netdev - Re: [PATCH v2 2/2] net: avoid infinite loop in mpls_gso_segment when mpls

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Date:   Mon, 08 Mar 2021 17:26:48 +0100
From:   Balazs Nemeth <bnemeth@...hat.com>
To:     David Ahern <dsahern@...il.com>,
        Willem de Bruijn <willemdebruijn.kernel@...il.com>
Cc:     Network Development <netdev@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        David Miller <davem@...emloft.net>,
        virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH v2 2/2] net: avoid infinite loop in mpls_gso_segment
 when mpls_hlen == 0

On Mon, 2021-03-08 at 09:17 -0700, David Ahern wrote:
> On 3/8/21 9:07 AM, Willem de Bruijn wrote:
> > > diff --git a/net/mpls/mpls_gso.c b/net/mpls/mpls_gso.c
> > > index b1690149b6fa..cc1b6457fc93 100644
> > > --- a/net/mpls/mpls_gso.c
> > > +++ b/net/mpls/mpls_gso.c
> > > @@ -27,7 +27,7 @@ static struct sk_buff *mpls_gso_segment(struct
> > > sk_buff *skb,
> > > 
> > >         skb_reset_network_header(skb);
> > >         mpls_hlen = skb_inner_network_header(skb) -
> > > skb_network_header(skb);
> > > -       if (unlikely(!pskb_may_pull(skb, mpls_hlen)))
> > > +       if (unlikely(!mpls_hlen || !pskb_may_pull(skb,
> > > mpls_hlen)))
> > >                 goto out;
> > 
> > Good cathc. Besides length zero, this can be more strict: a label
> > is
> > 4B, so mpls_hlen needs to be >= 4B.
> > 
> > Perhaps even aligned to 4B, too, but not if there may be other
> > encap on top.
> > 
> > Unfortunately there is no struct or type definition that we can use
> > a
> > sizeof instead of open coding the raw constant.
> > 
> 
> MPLS_HLEN can be used here.
> 

What about sizeof(struct mpls_label), like in net/ipv4/tunnel4.c?