netdev - Re: llc needs namespace awareness asap, was Re: Patch fixing STP if bridge in non-default namespace.

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Date: Tue, 11 Jul 2023 16:40:03 -0500
From: Harry Coin <hcoin@...etfountain.com>
To: Andrew Lunn <andrew@...n.ch>
Cc: Kuniyuki Iwashima <kuniyu@...zon.com>, netdev@...r.kernel.org
Subject: Re: llc needs namespace awareness asap, was Re: Patch fixing STP if
 bridge in non-default namespace.


On 7/11/23 15:44, Andrew Lunn wrote:
>>>>>> The current llc_rcv.c around line 166 in net/llc/llc_input.c  has
>>>>>>
>>>>>>            if (!net_eq(dev_net(dev), &init_net))
>>>>>>                    goto drop;
>>>>>>
>> Thank you!  When you offer your patches, and you hear worries about being
>> 'invasive', it's worth asking 'compared to what' -- since the 'status quo'
>> is every bridge with STP in a non default namespace with a loop in it
>> somewhere will freeze every connected system more solid than ice in
>> Antarctica.
> https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
>
> say:
>
> o It must be obviously correct and tested.
> o It cannot be bigger than 100 lines, with context.
> o It must fix only one thing.
> o It must fix a real bug that bothers people (not a, "This could be a problem..." type thing).
>
> git blame shows:
>
> commit 721499e8931c5732202481ae24f2dfbf9910f129
> Author: YOSHIFUJI Hideaki <yoshfuji@...ux-ipv6.org>
> Date:   Sat Jul 19 22:34:43 2008 -0700
>
>      netns: Use net_eq() to compare net-namespaces for optimization.
>
> diff --git a/net/llc/llc_input.c b/net/llc/llc_input.c
> index 1c45f172991e..57ad974e4d94 100644
> --- a/net/llc/llc_input.c
> +++ b/net/llc/llc_input.c
> @@ -150,7 +150,7 @@ int llc_rcv(struct sk_buff *skb, struct net_device *dev,
>          int (*rcv)(struct sk_buff *, struct net_device *,
>                     struct packet_type *, struct net_device *);
>   
> -       if (dev_net(dev) != &init_net)
> +       if (!net_eq(dev_net(dev), &init_net))
>                  goto drop;
>   
>          /*
>
> So this is just an optimization.
>
> The test itself was added in
>
> ommit e730c15519d09ea528b4d2f1103681fa5937c0e6
> Author: Eric W. Biederman <ebiederm@...ssion.com>
> Date:   Mon Sep 17 11:53:39 2007 -0700
>
>      [NET]: Make packet reception network namespace safe
>      
>      This patch modifies every packet receive function
>      registered with dev_add_pack() to drop packets if they
>      are not from the initial network namespace.
>      
>      This should ensure that the various network stacks do
>      not receive packets in a anything but the initial network
>      namespace until the code has been converted and is ready
>      for them.
>      
>      Signed-off-by: Eric W. Biederman <ebiederm@...ssion.com>
>      Signed-off-by: David S. Miller <davem@...emloft.net>
>
> So that was over 15 years ago.
>
> It appears it has not bothered people for over 15 years.
>
> Lets wait until we get to see the actual fix. We can then decide how
> simple/hard it is to back port to stable, if it fulfils the stable
> rules or not.
>
>        Andrew

Andrew, fair enough.  In the time until it's fixed, the kernel folks 
should publish an advisory and block any attempt to set bridge stp state 
to other than 0 if in a non-default namespace. The alternative is a 
packet flood at whatever the top line speed is should there be a loop 
somewhere in even one connected link.


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