netdev - Re: [PATCH net-next] net/vxlan: Avoid unaligned access in vxlan_build

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Date:   Tue, 20 Sep 2016 08:31:10 -0700
From:   Tom Herbert <tom@...bertland.com>
To:     Sowmini Varadhan <sowmini.varadhan@...cle.com>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jiri Benc <jbenc@...hat.com>,
        Hannes Frederic Sowa <hannes@...essinduktion.org>,
        Alexander Duyck <aduyck@...antis.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Paolo Abeni <pabeni@...hat.com>
Subject: Re: [PATCH net-next] net/vxlan: Avoid unaligned access in vxlan_build_skb()

On Tue, Sep 20, 2016 at 7:27 AM, Sowmini Varadhan
<sowmini.varadhan@...cle.com> wrote:
> The vxlan header is at offset (14 + 20 + 8) into the packet,
> so the vxh is not aligned in vxlan_build_skb. Use [get/put]_unaligned
> functions to modify flags and vni field in the vxh.
>
I'm wondering if VXLAN is just the tip of the iceberg. Wouldn't this
is also be a problem in GRE and Geneve when they encapsulate Ethernet?
What about the outer IP header, wouldn't that potentially have
unaligned accesses also when creating it?

Tom

> Signed-off-by: Sowmini Varadhan <sowmini.varadhan@...cle.com>
> ---
>  drivers/net/vxlan.c |   10 ++++++----
>  1 files changed, 6 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/net/vxlan.c b/drivers/net/vxlan.c
> index e7d1668..f903fa4 100644
> --- a/drivers/net/vxlan.c
> +++ b/drivers/net/vxlan.c
> @@ -1751,15 +1751,17 @@ static int vxlan_build_skb(struct sk_buff *skb, struct dst_entry *dst,
>                 goto out_free;
>
>         vxh = (struct vxlanhdr *) __skb_push(skb, sizeof(*vxh));
> -       vxh->vx_flags = VXLAN_HF_VNI;
> -       vxh->vx_vni = vxlan_vni_field(vni);
> +       put_unaligned(VXLAN_HF_VNI, &vxh->vx_flags);
> +       put_unaligned(vxlan_vni_field(vni), &vxh->vx_vni);
>
>         if (type & SKB_GSO_TUNNEL_REMCSUM) {
>                 unsigned int start;
> +               __be32 tmpvni = get_unaligned(&vxh->vx_vni);
>
>                 start = skb_checksum_start_offset(skb) - sizeof(struct vxlanhdr);
> -               vxh->vx_vni |= vxlan_compute_rco(start, skb->csum_offset);
> -               vxh->vx_flags |= VXLAN_HF_RCO;
> +               tmpvni |= vxlan_compute_rco(start, skb->csum_offset);
> +               put_unaligned(tmpvni, &vxh->vx_vni);
> +               put_unaligned(VXLAN_HF_VNI | VXLAN_HF_RCO, &vxh->vx_flags);
>
>                 if (!skb_is_gso(skb)) {
>                         skb->ip_summed = CHECKSUM_NONE;
> --
> 1.7.1
>