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:

quoted

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.