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From:   Taehee Yoo <ap420073@gmail.com>
Date:   Wed, 23 Oct 2019 01:40:19 +0900
Message-ID: <CAMArcTXhC2O6XiOL0Qm_zRDygeaPuxpz5+jS_s6pVgXQvfaYiA@mail.gmail.com>
Subject: Re: [PATCH net v5 01/10] net: core: limit nested device depth
To:     David Ahern <dsahern@gmail.com>
Cc:     David Miller <davem@davemloft.net>,
        Netdev <netdev@vger.kernel.org>, linux-wireless@vger.kernel.org,
        Jakub Kicinski <jakub.kicinski@netronome.com>,
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        j.vosburgh@gmail.com, vfalico@gmail.com,
        Andy Gospodarek <andy@greyhouse.net>,
        =?UTF-8?B?SmnFmcOtIFDDrXJrbw==?= <jiri@resnulli.us>,
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        Roopa Prabhu <roopa@cumulusnetworks.com>, saeedm@mellanox.com,
        manishc@marvell.com, rahulv@marvell.com, kys@microsoft.com,
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        Stephen Hemminger <stephen@networkplumber.org>,
        sashal@kernel.org, hare@suse.de, varun@chelsio.com,
        ubraun@linux.ibm.com, kgraul@linux.ibm.com,
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        Cody Schuffelen <schuffelen@google.com>, bjorn@mork.no
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On Tue, 22 Oct 2019 at 09:51, David Ahern <dsahern@gmail.com> wrote:
>

Hi David,
Thank you for the review!

> On 10/21/19 12:47 PM, Taehee Yoo wrote:
> > Current code doesn't limit the number of nested devices.
> > Nested devices would be handled recursively and this needs huge stack
> > memory. So, unlimited nested devices could make stack overflow.
> >
> > This patch adds upper_level and lower_level, they are common variables
> > and represent maximum lower/upper depth.
> > When upper/lower device is attached or dettached,
> > {lower/upper}_level are updated. and if maximum depth is bigger than 8,
> > attach routine fails and returns -EMLINK.
> >
> > In addition, this patch converts recursive routine of
> > netdev_walk_all_{lower/upper} to iterator routine.
>
> They were made recursive because of a particular setup. Did you verify
> your changes did not break it? See commits starting with
> 5bb61cb5fd115bed1814f6b97417e0f397da3c79
>

I didn't change the actual logic of walking APIs.
These walking iterator APIs work as DFS.
So it doesn't break existing codes.

> >
> > Test commands:
> >     ip link add dummy0 type dummy
> >     ip link add link dummy0 name vlan1 type vlan id 1
> >     ip link set vlan1 up
> >
> >     for i in {2..55}
> >     do
> >           let A=$i-1
> >
> >           ip link add vlan$i link vlan$A type vlan id $i
> >     done
> >     ip link del dummy0
>
> 8 levels of nested vlan seems like complete nonsense. Why not just limit
> that stacking and not mess with the rest which can affect real use cases?

VLAN, BONDING, TEAM, MACSEC, MACVLAN, IPVLAN, VIRT_WIFI, and VXLAN
These interface types can be nested and these could be combined.

team6
   |
vlan5
   |
team4
    |
macvlan3
    |
bond2
    |
vlan1
    |
dummy0

There are so many similar cases even they are not real use cases.
So I think generic code is needed.

Thank you
Taehee Yoo