On Wed, Jul 10, 2013 at 01:43:28PM +0800, Jason Wang wrote:
> Userspace may produce vectors greater than MAX_SKB_FRAGS. When we try to
> linearize parts of the skb to let the rest of iov to be fit in
> the frags, we need count copylen into linear when calling macvtap_alloc_skb()
> instead of partly counting it into data_len. Since this breaks
> zerocopy_sg_from_iovec() since its inner counter assumes nr_frags should
> be zero at beginning. This cause nr_frags to be increased wrongly without
> setting the correct frags.
>
> This bug were introduced from b92946e2919134ebe2a4083e4302236295ea2a73
> (macvtap: zerocopy: validate vectors before building skb).
>
> Cc: Michael S. Tsirkin <m...@redhat.com>
> Signed-off-by: Jason Wang <jasow...@redhat.com>
Acked-by: Michael S. Tsirkin <m...@redhat.com>
> ---
> - This patch is needed for stable.
> - Changes from v1: introduce a local variable to track linear size.
> ---
> drivers/net/macvtap.c | 8 ++++++--
> 1 files changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c
> index b6dd6a7..502d948 100644
> --- a/drivers/net/macvtap.c
> +++ b/drivers/net/macvtap.c
> @@ -647,6 +647,7 @@ static ssize_t macvtap_get_user(struct macvtap_queue *q,
> struct msghdr *m,
> int vnet_hdr_len = 0;
> int copylen = 0;
> bool zerocopy = false;
> + size_t linear;
>
> if (q->flags & IFF_VNET_HDR) {
> vnet_hdr_len = q->vnet_hdr_sz;
> @@ -701,11 +702,14 @@ static ssize_t macvtap_get_user(struct macvtap_queue
> *q, struct msghdr *m,
> copylen = vnet_hdr.hdr_len;
> if (!copylen)
> copylen = GOODCOPY_LEN;
> - } else
> + linear = copylen;
> + } else {
> copylen = len;
> + linear = vnet_hdr.hdr_len;
> + }
>
> skb = macvtap_alloc_skb(&q->sk, NET_IP_ALIGN, copylen,
> - vnet_hdr.hdr_len, noblock, &err);
> + linear, noblock, &err);
> if (!skb)
> goto err;
>
> --
> 1.7.1
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