[PATCH net-next] ipv6: recreate ipv6 link-local addresses when increasing MTU over IPV6_MIN_MTU

Take into consideration that the interface might be disabled for IPv6,
thus switch event type.

Signed-off-by: Hannes Frederic Sowa <redacted>
---
 net/ipv6/addrconf.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index d0c685c..c2dcebe 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c

@@ -3149,6 +3149,7 @@ static int addrconf_notify(struct notifier_block *this, unsigned long event,
 
 	case NETDEV_UP:
 	case NETDEV_CHANGE:
+netdev_change:
 		if (dev->flags & IFF_SLAVE)
 			break;
 

@@ -3244,8 +3245,10 @@ static int addrconf_notify(struct notifier_block *this, unsigned long event,
 
 		if (!idev && dev->mtu >= IPV6_MIN_MTU) {
 			idev = ipv6_add_dev(dev);
-			if (!IS_ERR(idev))
-				break;
+			if (!IS_ERR(idev)) {
+				event = NETDEV_UP;
+				goto netdev_change;
+			}
 		}
 
 		/*

-- 
2.5.0

On 10/26/2015 07:36 AM, Hannes Frederic Sowa wrote:

Seems like this code isn't quite correct.  You are calling ipv6_add_dev 
for slave devices, and if I understand things correctly I don't believe 
that was happening before and may be an unintended side effect.

You might want to instead just make it so that you only do the jump, and 
perhaps change the code in the NETDEV_UP/NETDEV_CHANGE section so that 
you test for NETDEV_CHANGE instead of NETDEV_UP.  That should be enough 
to get the effect you are looking for and I believe there would be no 
change to behaviour other than adding IPv6 link-local addresses when the 
MTU is increased.

Give me a bit and I can submit an alternative that may actually work out 
a bit better I think.

- Alex

Hi Alex,

On Mon, Oct 26, 2015, at 16:52, Alexander Duyck wrote:

On 10/26/2015 07:36 AM, Hannes Frederic Sowa wrote:

quoted

Take into consideration that the interface might be disabled for IPv6,
thus switch event type.

Signed-off-by: Hannes Frederic Sowa <redacted>
---
  net/ipv6/addrconf.c | 7 +++++--
  1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index d0c685c..c2dcebe 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c

@@ -3149,6 +3149,7 @@ static int addrconf_notify(struct notifier_block *this, unsigned long event,
  
  	case NETDEV_UP:
  	case NETDEV_CHANGE:
+netdev_change:
  		if (dev->flags & IFF_SLAVE)
  			break;
  

@@ -3244,8 +3245,10 @@ static int addrconf_notify(struct notifier_block *this, unsigned long event,
  
  		if (!idev && dev->mtu >= IPV6_MIN_MTU) {
  			idev = ipv6_add_dev(dev);
-			if (!IS_ERR(idev))
-				break;
+			if (!IS_ERR(idev)) {
+				event = NETDEV_UP;
+				goto netdev_change;
+			}
  		}
  
  		/*

Seems like this code isn't quite correct.  You are calling ipv6_add_dev 
for slave devices, and if I understand things correctly I don't believe 
that was happening before and may be an unintended side effect.

Hmm, could you quickly help me where I get into this situation? I made
sure I enter the NETDEV_UP part before the IFF_SLAVE test and
disable_ipv6 test.

You might want to instead just make it so that you only do the jump, and 
perhaps change the code in the NETDEV_UP/NETDEV_CHANGE section so that 
you test for NETDEV_CHANGE instead of NETDEV_UP.  That should be enough 
to get the effect you are looking for and I believe there would be no 
change to behaviour other than adding IPv6 link-local addresses when the 
MTU is increased.

Give me a bit and I can submit an alternative that may actually work out 
a bit better I think.

If you go the NETDEV_CHANGE route instead of NETDEV_UP, you end up with
the IF_READY flag already set from ipv6_add_dev and thus won't do any
initialization of the device.

Sure, I wait.

Bye,
Hannes

Hello Alex,

On Mon, Oct 26, 2015, at 16:52, Alexander Duyck wrote:

Seems like this code isn't quite correct.  You are calling ipv6_add_dev 
for slave devices, and if I understand things correctly I don't believe 
that was happening before and may be an unintended side effect.

Ah, btw., autoconf and ipv6 operation on IFF_SLAVE devices is actually
desired nowadays and don't think we can change this. See also:
<https://patchwork.ozlabs.org/patch/531196/>

Bye,
Hannes

On 10/26/2015 09:05 AM, Hannes Frederic Sowa wrote:

Hi Alex,

On Mon, Oct 26, 2015, at 16:52, Alexander Duyck wrote:

quoted

On 10/26/2015 07:36 AM, Hannes Frederic Sowa wrote:

quoted

Take into consideration that the interface might be disabled for IPv6,
thus switch event type.

Signed-off-by: Hannes Frederic Sowa <redacted>
---
   net/ipv6/addrconf.c | 7 +++++--
   1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index d0c685c..c2dcebe 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c

@@ -3149,6 +3149,7 @@ static int addrconf_notify(struct notifier_block *this, unsigned long event,
   
   	case NETDEV_UP:
   	case NETDEV_CHANGE:
+netdev_change:
   		if (dev->flags & IFF_SLAVE)
   			break;
   

@@ -3244,8 +3245,10 @@ static int addrconf_notify(struct notifier_block *this, unsigned long event,
   
   		if (!idev && dev->mtu >= IPV6_MIN_MTU) {
   			idev = ipv6_add_dev(dev);
-			if (!IS_ERR(idev))
-				break;
+			if (!IS_ERR(idev)) {
+				event = NETDEV_UP;
+				goto netdev_change;
+			}
   		}
   
   		/*

Seems like this code isn't quite correct.  You are calling ipv6_add_dev
for slave devices, and if I understand things correctly I don't believe
that was happening before and may be an unintended side effect.

Hmm, could you quickly help me where I get into this situation? I made
sure I enter the NETDEV_UP part before the IFF_SLAVE test and
disable_ipv6 te

I think I was getting a bit a head of myself.  I was looking over the 
NETDEV_UP code and thinking that we could just fall into that path since 
it is already calling ipv6_add_dev.  However now I am wondering if maybe 
we need to look at adding an idev allocation somewhere before the 
disable_ipv6 check.  I assume that is why you were allocating the idev 
before you were getting into NETDEV_UP?

quoted

You might want to instead just make it so that you only do the jump, and
perhaps change the code in the NETDEV_UP/NETDEV_CHANGE section so that
you test for NETDEV_CHANGE instead of NETDEV_UP.  That should be enough
to get the effect you are looking for and I believe there would be no
change to behaviour other than adding IPv6 link-local addresses when the
MTU is increased.

Give me a bit and I can submit an alternative that may actually work out
a bit better I think.

If you go the NETDEV_CHANGE route instead of NETDEV_UP, you end up with
the IF_READY flag already set from ipv6_add_dev and thus won't do any
initialization of the device.

What I meant was that you don't need to change the event.  If you change 
the check inside the NETDEV_UP/CHANGE code path so that it tests for 
event != NETDEV_CHANGE instead of event == NETDEV_UP you don't need to 
change the event type.

Sure, I wait.

Might be a bit longer.  I just realized that I think there is another 
bug here where you are going through the NETDEV_UP path even though the 
interface isn't up.  I'll run through some testing this morning to work 
out the kinks.

- Alex

Hi Alex,

On Mon, Oct 26, 2015, at 18:07, Alexander Duyck wrote:

quoted

quoted

Seems like this code isn't quite correct.  You are calling ipv6_add_dev
for slave devices, and if I understand things correctly I don't believe
that was happening before and may be an unintended side effect.

Hmm, could you quickly help me where I get into this situation? I made
sure I enter the NETDEV_UP part before the IFF_SLAVE test and
disable_ipv6 te

I think I was getting a bit a head of myself.  I was looking over the 
NETDEV_UP code and thinking that we could just fall into that path since 
it is already calling ipv6_add_dev.  However now I am wondering if maybe 
we need to look at adding an idev allocation somewhere before the 
disable_ipv6 check.  I assume that is why you were allocating the idev 
before you were getting into NETDEV_UP?

The original bug report was:

If user reduces the MTU below IPV6_MIN_MTU we addrconf_ifdown the
interface but don't reinitialize the interface if the MTU is increased
later on.

quoted

quoted

You might want to instead just make it so that you only do the jump, and
perhaps change the code in the NETDEV_UP/NETDEV_CHANGE section so that
you test for NETDEV_CHANGE instead of NETDEV_UP.  That should be enough
to get the effect you are looking for and I believe there would be no
change to behaviour other than adding IPv6 link-local addresses when the
MTU is increased.

Give me a bit and I can submit an alternative that may actually work out
a bit better I think.

If you go the NETDEV_CHANGE route instead of NETDEV_UP, you end up with
the IF_READY flag already set from ipv6_add_dev and thus won't do any
initialization of the device.

What I meant was that you don't need to change the event.  If you change 
the check inside the NETDEV_UP/CHANGE code path so that it tests for 
event != NETDEV_CHANGE instead of event == NETDEV_UP you don't need to 
change the event type.

Yeah, that would be possible, too. I just find an equal easier to
follow. ;)

quoted

Sure, I wait.

Might be a bit longer.  I just realized that I think there is another 
bug here where you are going through the NETDEV_UP path even though the 
interface isn't up.  I'll run through some testing this morning to work 
out the kinks.

Ok, cool. I have a look at it again, too.

Bye,
Hannes

This change makes it so that we reinitialize the interface if the MTU is
increased back above IPV6_MIN_MTU and the interface is up.

Cc: Hannes Frederic Sowa <redacted>
Signed-off-by: Alexander Duyck <redacted>
---
 net/ipv6/addrconf.c |   46 +++++++++++++++++++++++++++-------------------
 1 file changed, 27 insertions(+), 19 deletions(-)

diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index d0c685cdc345..d72fa90d6feb 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c

@@ -3147,6 +3147,32 @@ static int addrconf_notify(struct notifier_block *this, unsigned long event,
 		}
 		break;
 
+	case NETDEV_CHANGEMTU:
+		/* if MTU under IPV6_MIN_MTU stop IPv6 on this interface. */
+		if (dev->mtu < IPV6_MIN_MTU) {
+			addrconf_ifdown(dev, 1);
+			break;
+		}
+
+		if (idev) {
+			rt6_mtu_change(dev, dev->mtu);
+			idev->cnf.mtu6 = dev->mtu;
+			break;
+		}
+
+		/* allocate new idev */
+		idev = ipv6_add_dev(dev);
+		if (IS_ERR(idev))
+			break;
+
+		/* device is still not ready */
+		if (!(idev->if_flags & IF_READY))
+			break;
+
+		run_pending = 1;
+
+		/* fall through */
+
 	case NETDEV_UP:
 	case NETDEV_CHANGE:
 		if (dev->flags & IFF_SLAVE)

@@ -3170,7 +3196,7 @@ static int addrconf_notify(struct notifier_block *this, unsigned long event,
 				idev->if_flags |= IF_READY;
 				run_pending = 1;
 			}
-		} else {
+		} else if (event == NETDEV_CHANGE) {
 			if (!addrconf_qdisc_ok(dev)) {
 				/* device is still not ready. */
 				break;

@@ -3235,24 +3261,6 @@ static int addrconf_notify(struct notifier_block *this, unsigned long event,
 		}
 		break;
 
-	case NETDEV_CHANGEMTU:
-		if (idev && dev->mtu >= IPV6_MIN_MTU) {
-			rt6_mtu_change(dev, dev->mtu);
-			idev->cnf.mtu6 = dev->mtu;
-			break;
-		}
-
-		if (!idev && dev->mtu >= IPV6_MIN_MTU) {
-			idev = ipv6_add_dev(dev);
-			if (!IS_ERR(idev))
-				break;
-		}
-
-		/*
-		 * if MTU under IPV6_MIN_MTU.
-		 * Stop IPv6 on this interface.
-		 */
-
 	case NETDEV_DOWN:
 	case NETDEV_UNREGISTER:
 		/*

Hi Alex,

On Mon, Oct 26, 2015, at 18:07, Alexander Duyck wrote:

Might be a bit longer.  I just realized that I think there is another 
bug here where you are going through the NETDEV_UP path even though the 
interface isn't up.  I'll run through some testing this morning to work 
out the kinks.

When you wrote this, I noticed that if someone removes the LL addresses
to disable the interface and raises the MTU again, we would also start
adding link-local addresses. Probably we need to safe the last state of
disable_ipv6 somewhere in the parent interface. :(

Maybe there is an easier solution for that.

Thanks for your patch, it looks cleaner!

Bye,
Hannes

Hannes Frederic Sowa [off-list ref] wrote:

Hello Alex,

On Mon, Oct 26, 2015, at 16:52, Alexander Duyck wrote:

quoted

Seems like this code isn't quite correct.  You are calling ipv6_add_dev 
for slave devices, and if I understand things correctly I don't believe 
that was happening before and may be an unintended side effect.

Ah, btw., autoconf and ipv6 operation on IFF_SLAVE devices is actually
desired nowadays and don't think we can change this. See also:
<https://patchwork.ozlabs.org/patch/531196/>

	IPv6 addrconf on IFF_SLAVE devices was disabled for bonding
slaves in commit c2edacf80e15 because it caused issues with snooping
switches.

	This is also referenced in

https://bugzilla.redhat.com/show_bug.cgi?id=236750

	Won't re-enabling autoconf on IFF_SLAVE devices cause that issue
to return?

	-J

---
	-Jay Vosburgh, jay.vosburgh@canonical.com

Hi,

On Mon, Oct 26, 2015, at 20:16, Jay Vosburgh wrote:

Hannes Frederic Sowa [off-list ref] wrote:

quoted

Hello Alex,

On Mon, Oct 26, 2015, at 16:52, Alexander Duyck wrote:

quoted

Seems like this code isn't quite correct.  You are calling ipv6_add_dev 
for slave devices, and if I understand things correctly I don't believe 
that was happening before and may be an unintended side effect.

Ah, btw., autoconf and ipv6 operation on IFF_SLAVE devices is actually
desired nowadays and don't think we can change this. See also:
<https://patchwork.ozlabs.org/patch/531196/>

	IPv6 addrconf on IFF_SLAVE devices was disabled for bonding
slaves in commit c2edacf80e15 because it caused issues with snooping
switches.

	This is also referenced in

https://bugzilla.redhat.com/show_bug.cgi?id=236750

	Won't re-enabling autoconf on IFF_SLAVE devices cause that issue
to return?

Both patches don't enable autoconf on IFF_SLAVE devices. Sorry for being
imprecise. The referred patch was changing the behavior to whether the
device had a master device.

@Alex, I will take your patch and submit it with the necessary guards to
not enable ipv6 again if we forcefully disable ipv6 and later on shrink
and increase the MTU again. I will do so in your name. Thanks again for
the patch!

Bye,
Hannes

On 10/26/2015 01:45 PM, Hannes Frederic Sowa wrote:

Hi,

On Mon, Oct 26, 2015, at 20:16, Jay Vosburgh wrote:

quoted

Hannes Frederic Sowa [off-list ref] wrote:

quoted

Hello Alex,

On Mon, Oct 26, 2015, at 16:52, Alexander Duyck wrote:

quoted

Seems like this code isn't quite correct.  You are calling ipv6_add_dev
for slave devices, and if I understand things correctly I don't believe
that was happening before and may be an unintended side effect.

Ah, btw., autoconf and ipv6 operation on IFF_SLAVE devices is actually
desired nowadays and don't think we can change this. See also:
<https://patchwork.ozlabs.org/patch/531196/>

	IPv6 addrconf on IFF_SLAVE devices was disabled for bonding
slaves in commit c2edacf80e15 because it caused issues with snooping
switches.

	This is also referenced in

https://bugzilla.redhat.com/show_bug.cgi?id=236750

	Won't re-enabling autoconf on IFF_SLAVE devices cause that issue
to return?

Both patches don't enable autoconf on IFF_SLAVE devices. Sorry for being
imprecise. The referred patch was changing the behavior to whether the
device had a master device.

Yes, the IFF_SLAVE comment on my part was an error in interpretation of 
the code.

@Alex, I will take your patch and submit it with the necessary guards to
not enable ipv6 again if we forcefully disable ipv6 and later on shrink
and increase the MTU again. I will do so in your name. Thanks again for
the patch!

No problem.  If you want to you can take over authorship of the patch 
and just leave my signed-off-by on there.  I'm good either way.

- Alex

From: Alexander Duyck <redacted>
Date: Mon, 26 Oct 2015 11:06:33 -0700

This change makes it so that we reinitialize the interface if the MTU is
increased back above IPV6_MIN_MTU and the interface is up.

Cc: Hannes Frederic Sowa <redacted>
Signed-off-by: Alexander Duyck <redacted>

Applied, thanks.