Messages in this thread | | | Subject | Re: [PATCH 3/6] macvtap: zerocopy: validate vector length before pinning user pages | From | Eric Dumazet <> | Date | Mon, 16 Apr 2012 08:53:03 +0200 |
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On Mon, 2012-04-16 at 14:08 +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> > --- > 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)) >
Hi Jason
Why is -EFAULT the right error code ?
Also, why not removing the "(num_pages > MAX_SKB_FRAGS - skb_shinfo(skb)->nr_frags)" test done few lines after ?
Also, if get_user_pages_fast() returns truncated result (size - 1 for example), we apparently dont free the references on pages.
The comment applies only on pages that were added in skb frags.
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