Re: [PATCH v2 2/2] net: avoid infinite loop in mpls_gso_segment when mpls_hlen == 0

[David Ahern]

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.