netdev - Re: tc flower IP address keys

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Date:   Thu, 10 Jan 2019 16:31:23 -0800
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Edward Cree <ecree@...arflare.com>
Cc:     Jamal Hadi Salim <jhs@...atatu.com>, Jiri Pirko <jiri@...nulli.us>,
        netdev <netdev@...r.kernel.org>
Subject: Re: tc flower IP address keys

On Thu, Jan 10, 2019 at 5:42 AM Edward Cree <ecree@...arflare.com> wrote:
>
> I think there is a bug in net/sched/cls_flower.c:fl_init_dissector(),
>  where it reads
>
>     FL_KEY_SET_IF_MASKED(mask, keys, cnt,
>                  FLOW_DISSECTOR_KEY_IPV4_ADDRS, ipv4);
>     FL_KEY_SET_IF_MASKED(mask, keys, cnt,
>                  FLOW_DISSECTOR_KEY_IPV6_ADDRS, ipv6);
>
> (and correspondingly further down for enc IP addrs), in that fl_flow_key
>  stores ipv4 and ipv6 in a union, meaning that if a tc flower filter sets,
>  for instance, a destination IPv4 address (and an ethertype of IPv4), the
>  mask for this will also show up in the middle of the source ipv6 address,
>  and lead to the ipv6 key being marked as used.  Thus subsequently a call
>  to dissector_uses_key(..., FLOW_DISSECTOR_KEY_IPV6_ADDRS) will return
>  true.
> While this can be disambiguated by examining key->control.addr_type, this
>  seems like it ought not to be necessary.  I apologise if this has been
>  asked before, but is there a reason why the core code cannot fix this up
>  and prevent drivers from seeing it in their tc offload routines?

I don't follow this question. The code you quoted from
fl_init_dissector() is correct, as it merely stores the offsets of ipv4/ipv6
fields. If somewhere we use it without checking control.addr_type,
then it is a bug there.

I don't see anything particular here, we use IPv4/IPv6 address union
in so many other places in networking, I don't see why this one is so
special to you. :)

Thanks.