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

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Date:   Mon, 8 Mar 2021 09:17:12 -0700
From:   David Ahern <dsahern@...il.com>
To:     Willem de Bruijn <willemdebruijn.kernel@...il.com>,
        Balazs Nemeth <bnemeth@...hat.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 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.