netdev - Re: [PATCH net v4 2/8] ipv4: Honour NLM_F_MATCH, make semantics of NETLINK_GET_STRICT

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Date:   Fri, 14 Jun 2019 21:13:38 -0600
From:   David Ahern <dsahern@...il.com>
To:     Stefano Brivio <sbrivio@...hat.com>,
        David Miller <davem@...emloft.net>,
        Martin KaFai Lau <kafai@...com>
Cc:     Jianlin Shi <jishi@...hat.com>, Wei Wang <weiwan@...gle.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Matti Vaittinen <matti.vaittinen@...rohmeurope.com>,
        netdev@...r.kernel.org
Subject: Re: [PATCH net v4 2/8] ipv4: Honour NLM_F_MATCH, make semantics of
 NETLINK_GET_STRICT_CHK consistent

On 6/14/19 7:32 PM, Stefano Brivio wrote:
> Socket option NETLINK_GET_STRICT_CHK, quoting from commit 89d35528d17d
> ("netlink: Add new socket option to enable strict checking on dumps"),
> is used to "request strict checking of headers and attributes on dump
> requests".
> 
> If some attributes are set (including flags), setting this option causes
> dump functions to filter results according to these attributes, via the
> filter_set flag. However, if strict checking is requested, this should
> imply that we also filter results based on flags that are *not* set.

I don't agree with that comment. If a request does not specify a bit or
specify an attribute on the request, it is a wildcard in the sense of
nothing to be considered when matching records to be returned.


> 
> This is currently not the case, at least for IPv4 FIB dumps: if the
> RTM_F_CLONED flag is not set, and strict checking is required, we should
> not return routes with the RTM_F_CLONED flag set.

IPv4 currently ignores the CLONED flag and just returns - regardless of
whether strict checking is enabled. This is the original short cut added
many years ago.

> 
> Set the filter_set flag whenever strict checking is requested, limiting
> the scope to IPv4 FIB dumps for the moment being, as other users of the
> flag might not present this inconsistency.
> 
> Note that this partially duplicates the semantics of NLM_F_MATCH as
> described by RFC 3549, par. 3.1.1. Instead of setting a filter based on
> the size of the netlink message, properly support NLM_F_MATCH, by
> setting a filter via ip_filter_fib_dump_req() and setting the filter_set
> flag.
> 

your commit description is very confusing given the end goal. can you
explain again?