On Fri, Sep 29, 2023 at 10:42:10AM +0200, Florian Westphal wrote:
> nft can perform merging of adjacent payload requests.
> This means that:
>
> ether saddr 00:11 ... ether type 8021ad ...
>
> is a single payload expression, for 8 bytes, starting at the
> ethernet source offset.
>
> Check that offset+length is fully within the source/destination mac
> addersses.
>
> This bug prevents 'ether type' from matching the correct h_proto in case
> vlan tag got stripped.
Patch LGTM, thanks for fixing my bug.
> Fixes: de6843be3082 ("netfilter: nft_payload: rebuild vlan header when needed")
> Reported-by: David Ward <david.ward@xxxxxxxxxx>
> Signed-off-by: Florian Westphal <fw@xxxxxxxxx>
> ---
> net/netfilter/nft_payload.c | 13 ++++++++++++-
> 1 file changed, 12 insertions(+), 1 deletion(-)
>
> diff --git a/net/netfilter/nft_payload.c b/net/netfilter/nft_payload.c
> index 8cb800989947..120f6d395b98 100644
> --- a/net/netfilter/nft_payload.c
> +++ b/net/netfilter/nft_payload.c
> @@ -154,6 +154,17 @@ int nft_payload_inner_offset(const struct nft_pktinfo *pkt)
> return pkt->inneroff;
> }
>
> +static bool nft_payload_need_vlan_copy(const struct nft_payload *priv)
> +{
> + unsigned int len = priv->offset + priv->len;
> +
> + /* data past ether src/dst requested, copy needed */
> + if (len > offsetof(struct ethhdr, h_proto))
> + return true;
> +
> + return false;
> +}
> +
> void nft_payload_eval(const struct nft_expr *expr,
> struct nft_regs *regs,
> const struct nft_pktinfo *pkt)
> @@ -172,7 +183,7 @@ void nft_payload_eval(const struct nft_expr *expr,
> goto err;
>
> if (skb_vlan_tag_present(skb) &&
> - priv->offset >= offsetof(struct ethhdr, h_proto)) {
> + nft_payload_need_vlan_copy(priv)) {
> if (!nft_payload_copy_vlan(dest, skb,
> priv->offset, priv->len))
> goto err;
> --
> 2.41.0
>
