netdev - [PATCH net 3/3] vti6: Fix dev->max

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Message-Id: <c16e0160ee25001c4521d2d92f438b047b165d28.1521128962.git.sbrivio@redhat.com>
Date:   Thu, 15 Mar 2018 17:17:13 +0100
From:   Stefano Brivio <sbrivio@...hat.com>
To:     "David S . Miller" <davem@...emloft.net>
Cc:     Sabrina Dubroca <sd@...asysnail.net>,
        Steffen Klassert <steffen.klassert@...unet.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Alexey Kodanev <alexey.kodanev@...cle.com>,
        Jarod Wilson <jarod@...hat.com>, netdev@...r.kernel.org
Subject: [PATCH net 3/3] vti6: Fix dev->max_mtu setting

We shouldn't allow a tunnel to have IP_MAX_MTU as MTU, because
another IPv6 header is going on top of our packets. Without this
patch, we might end up building packets bigger than IP_MAX_MTU.

Fixes: b96f9afee4eb ("ipv4/6: use core net MTU range checking")
Signed-off-by: Stefano Brivio <sbrivio@...hat.com>
Acked-by: Sabrina Dubroca <sd@...asysnail.net>
---
 net/ipv6/ip6_vti.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ipv6/ip6_vti.c b/net/ipv6/ip6_vti.c
index 971175142e14..ce18cd20389d 100644
--- a/net/ipv6/ip6_vti.c
+++ b/net/ipv6/ip6_vti.c
@@ -879,7 +879,7 @@ static void vti6_dev_setup(struct net_device *dev)
 
 	dev->type = ARPHRD_TUNNEL6;
 	dev->min_mtu = IPV6_MIN_MTU;
-	dev->max_mtu = IP_MAX_MTU;
+	dev->max_mtu = IP_MAX_MTU - sizeof(struct ipv6hdr);
 	dev->flags |= IFF_NOARP;
 	dev->addr_len = sizeof(struct in6_addr);
 	netif_keep_dst(dev);
-- 
2.15.1