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

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Message-ID: <20230711215132.77594-1-kuniyu@amazon.com>
Date: Tue, 11 Jul 2023 14:51:32 -0700
From: Kuniyuki Iwashima <kuniyu@...zon.com>
To: <hcoin@...etfountain.com>
CC: <andrew@...n.ch>, <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.

From: Harry Coin <hcoin@...etfountain.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@...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.

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<---