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

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Date:   Fri, 29 Jun 2018 12:52:02 -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 Thu, Jun 28, 2018 at 9:59 PM, Roopa Prabhu <roopa@...ulusnetworks.com> wrote:
> 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).

as I write the commit msg for the new incremental patch, it seems
better to merge this one with the new one.

Please ignore this patch, I will send an updated patch in a bit. thanks.