netdev - Re: [net-next] bonding: don't allow the master to become its slave

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Date:	Thu, 9 Aug 2012 17:52:57 -0300
From:	Flavio Leitner <fbl@...hat.com>
To:	Jiri Pirko <jpirko@...hat.com>
Cc:	Ben Hutchings <bhutchings@...arflare.com>,
	netdev <netdev@...r.kernel.org>, Jay Vosburgh <fubar@...ibm.com>,
	Andy Gospodarek <andy@...yhouse.net>,
	Leonardo Chiquitto <lchiquitto@...e.com>
Subject: Re: [net-next] bonding: don't allow the master to become its slave

On Thu, 9 Aug 2012 21:55:39 +0200
Jiri Pirko <jpirko@...hat.com> wrote:

> Thu, Aug 09, 2012 at 09:39:06PM CEST, fbl@...hat.com wrote:
> >On Thu, 9 Aug 2012 20:03:23 +0100
> >Ben Hutchings <bhutchings@...arflare.com> wrote:
> >
> >> On Thu, 2012-08-09 at 15:30 -0300, Flavio Leitner wrote:
> >> > It doesn't make any sense to allow the master to become
> >> > its slave. That creates a loop of events causing a crash.
> >> 
> >> What if there are other intermediate devices, e.g. the slave is a VLAN
> >> sub-device of the bond?  And doesn't team also have this problem?
> >> 
> >> I think a more general check for such loops might be required.
> >
> >Maybe patching netdev_set_master() to fail in the loop case is
> >the way to go.  That would work for bonding, team and bridge.
> >
> >What you think?
> 
> How about other devices who do not use "->master" like vlan, macvlan?

Didn't get you. This is what I had in mind, just to show the idea.

diff --git a/net/core/dev.c b/net/core/dev.c
index f91abf8..a404afb 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -4424,6 +4424,24 @@ static int __init dev_proc_init(void)
 #define dev_proc_init() 0
 #endif	/* CONFIG_PROC_FS */
 
+bool netdev_check_loop(struct net_device *master, struct net_device *dev)
+{
+	if (master == dev)
+		return true;
+
+	if (is_vlan_dev(dev))
+		return nedev_check_loop(vlan_dev_real_dev(dev));
+
+	/* is a bridge ?*/
+	if (dev->priv_flags & IFF_EBRIDGE) {
+		list_for_each_entry(p, &br->port_list, list) {
+			if (nedev_check_loop(p->dev))
+				return true;
+		}
+	}
+
+	return false;
+}
 
 /**
  *	netdev_set_master	-	set up master pointer
@@ -4447,6 +4465,9 @@ int netdev_set_master(struct net_device *slave, struct net_device *master)
 		dev_hold(master);
 	}
 
+	if (netdev_check_loop(master, slave))
+		return -EINVAL;
+
 	slave->master = master;
 
 	if (old)


fbl
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