Re: [CRYPTO] Fix stack overrun in crypt()

["David S. Miller" <davem@xxxxxxxxxx>]

On Thu, 15 Jul 2004 21:48:40 +1000
Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx> wrote:

> PS I think someone should double-check the logic in the scatterwalk
> stuff, especially the whichbuf bits.

The goal of scatterwalk_whichbuf() is to use the temporary buffer
if we are walking over a page boundary.

We can use walk->data, and thus directly the page involved, if
we do not cross such a boundary.  The test is that all of the
following conditions pass:

        1) nbytes is <= walk->len_this_page

           When scatterwalk_start() is invoked, walk->len_this_page
           is set to the minimum of the remaining scatterlist segment
           length and the remaining bytes in that page itself.

        2) walk->data + nbytes does not straddle a PAGE_CACHE_SIZE
           boundary

This looks all fine to me.