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SubjectRe: [PATCH 3/6] macvtap: zerocopy: validate vector length before pinning user pages
On Mon, Apr 16, 2012 at 02:08:07PM +0800, Jason Wang wrote:
> Currently we do not validate the vector length before calling
> get_user_pages_fast(), host stack would be easily overflowed by
> malicious guest driver who give us a descriptor with length greater
> than MAX_SKB_FRAGS. Solve this problem by checking the free entries
> before trying to pin user pages.
>
> Signed-off-by: Jason Wang <jasowang@redhat.com>

We could handle this by copying and linearising some fragments.
That would be better.

> ---
> drivers/net/macvtap.c | 2 ++
> 1 files changed, 2 insertions(+), 0 deletions(-)
>
> diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c
> index 7cb2684..d197a78 100644
> --- a/drivers/net/macvtap.c
> +++ b/drivers/net/macvtap.c
> @@ -529,6 +529,8 @@ static int zerocopy_sg_from_iovec(struct sk_buff *skb, const struct iovec *from,
> }
> base = (unsigned long)from->iov_base + offset;
> size = ((base & ~PAGE_MASK) + len + ~PAGE_MASK) >> PAGE_SHIFT;
> + if (i + size >= MAX_SKB_FRAGS)
> + return -EFAULT;
> num_pages = get_user_pages_fast(base, size, 0, &page[i]);
> if ((num_pages != size) ||
> (num_pages > MAX_SKB_FRAGS - skb_shinfo(skb)->nr_frags))


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