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    Subject[PATCH 3.10 21/70] macvtap: Fix csum_start when VLAN tags are present
    Date
    3.10-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Herbert Xu <herbert@gondor.apana.org.au>

    commit 3ce9b20f1971690b8b3b620e735ec99431573b39 upstream.

    When VLAN is in use in macvtap_put_user, we end up setting
    csum_start to the wrong place. The result is that the whoever
    ends up doing the checksum setting will corrupt the packet instead
    of writing the checksum to the expected location, usually this
    means writing the checksum with an offset of -4.

    This patch fixes this by adjusting csum_start when VLAN tags are
    detected.

    Fixes: f09e2249c4f5 ("macvtap: restore vlan header on user read")
    Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    Signed-off-by: David S. Miller <davem@davemloft.net>

    ---
    drivers/net/macvtap.c | 2 ++
    1 file changed, 2 insertions(+)

    --- a/drivers/net/macvtap.c
    +++ b/drivers/net/macvtap.c
    @@ -625,6 +625,8 @@ static int macvtap_skb_to_vnet_hdr(const
    if (skb->ip_summed == CHECKSUM_PARTIAL) {
    vnet_hdr->flags = VIRTIO_NET_HDR_F_NEEDS_CSUM;
    vnet_hdr->csum_start = skb_checksum_start_offset(skb);
    + if (vlan_tx_tag_present(skb))
    + vnet_hdr->csum_start += VLAN_HLEN;
    vnet_hdr->csum_offset = skb->csum_offset;
    } else if (skb->ip_summed == CHECKSUM_UNNECESSARY) {
    vnet_hdr->flags = VIRTIO_NET_HDR_F_DATA_VALID;



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