Linux Ethernet Bridging - Jul 2023 - [Bridge] llc needs namespace awareness asap, was Re: Patch fixing STP if bridge in non-default namespace.

(CC'ing bridge maintainers.)

Kuniyuki Iwashima <kuniyu at amazon.com> writes:
> From: Harry Coin <hcoin at quietfountain.com>
> Date: Tue, 11 Jul 2023 16:40:03 -0500
>> 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 at linux-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 at xmission.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 at
xmission.com>
>> >      Signed-off-by: David S. Miller <davem at davemloft.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.
>
> Like this ?  Someone who didn't notice the issue might complain about
> it as regression.
>
> ---8<---
> diff --git a/net/bridge/br_stp_if.c b/net/bridge/br_stp_if.c
> index 75204d36d7f9..a807996ac56b 100644
> --- a/net/bridge/br_stp_if.c
> +++ b/net/bridge/br_stp_if.c
> @@ -201,6 +201,11 @@ int br_stp_set_enabled(struct net_bridge *br, unsigned
long val,
>  {
>  	ASSERT_RTNL();
>  
> +	if (!net_eq(dev_net(br->dev), &init_net)) {
> +		NL_SET_ERR_MSG_MOD(extack, "STP can't be enabled in non-root
netns");
> +		return -EINVAL;
> +	}
> +
>  	if (br_mrp_enabled(br)) {
>  		NL_SET_ERR_MSG_MOD(extack,
>  				   "STP can't be enabled if MRP is already enabled");
> ---8<---