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From:   Willem de Bruijn <willemdebruijn.kernel@gmail.com>
Date:   Tue, 9 Mar 2021 09:29:31 -0500
Message-ID: <CA+FuTSfd=47GLDui1mmg_+OgG+OYf80XYKqMEvKUhbzJFM=dQw@mail.gmail.com>
Subject: Re: [PATCH net v3 2/2] net: avoid infinite loop in mpls_gso_segment
 when mpls_hlen == 0
To:     Balazs Nemeth <bnemeth@redhat.com>
Cc:     Network Development <netdev@vger.kernel.org>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        "Michael S. Tsirkin" <mst@redhat.com>,
        Jason Wang <jasowang@redhat.com>,
        David Ahern <dsahern@gmail.com>,
        David Miller <davem@davemloft.net>,
        virtualization@lists.linux-foundation.org
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On Tue, Mar 9, 2021 at 6:32 AM Balazs Nemeth <bnemeth@redhat.com> wrote:
>
> A packet with skb_inner_network_header(skb) == skb_network_header(skb)
> and ETH_P_MPLS_UC will prevent mpls_gso_segment from pulling any headers
> from the packet. Subsequently, the call to skb_mac_gso_segment will
> again call mpls_gso_segment with the same packet leading to an infinite
> loop. In addition, ensure that the header length is a multiple of four,
> which should hold irrespective of the number of stacked labels.
>
> Signed-off-by: Balazs Nemeth <bnemeth@redhat.com>

Acked-by: Willem de Bruijn <willemb@google.com>

The compiler will convert that modulo into a cheap & (ETH_HLEN - 1)
test for this constant.