netdev - Re: [PATCH bpf-next] bpf: don't check against device MTU in __bpf_skb_max

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Date:   Mon, 7 Sep 2020 16:07:57 +0200
From:   Jesper Dangaard Brouer <brouer@...hat.com>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     bpf@...r.kernel.org, netdev@...r.kernel.org,
        Daniel Borkmann <borkmann@...earbox.net>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        John Fastabend <john.fastabend@...il.com>, brouer@...hat.com,
        Maciej Zenczykowski <maze@...gle.com>
Subject: Re: [PATCH bpf-next] bpf: don't check against device MTU in
 __bpf_skb_max_len

On Fri, 4 Sep 2020 16:39:47 -0700
Jakub Kicinski <kuba@...nel.org> wrote:

> On Fri, 04 Sep 2020 11:30:28 +0200 Jesper Dangaard Brouer wrote:
> > @@ -3211,8 +3211,7 @@ static int bpf_skb_net_shrink(struct sk_buff *skb, u32 off, u32 len_diff,
> >  
> >  static u32 __bpf_skb_max_len(const struct sk_buff *skb)
> >  {
> > -	return skb->dev ? skb->dev->mtu + skb->dev->hard_header_len :
> > -			  SKB_MAX_ALLOC;
> > +	return SKB_MAX_ALLOC;
> >  }
> >  
> >  BPF_CALL_4(bpf_skb_adjust_room, struct sk_buff *, skb, s32, len_diff,
> >   
> 
> Looks familiar:
> https://lore.kernel.org/netdev/20200420231427.63894-1-zenczykowski@gmail.com/
> 

Great to see that others have proposed same fix before.  Unfortunately
it seems that the thread have died, and no patch got applied to
address this.  (Cc. Maze since he was "mull this over a bit more"...)

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer