netdev - Re: VLAN over GRE segfault

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Date:	Fri, 18 Mar 2011 11:27:27 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Diddi Oscarsson <diddi@...di.se>,
	David Miller <davem@...emloft.net>
Cc:	netdev@...r.kernel.org, Herbert Xu <herbert@...dor.apana.org.au>,
	Patrick McHardy <kaber@...sh.net>
Subject: Re: VLAN over GRE segfault

Le vendredi 18 mars 2011 à 08:34 +0100, Diddi Oscarsson a écrit :
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
> 
> Hello!
> 
> I was trying to get ethernet over GRE to work when I found an obvious
> way NOT to do it.
> Basically I created a VLAN interface from the GRE interface (even
> though I had my fair doubts it would work) which gave me a nice segfault.
> The problem with this is that after the segfault, new network
> connections cannot be made (ping, ssh, http, whatever) and a reboot of
> the computer is necessary.
> I think an error message needs to be added when trying an operation
> like this.
> 
> My system:
> Linux colalapp 2.6.37-2-amd64 #1 SMP Sun Feb 27 10:12:22 UTC 2011
> x86_64 GNU/Linux
> ip utility, iproute2-ss110107
> Debian unstable
> 
> Steps to reproduce:
> ip tunnel add gre0 mode gre
> ip link add link gre0 name vlan1 type vlan id 1
> ip link set vlan1 address 00:15:14:13:12:11
> ip link set gre0 up
> ip link set vlan1 up
> <CRASH>
> Attached in the mail is an output from dmesg right after the segfault.
> 
> Regarding ethernet over gre, I've just found out about gretap which
> I'm testing right now.

Hi Diddi

It might be a 2.6.28 regression, after commit c95b819ad7
(gre: Use needed_headroom)

Thanks

[PATCH] vlan: should take into account needed_headroom

Commit c95b819ad7 (gre: Use needed_headroom)
made gre use needed_headroom instead of hard_header_len

This uncover a bug in vlan code.

We should make sure vlan devices take into account their
real_dev->needed_headroom or we risk a crash in ipgre_header(), because
we dont have enough room to push IP header in skb.

Reported-by: Diddi Oscarsson <diddi@...di.se>
Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
Cc: Patrick McHardy <kaber@...sh.net>
Cc: Herbert Xu <herbert@...dor.apana.org.au>
---
 net/8021q/vlan_dev.c |    1 +
 1 files changed, 1 insertion(+)

diff --git a/net/8021q/vlan_dev.c b/net/8021q/vlan_dev.c
index ae610f0..e34ea9e 100644
--- a/net/8021q/vlan_dev.c
+++ b/net/8021q/vlan_dev.c
@@ -720,6 +720,7 @@ static int vlan_dev_init(struct net_device *dev)
 	dev->fcoe_ddp_xid = real_dev->fcoe_ddp_xid;
 #endif
 
+	dev->needed_headroom = real_dev->needed_headroom;
 	if (real_dev->features & NETIF_F_HW_VLAN_TX) {
 		dev->header_ops      = real_dev->header_ops;
 		dev->hard_header_len = real_dev->hard_header_len;


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