrap-around is _always_ wrong.

I don't think there is a "positive loff_t", so I guess the code would have 
to be something like

	/* Wraparound? */
	if ((u64)(pos + count) < count)
		goto Einval;

	if ((loff_t) (pos + count) < 0)
		if (!(file->f_mode & FMODE_ANY_OFFSET))
			goto Einval;

instead.

			Linus