netdev - [PATCH] Set DF bit for IPv4 GRE tunnels with fixed TTL

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Message-ID: <56634F31.3000609@shemyak.com>
Date:	Sat, 5 Dec 2015 22:55:13 +0200
From:	Konstantin Shemyak <konstantin@...myak.com>
To:	David Miller <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	Hannes Frederic Sowa <hannes@...essinduktion.org>,
	pshelar@...ira.com
Subject: [PATCH] Set DF bit for IPv4 GRE tunnels with fixed TTL

The DF bit on IPv4 GRE tunnels with fixed TTL is enforced in order
to prevent networking loops. This was the original behavior of GRE
tunnels, lost in the refactoring.

Signed-off-by: Konstantin Shemyak <konstantin@...myak.com>
---
  net/ipv4/ip_gre.c | 4 ++++
  1 file changed, 4 insertions(+)

diff --git a/net/ipv4/ip_gre.c b/net/ipv4/ip_gre.c
index 6145214..485bf27 100644
--- a/net/ipv4/ip_gre.c
+++ b/net/ipv4/ip_gre.c
@@ -679,6 +679,10 @@ static int ipgre_tunnel_ioctl(struct net_device *dev,
  		    ((p.i_flags|p.o_flags)&(GRE_VERSION|GRE_ROUTING)))
  			return -EINVAL;
  	}
+
+        if (p.iph.ttl)
+                p.iph.frag_off |= htons(IP_DF);
+
  	p.i_flags = gre_flags_to_tnl_flags(p.i_flags);
  	p.o_flags = gre_flags_to_tnl_flags(p.o_flags);

-- 
1.9.1

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