Re: [BK-2.4] [PATCH] Small do_mmap_pgoff correction

From: David S. Miller (
Date: Tue Dec 10 2002 - 15:47:40 EST

   From: DervishD <>
   Date: Tue, 10 Dec 2002 21:45:30 +0100

       Hi David :)
> + * NOTE: in this function we rely on TASK_SIZE being lower than
> + * SIZE_MAX-PAGE_SIZE at least. I'm pretty sure that it is.
> This assumption is wrong.
       OK, then another way of fixing the corner case that exists in
   do_mmap_pgoff is needed. You cannot mmap a chunk of memory whose size
   is bigger than SIZE_MAX-PAGE_SIZE, because 'PAGE_ALIGN' will return 0
   when page-aligning the size.
And after your patch, we'd use a zero length. That is a bug.

       Anyway you cannot use a size larger than SIZE_MAX-PAGE_SIZE even
   on sparc64, since mmap will fail when page aligning such a size,
   returning 0 :((( Reverting the change is worse (IMHO).
This is wrong.

I said that the address space can be this huge size. I didn't
say that this means such a huge single mmap() could work.

It makes that your assumption that allows for the code change
you made is invalid.

       if ((len = PAGE_ALIGN(len)) == 0)
       and this returns 0 if the requested size ('len', here) is between
   SIZE_MAX-PAGE_SIZE and SIZE_MAX. And this is wrong.

And your change causes us to use a len of "zero" in this case, how is
that more valid?

Look at what happens, you PAGE_ALIGN(len) after all the range checks
then we use a len of '0' for the rest of the function. How is that
supposed to be better?
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