netdev - Re: [PATCH net] net: fib_rules: add protocol check in rule

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Message-ID: <CAJieiUhsvn8s_-EFjJREM0dS7Jg=jw_uLLvLWOOkNfBjdkMdsA@mail.gmail.com>
Date:   Thu, 28 Jun 2018 21:59:57 -0700
From:   Roopa Prabhu <roopa@...ulusnetworks.com>
To:     David Miller <davem@...emloft.net>
Cc:     netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH net] net: fib_rules: add protocol check in rule_find

On Wed, Jun 27, 2018 at 6:27 PM, Roopa Prabhu <roopa@...ulusnetworks.com> wrote:
> From: Roopa Prabhu <roopa@...ulusnetworks.com>
>
> After commit f9d4b0c1e969 ("fib_rules: move common handling of newrule
> delrule msgs into fib_nl2rule"), rule_find is strict about checking
> for an existing rule. rule_find must check against all
> user given attributes, else it may match against a subset
> of attributes and return an existing rule.
>
> In the below case, without support for protocol match, rule_find
> will match only against 'table main' and return an existing rule.
>
> $ip -4 rule add table main protocol boot
> RTNETLINK answers: File exists
>
> This patch adds protocol support to rule_find, forcing it to
> check protocol match if given by the user.
>
> Fixes: f9d4b0c1e969 ("fib_rules: move common handling of newrule delrule msgs into fib_nl2rule")
> Signed-off-by: Roopa Prabhu <roopa@...ulusnetworks.com>
> ---
> I spent some time looking at all match keys today and protocol
> was the only missing one (protocol is not in a released kernel yet).
> The only way this could be avoided is to move back to the old loose
> rule_find. I am worried about this new strict checking surprising users,
> but going back to the previous loose checking does not seem right either.
> If there is a reason to believe that users did rely on the previous
> behaviour, I will be happy to revert. Here is another example of old and
> new behaviour.
>
> old rule_find behaviour:
> $ip -4 rule add table main protocol boot
> $ip -4 rule add table main protocol boot
> $ip -4 rule add table main protocol boot
> $ip rule show
> 0:      from all lookup local
> 32763:  from all lookup main  proto boot
> 32764:  from all lookup main  proto boot
> 32765:  from all lookup main  proto boot
> 32766:  from all lookup main
> 32767:  from all lookup default
>
> new rule_find behaviour (after this patch):
> $ip -4 rule add table main protocol boot
> $ip -4 rule add table main protocol boot
> RTNETLINK answers: File exists
>

I found the case where the new rule_find breaks for add.
$ip -4 rule add table main tos 10 fwmark 1
$ip -4 rule add table main tos 10
RTNETLINK answers: File exists

The key masks in the new and old rule need to be compared .
And it cannot be easily compared today without an elaborate if-else block.
Its best to introduce key masks for easier and accurate rule comparison.
But this is best done in net-next. I will submit an incremental patch
tomorrow to
restore previous rule_exists for the add case and the rest should be good.

The current patch in context is needed regardless.

Thanks (and sorry about the iterations).