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    Subject[PATCH 4.19 005/267] tun: correct header offsets in napi frags mode
    Date
    From: Willem de Bruijn <willemb@google.com>

    [ Upstream commit 96aa1b22bd6bb9fccf62f6261f390ed6f3e7967f ]

    Tun in IFF_NAPI_FRAGS mode calls napi_gro_frags. Unlike netif_rx and
    netif_gro_receive, this expects skb->data to point to the mac layer.

    But skb_probe_transport_header, __skb_get_hash_symmetric, and
    xdp_do_generic in tun_get_user need skb->data to point to the network
    header. Flow dissection also needs skb->protocol set, so
    eth_type_trans has to be called.

    Ensure the link layer header lies in linear as eth_type_trans pulls
    ETH_HLEN. Then take the same code paths for frags as for not frags.
    Push the link layer header back just before calling napi_gro_frags.

    By pulling up to ETH_HLEN from frag0 into linear, this disables the
    frag0 optimization in the special case when IFF_NAPI_FRAGS is used
    with zero length iov[0] (and thus empty skb->linear).

    Fixes: 90e33d459407 ("tun: enable napi_gro_frags() for TUN/TAP driver")
    Signed-off-by: Willem de Bruijn <willemb@google.com>
    Acked-by: Petar Penkov <ppenkov@google.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    drivers/net/tun.c | 12 +++++++++---
    1 file changed, 9 insertions(+), 3 deletions(-)

    --- a/drivers/net/tun.c
    +++ b/drivers/net/tun.c
    @@ -1870,8 +1870,11 @@ drop:
    skb->dev = tun->dev;
    break;
    case IFF_TAP:
    - if (!frags)
    - skb->protocol = eth_type_trans(skb, tun->dev);
    + if (frags && !pskb_may_pull(skb, ETH_HLEN)) {
    + err = -ENOMEM;
    + goto drop;
    + }
    + skb->protocol = eth_type_trans(skb, tun->dev);
    break;
    }

    @@ -1927,8 +1930,11 @@ drop:
    }

    if (frags) {
    + u32 headlen;
    +
    /* Exercise flow dissector code path. */
    - u32 headlen = eth_get_headlen(skb->data, skb_headlen(skb));
    + skb_push(skb, ETH_HLEN);
    + headlen = eth_get_headlen(skb->data, skb_headlen(skb));

    if (unlikely(headlen > skb_headlen(skb))) {
    this_cpu_inc(tun->pcpu_stats->rx_dropped);

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