Re: [PATCH net] net/sched: act_mpls: ensure LSE is pullable before reading it

[Jakub Kicinski]

On Wed, 18 Nov 2020 17:36:52 +0100 Davide Caratti wrote:
> when 'act_mpls' is used to mangle the LSE, the current value is read from
> the packet with mpls_hdr(): ensure that the label is contained in the skb
> "linear" area.
> 
> Found by code inspection.
> 
> Fixes: 2a2ea50870ba ("net: sched: add mpls manipulation actions to TC")
> Signed-off-by: Davide Caratti <dcara...@redhat.com>
> ---
>  net/sched/act_mpls.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/net/sched/act_mpls.c b/net/sched/act_mpls.c
> index 5c7456e5b5cf..03138ad59e9b 100644
> --- a/net/sched/act_mpls.c
> +++ b/net/sched/act_mpls.c
> @@ -105,6 +105,9 @@ static int tcf_mpls_act(struct sk_buff *skb, const struct 
> tc_action *a,
>                       goto drop;
>               break;
>       case TCA_MPLS_ACT_MODIFY:
> +             if (!pskb_may_pull(skb,
> +                                skb_network_offset(skb) + sizeof(new_lse)))

nit: MPLS_HLEN?

> +                     goto drop;
>               new_lse = tcf_mpls_get_lse(mpls_hdr(skb), p, false);
>               if (skb_mpls_update_lse(skb, new_lse))
>                       goto drop;