New: Route advmss copied to ALL routes when interface MTU changes

Bugme-new In review Andrew Morton 3 participants 4 messages Jul 15, 2007 – Jul 26, 2007 1 message not in the archive

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Andrew Morton

author

2007-07-15 04:48 UTC #1 lore raw

Quoted 1 line · On Sat, 14 Jul 2007 15:34:31 -0700 (PDT) [email protected] wrote:

http://bugzilla.kernel.org/show_bug.cgi?id=8756

It is unclear which kernel version this applies to?

Quoted 49 lines

Summary: Route advmss copied to ALL routes when interface MTU
changes
Product: Networking
Version: 2.5
Platform: All
OS/Version: Linux
Tree: Mainline
Status: NEW
Severity: normal
Priority: P1
Component: IPV6
AssignedTo: [email protected]
ReportedBy: [email protected]
Steps to reproduce:
1. Have multiple network devices and routes for them with standard (low, i.e. 1500) MTUs and default ADVMSS (e.g. 1440)
2. Change the MTU on one of them to something high (e.g. 7200)
3. The ADVMSS is incorrectly set for ALL routes based on the new MTU of the interface that changed.
Note: if addrconf is running then the ADVMSS will be reset on the next RA, so this will impede attempts to reproduce.
# ip -6 r
fe80::/64 dev sit0  metric 256  expires 4481744sec mtu 1480 advmss 1440
hoplimit 4294967295
fe80::/64 dev ppp0  metric 256  expires 19071345sec mtu 1500 advmss 1440
hoplimit 4294967295
fe80::/64 dev eth0  metric 256  expires 19072430sec mtu 1500 advmss 1440
hoplimit 4294967295
default dev ppp0  metric 1024  expires 19071347sec mtu 1500 advmss 1440
hoplimit 4294967295
# ifconfig eth0 mtu 7200
# ip -6 r
fe80::/64 dev sit0  metric 256  expires 4481732sec mtu 1480 advmss 7140
hoplimit 4294967295 <-- wrong
fe80::/64 dev ppp0  metric 256  expires 19071334sec mtu 1500 advmss 7140
hoplimit 4294967295 <-- wrong
fe80::/64 dev eth0  metric 256  expires 19072419sec mtu 7200 advmss 7140
hoplimit 4294967295 <-- correct
Explicitly setting the MTU on these other routes (although this is not possible without having to add another route due to bug 8755) automatically sets ADVMSS appropriately.

Simon Arlott

2007-07-15 08:07 UTC #2 lore raw

Quoted 5 lines · Andrew Morton

Quoted 1 line · On Sat, 14 Jul 2007 15:34:31 -0700 (PDT) [email protected] wrote:
http://bugzilla.kernel.org/show_bug.cgi?id=8756
It is unclear which kernel version this applies to?

Linus' 2.6 tree, as of Mon Jul 9 15:50:56 2007 -0700

For some reason it says "Version: 2.5" on the email and "Version: " on the website...

Quoted 50 lines

Quoted 50 lines
Summary: Route advmss copied to ALL routes when interface MTU
changes
Product: Networking
Version: 2.5
Platform: All
OS/Version: Linux
Tree: Mainline
Status: NEW
Severity: normal
Priority: P1
Component: IPV6
AssignedTo: [email protected]
ReportedBy: [email protected]
Steps to reproduce:
1. Have multiple network devices and routes for them with standard (low, i.e. 1500) MTUs and default ADVMSS (e.g. 1440)
2. Change the MTU on one of them to something high (e.g. 7200)
3. The ADVMSS is incorrectly set for ALL routes based on the new MTU of the interface that changed.
Note: if addrconf is running then the ADVMSS will be reset on the next RA, so this will impede attempts to reproduce.
# ip -6 r
fe80::/64 dev sit0  metric 256  expires 4481744sec mtu 1480 advmss 1440
hoplimit 4294967295
fe80::/64 dev ppp0  metric 256  expires 19071345sec mtu 1500 advmss 1440
hoplimit 4294967295
fe80::/64 dev eth0  metric 256  expires 19072430sec mtu 1500 advmss 1440
hoplimit 4294967295
default dev ppp0  metric 1024  expires 19071347sec mtu 1500 advmss 1440
hoplimit 4294967295
# ifconfig eth0 mtu 7200
# ip -6 r
fe80::/64 dev sit0  metric 256  expires 4481732sec mtu 1480 advmss 7140
hoplimit 4294967295 <-- wrong
fe80::/64 dev ppp0  metric 256  expires 19071334sec mtu 1500 advmss 7140
hoplimit 4294967295 <-- wrong
fe80::/64 dev eth0  metric 256  expires 19072419sec mtu 7200 advmss 7140
hoplimit 4294967295 <-- correct
Explicitly setting the MTU on these other routes (although this is not possible without having to add another route due to bug 8755) automatically sets ADVMSS appropriately.

Signature · 1 line

Simon Arlott

Simon Arlott

2007-07-23 19:25 UTC #3 lore raw

PATCH 1/1 ] IPv6: Don't update ADVMSS on routes where the MTU is not also updated

The ADVMSS value was incorrectly updated for ALL routes when the MTU is updated because it's outside the effect of the if statement's condition.

Signed-off-by Simon Arlott <[email protected]>

---
This fixes http://bugzilla.kernel.org/show_bug.cgi?id=8756

 net/ipv6/route.c |    5 +++--
 1 files changed, 3 insertions(+), 2 deletions(-)

net/ipv6/route.c +3 -2

index 919de68..55ea80f 100644
@@ -1983,9 +1983,10 @@ static int rt6_mtu_change_route(struct rt6_info *rt, void *p_arg)
 	    !dst_metric_locked(&rt->u.dst, RTAX_MTU) &&
 	    (dst_mtu(&rt->u.dst) > arg->mtu ||
 	     (dst_mtu(&rt->u.dst) < arg->mtu &&
-	      dst_mtu(&rt->u.dst) == idev->cnf.mtu6)))
+	      dst_mtu(&rt->u.dst) == idev->cnf.mtu6))) {
 		rt->u.dst.metrics[RTAX_MTU-1] = arg->mtu;
-	rt->u.dst.metrics[RTAX_ADVMSS-1] = ipv6_advmss(arg->mtu);
+		rt->u.dst.metrics[RTAX_ADVMSS-1] = ipv6_advmss(arg->mtu);
+	}
 	return 0;
 }

Signature · 4 lines

1.5.0.1

-- 
Simon Arlott

David Miller

maintainer

2007-07-26 07:10 UTC #4 lore raw

Re: [PATCH [Bug 8756]] IPv6: Don't update ADVMSS on routes where the MTU is not also updated

From: Simon Arlott <[email protected]>
Date: Mon, 23 Jul 2007 20:25:45 +0100

Quoted 5 lines

The ADVMSS value was incorrectly updated for ALL routes when the MTU is updated because it's outside the effect of the if statement's condition.
Signed-off-by Simon Arlott <[email protected]>

Thanks for fixing this bug Simon, patch applied.