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Subject: Re: [PATCH v2 2/2] net: avoid infinite loop in mpls_gso_segment when
 mpls_hlen == 0
To:     Balazs Nemeth <bnemeth@redhat.com>,
        Willem de Bruijn <willemdebruijn.kernel@gmail.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 Miller <davem@davemloft.net>,
        virtualization@lists.linux-foundation.org
References: <cover.1615199056.git.bnemeth@redhat.com>
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 <718e4f13-31a8-037c-9725-08ae3cd93ccd@gmail.com>
 <543ebc518aa31f04bb6a85b66f37d984ede4b031.camel@redhat.com>
From:   David Ahern <dsahern@gmail.com>
Message-ID: <f1fc417e-946b-6e92-3650-865834c289f3@gmail.com>
Date:   Mon, 8 Mar 2021 09:42:49 -0700
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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.
>>>
>>> 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?
> 

I was thinking MPLS_HLEN because of its consistent use with skb
manipulations. net/mpls code uses mpls_shim_hdr over mpls_label.

Looks like the MPLS code could use some cleanups to make this consistent.