netdev - Re: [PATCH bpf] bpf: fix bpf_skb_adjust_net/bpf_skb_proto

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Date:   Sat, 3 Mar 2018 13:08:16 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Daniel Borkmann <daniel@...earbox.net>
Cc:     Daniel Axtens <dja@...ens.net>, ast@...nel.org,
        netdev@...r.kernel.org,
        Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
Subject: Re: [PATCH bpf] bpf: fix bpf_skb_adjust_net/bpf_skb_proto_xlat to
 deal with gso sctp skbs

On Sat, Mar 03, 2018 at 09:57:15PM +0100, Daniel Borkmann wrote:
> On 03/03/2018 05:02 PM, Daniel Axtens wrote:
> >> From: Daniel Axtens <dja@...ens.net>
> >>
> >> SCTP GSO skbs have a gso_size of GSO_BY_FRAGS, so any sort of
> >> unconditionally mangling of that will result in nonsense value
> >> and would corrupt the skb later on.
> >>
> >> Therefore, i) add two helpers skb_increase_gso_size() and
> >> skb_decrease_gso_size() that would throw a one time warning and
> >> bail out for such skbs and ii) refuse and return early with an
> >> error in those BPF helpers that are affected. We do need to bail
> >> out as early as possible from there before any changes on the
> >> skb have been performed.
> >>
> >> Fixes: 6578171a7ff0 ("bpf: add bpf_skb_change_proto helper")
> >> Co-authored-by: Daniel Borkmann <daniel@...earbox.net>
> >> Signed-off-by: Daniel Axtens <dja@...ens.net>
> >> Cc: Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
> >> Acked-by: Alexei Starovoitov <ast@...nel.org>
> > 
> > I've looked over your changes and they all look good to me.
> > 
> >> +/* Note: Should be called only if skb_is_gso(skb) is true */
> >> +static inline bool skb_is_gso_sctp(const struct sk_buff *skb)
> >> +{
> >> +	return skb_shinfo(skb)->gso_type & SKB_GSO_SCTP;
> >> +}
> >> +
> > 
> > This helper is a fantastic idea and I will send a docs update to
> > highlight it.
> 
> Sounds good. There are infact several places in the code that
> could make use of this right away. If you have a chance, this
> could be done in net-next along with the doc update or so.

Applied to bpf tree, Thanks everyone.