netdev - Re: [PATCH net] bonding: Prevent IPv6 link local address on enslaved devices

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Date:	Fri, 8 Jan 2016 15:34:20 -0500
From:	Karl Heiss <kheiss@...il.com>
To:	Jay Vosburgh <jay.vosburgh@...onical.com>
Cc:	Veaceslav Falico <vfalico@...il.com>,
	Andy Gospodarek <gospo@...ulusnetworks.com>,
	netdev@...r.kernel.org
Subject: Re: [PATCH net] bonding: Prevent IPv6 link local address on enslaved devices

On Fri, Jan 8, 2016 at 2:56 PM, Jay Vosburgh <jay.vosburgh@...onical.com> wrote:
> Karl Heiss <kheiss@...il.com> wrote:
>
>>Upstream commit 1f718f0f4f97 ("bonding: populate neighbour's private on
>>enslave") undoes the fix provided by commit c2edacf80e15 ("bonding / ipv6: no
>>addrconf for slaves separately from master") by effectively setting
>>the slave flag after the slave has been opened.  If the slave comes up quickly
>>enough, it will go through the IPv6 addrconf before the slave flag has been
>>set and will get a link local IPv6 address.
>>
>>Set IFF_SLAVE before dev_open() and clear it after dev_close() to ensure that
>>addrconf knows to ignore on state change.
>
>         I think prepending "During bonding enslavement and removal
> processing," (or the equivalent) makes the above sentence a bit clearer
> as to what's going on.
>

Agreed

>>Fixes: 1f718f0f4f97 ("bonding: populate neighbour's private on enslave")
>>
>>Signed-off-by: Karl Heiss <kheiss@...il.com>
>>---
>> drivers/net/bonding/bond_main.c |    8 ++++++--
>> 1 files changed, 6 insertions(+), 2 deletions(-)
>>
>>diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
>>index 9e0f8a7..200358e 100644
>>--- a/drivers/net/bonding/bond_main.c
>>+++ b/drivers/net/bonding/bond_main.c
>>@@ -1207,7 +1207,6 @@ static int bond_master_upper_dev_link(struct net_device *bond_dev,
>>       err = netdev_master_upper_dev_link_private(slave_dev, bond_dev, slave);
>>       if (err)
>>               return err;
>>-      slave_dev->flags |= IFF_SLAVE;
>>       rtmsg_ifinfo(RTM_NEWLINK, slave_dev, IFF_SLAVE, GFP_KERNEL);
>>       return 0;
>> }
>>@@ -1216,7 +1215,6 @@ static void bond_upper_dev_unlink(struct net_device *bond_dev,
>>                                 struct net_device *slave_dev)
>> {
>>       netdev_upper_dev_unlink(slave_dev, bond_dev);
>>-      slave_dev->flags &= ~IFF_SLAVE;
>>       rtmsg_ifinfo(RTM_NEWLINK, slave_dev, IFF_SLAVE, GFP_KERNEL);
>> }
>
>         Will this change cause issues for user space monitoring of the
> RTM_NEWLINKs, as now the message will have IFF_SLAVE in the flags for
> both the "link" and "unlink" cases?  How would link be distinguished
> from unlink?
>
>         Since the unlink happens only in __bond_release_one or in the
> case of a failure within bond_enslave, does clearing the flag in
> bond_upper_dev_unlink cause any actual issues?
>
>         -J
>

Oops.  You are correct that the RTM_NEWLINK would appear to be identical to
the link case.  I had originally done this to prevent any NETDEV_CHANGE events
from causing the link local address and subsequent neighbor advertisements just
as the device is unlinked.  However, the bond_upper_dev_unlink() changes were a
result of speculation, not actual observation.

If we feel that we are safe from any NETDEV_CHANGE events and/or the
consequences during unlink, I am fine with leaving the bond_upper_dev_unlink()
code as-is.

Karl

(P.S.: Sorry for the resend, Jay)

>>@@ -1465,6 +1463,9 @@ int bond_enslave(struct net_device *bond_dev, struct net_device *slave_dev)
>>               }
>>       }
>>
>>+      /* set slave flag before open to prevent IPv6 addrconf */
>>+      slave_dev->flags |= IFF_SLAVE;
>>+
>>       /* open the slave since the application closed it */
>>       res = dev_open(slave_dev);
>>       if (res) {
>>@@ -1725,6 +1726,7 @@ err_close:
>>       dev_close(slave_dev);
>>
>> err_restore_mac:
>>+      slave_dev->flags &= ~IFF_SLAVE;
>>       if (!bond->params.fail_over_mac ||
>>           BOND_MODE(bond) != BOND_MODE_ACTIVEBACKUP) {
>>               /* XXX TODO - fom follow mode needs to change master's
>>@@ -1906,6 +1908,8 @@ static int __bond_release_one(struct net_device *bond_dev,
>>       /* close slave before restoring its mac address */
>>       dev_close(slave_dev);
>>
>>+      slave_dev->flags &= ~IFF_SLAVE;
>>+
>>       if (bond->params.fail_over_mac != BOND_FOM_ACTIVE ||
>>           BOND_MODE(bond) != BOND_MODE_ACTIVEBACKUP) {
>>               /* restore original ("permanent") mac address */
>>--
>>1.7.1
>>
>
> ---
>         -Jay Vosburgh, jay.vosburgh@...onical.com