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    Subject[PATCH 4.14 111/496] virtio_net: fix XDP code path in receive_small()
    Date
    4.14-stable review patch.  If anyone has any objections, please let me know.

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

    From: Jesper Dangaard Brouer <brouer@redhat.com>

    [ Upstream commit 95dbe9e7b3720efa5cf83d21f44f6d953f7cf4a2 ]

    When configuring virtio_net to use the code path 'receive_small()',
    in-order to get correct XDP_REDIRECT support, I discovered TCP packets
    would get silently dropped when loading an XDP program action XDP_PASS.

    The bug seems to be that receive_small() when XDP is loaded check that
    hdr->hdr.flags is zero, which seems wrong as hdr.flags contains the
    flags VIRTIO_NET_HDR_F_* :
    #define VIRTIO_NET_HDR_F_NEEDS_CSUM 1 /* Use csum_start, csum_offset */
    #define VIRTIO_NET_HDR_F_DATA_VALID 2 /* Csum is valid */

    TCP got dropped as it had the VIRTIO_NET_HDR_F_DATA_VALID flag set.

    The flags that are relevant here are the VIRTIO_NET_HDR_GSO_* flags
    stored in hdr->hdr.gso_type. Thus, the fix is just check that none of
    the gso_type flags have been set.

    Fixes: bb91accf2733 ("virtio-net: XDP support for small buffers")
    Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
    Acked-by: John Fastabend <john.fastabend@gmail.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    drivers/net/virtio_net.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    --- a/drivers/net/virtio_net.c
    +++ b/drivers/net/virtio_net.c
    @@ -513,7 +513,7 @@ static struct sk_buff *receive_small(str
    void *orig_data;
    u32 act;

    - if (unlikely(hdr->hdr.gso_type || hdr->hdr.flags))
    + if (unlikely(hdr->hdr.gso_type))
    goto err_xdp;

    if (unlikely(xdp_headroom < virtnet_get_headroom(vi))) {

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