cryptoapi incorrect struct page usage

[Mika Penttilä <mika.penttila@kolumbus.fi>]

It seems that cryptoapi usage wrt mm is not safe. At least both ipsec 
and cryptoloop practise these kinds of things :

example from net/xfrm/xfrm_algo.c

int
skb_to_sgvec(struct sk_buff *skb, struct scatterlist *sg, int offset, 
int len)
{
   int start = skb_headlen(skb);
   int i, copy = start - offset;
   int elt = 0;

   if (copy > 0) {
       if (copy > len)
           copy = len;
       sg[elt].page = virt_to_page(skb->data + offset);
       sg[elt].offset = (unsigned long)(skb->data + offset) % PAGE_SIZE;
       sg[elt].length = copy;



so unpinned pages are passed to cryptoapi. Nothing prevents these pages 
from being swapped out. Something like get_user_pages() is needed to pin 
these pages for the duration of crypto operations. Comments?

--Mika


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