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

["David S. Miller" <davem@redhat.com>]

   From: DervishD <raul@pleyades.net>
   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?