netdev - [PATCH net 2/2] geneve, vxlan: Don't set exceptions if skb->len

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Message-Id: <97f93a69894ed49e6b914a8211ec813cc1bbc433.1539381018.git.sbrivio@redhat.com>
Date:   Fri, 12 Oct 2018 23:53:59 +0200
From:   Stefano Brivio <sbrivio@...hat.com>
To:     "David S. Miller" <davem@...emloft.net>
Cc:     Xin Long <lucien.xin@...il.com>,
        Sabrina Dubroca <sd@...asysnail.net>, netdev@...r.kernel.org
Subject: [PATCH net 2/2] geneve, vxlan: Don't set exceptions if skb->len < mtu

We shouldn't abuse exceptions: if the destination MTU is already higher
than what we're transmitting, no exception should be created.

Fixes: 52a589d51f10 ("geneve: update skb dst pmtu on tx path")
Fixes: a93bf0ff4490 ("vxlan: update skb dst pmtu on tx path")
Signed-off-by: Stefano Brivio <sbrivio@...hat.com>
Reviewed-by: Sabrina Dubroca <sd@...asysnail.net>
---
 drivers/net/geneve.c |  7 +++----
 drivers/net/vxlan.c  |  4 ++--
 include/net/dst.h    | 10 ++++++++++
 3 files changed, 15 insertions(+), 6 deletions(-)

diff --git a/drivers/net/geneve.c b/drivers/net/geneve.c
index 61c4bfbeb41c..493cd382b8aa 100644
--- a/drivers/net/geneve.c
+++ b/drivers/net/geneve.c
@@ -830,8 +830,8 @@ static int geneve_xmit_skb(struct sk_buff *skb, struct net_device *dev,
 	if (IS_ERR(rt))
 		return PTR_ERR(rt);
 
-	skb_dst_update_pmtu(skb, dst_mtu(&rt->dst) -
-				 GENEVE_IPV4_HLEN - info->options_len);
+	skb_tunnel_check_pmtu(skb, &rt->dst,
+			      GENEVE_IPV4_HLEN + info->options_len);
 
 	sport = udp_flow_src_port(geneve->net, skb, 1, USHRT_MAX, true);
 	if (geneve->collect_md) {
@@ -872,8 +872,7 @@ static int geneve6_xmit_skb(struct sk_buff *skb, struct net_device *dev,
 	if (IS_ERR(dst))
 		return PTR_ERR(dst);
 
-	skb_dst_update_pmtu(skb, dst_mtu(dst) -
-				 GENEVE_IPV6_HLEN - info->options_len);
+	skb_tunnel_check_pmtu(skb, dst, GENEVE_IPV6_HLEN + info->options_len);
 
 	sport = udp_flow_src_port(geneve->net, skb, 1, USHRT_MAX, true);
 	if (geneve->collect_md) {
diff --git a/drivers/net/vxlan.c b/drivers/net/vxlan.c
index 22e0ce592e07..27bd586b94b0 100644
--- a/drivers/net/vxlan.c
+++ b/drivers/net/vxlan.c
@@ -2194,7 +2194,7 @@ static void vxlan_xmit_one(struct sk_buff *skb, struct net_device *dev,
 		}
 
 		ndst = &rt->dst;
-		skb_dst_update_pmtu(skb, dst_mtu(ndst) - VXLAN_HEADROOM);
+		skb_tunnel_check_pmtu(skb, ndst, VXLAN_HEADROOM);
 
 		tos = ip_tunnel_ecn_encap(tos, old_iph, skb);
 		ttl = ttl ? : ip4_dst_hoplimit(&rt->dst);
@@ -2231,7 +2231,7 @@ static void vxlan_xmit_one(struct sk_buff *skb, struct net_device *dev,
 				goto out_unlock;
 		}
 
-		skb_dst_update_pmtu(skb, dst_mtu(ndst) - VXLAN6_HEADROOM);
+		skb_tunnel_check_pmtu(skb, ndst, VXLAN6_HEADROOM);
 
 		tos = ip_tunnel_ecn_encap(tos, old_iph, skb);
 		ttl = ttl ? : ip6_dst_hoplimit(ndst);
diff --git a/include/net/dst.h b/include/net/dst.h
index 7f735e76ca73..6cf0870414c7 100644
--- a/include/net/dst.h
+++ b/include/net/dst.h
@@ -527,4 +527,14 @@ static inline void skb_dst_update_pmtu(struct sk_buff *skb, u32 mtu)
 		dst->ops->update_pmtu(dst, NULL, skb, mtu);
 }
 
+static inline void skb_tunnel_check_pmtu(struct sk_buff *skb,
+					 struct dst_entry *encap_dst,
+					 int headroom)
+{
+	u32 encap_mtu = dst_mtu(encap_dst);
+
+	if (skb->len > encap_mtu - headroom)
+		skb_dst_update_pmtu(skb, encap_mtu - headroom);
+}
+
 #endif /* _NET_DST_H */
-- 
2.19.1