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

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Date:   Mon, 8 Mar 2021 13:11:30 -0500
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     David Ahern <dsahern@...il.com>
Cc:     Balazs Nemeth <bnemeth@...hat.com>,
        Willem de Bruijn <willemdebruijn.kernel@...il.com>,
        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, Mar 8, 2021 at 11:43 AM David Ahern <dsahern@...il.com> wrote:
>
> On 3/8/21 9:26 AM, Balazs Nemeth wrote:
> > 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.

On second thought, since mpls_gso_segment pulls all these headers, it
is correct to require it to be a multiple of MPLS_HLEN.