net: don't call update_pmtu unconditionally

Some dst_ops (e.g. md_dst_ops)) doesn't set this handler. It may result to:
"BUG: unable to handle kernel NULL pointer dereference at           (null)"

Let's add a helper to check if update_pmtu is available before calling it.

Fixes: 52a589d51f10 ("geneve: update skb dst pmtu on tx path")
Fixes: a93bf0ff4490 ("vxlan: update skb dst pmtu on tx path")
CC: Roman Kapl <code@rkapl.cz>
CC: Xin Long <lucien.xin@gmail.com>
Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

9 files changed, 20 insertions, 18 deletions

diff --git a/drivers/infiniband/ulp/ipoib/ipoib_cm.c b/drivers/infiniband/ulp/ipoib/ipoib_cm.c
index 2c13123bfd69..71ea9e26666c 100644
--- a/drivers/infiniband/ulp/ipoib/ipoib_cm.c
+++ b/drivers/infiniband/ulp/ipoib/ipoib_cm.c
@@ -1456,8 +1456,7 @@ void ipoib_cm_skb_too_long(struct net_device *dev, struct sk_buff *skb,
         struct ipoib_dev_priv *priv = ipoib_priv(dev);
         int e = skb_queue_empty(&priv->cm.skb_queue);
 
-        if (skb_dst(skb))
-                skb_dst(skb)->ops->update_pmtu(skb_dst(skb), NULL, skb, mtu);
+        skb_dst_update_pmtu(skb, mtu);
 
         skb_queue_tail(&priv->cm.skb_queue, skb);
         if (e)
diff --git a/drivers/net/geneve.c b/drivers/net/geneve.c
index 0a48b3073d3d..64fda2e1040e 100644
--- a/drivers/net/geneve.c
+++ b/drivers/net/geneve.c
@@ -829,7 +829,7 @@ static int geneve_xmit_skb(struct sk_buff *skb, struct net_device *dev,
                 int mtu = dst_mtu(&rt->dst) - sizeof(struct iphdr) -
                           GENEVE_BASE_HLEN - info->options_len - 14;
 
-                skb_dst(skb)->ops->update_pmtu(skb_dst(skb), NULL, skb, mtu);
+                skb_dst_update_pmtu(skb, mtu);
         }
 
         sport = udp_flow_src_port(geneve->net, skb, 1, USHRT_MAX, true);
@@ -875,7 +875,7 @@ static int geneve6_xmit_skb(struct sk_buff *skb, struct net_device *dev,
                 int mtu = dst_mtu(dst) - sizeof(struct ipv6hdr) -
                           GENEVE_BASE_HLEN - info->options_len - 14;
 
-                skb_dst(skb)->ops->update_pmtu(skb_dst(skb), NULL, skb, mtu);
+                skb_dst_update_pmtu(skb, mtu);
         }
 
         sport = udp_flow_src_port(geneve->net, skb, 1, USHRT_MAX, true);
diff --git a/drivers/net/vxlan.c b/drivers/net/vxlan.c
index 31f4b7911ef8..c3e34e3c82a7 100644
--- a/drivers/net/vxlan.c
+++ b/drivers/net/vxlan.c
@@ -2158,8 +2158,7 @@ static void vxlan_xmit_one(struct sk_buff *skb, struct net_device *dev,
                 if (skb_dst(skb)) {
                         int mtu = dst_mtu(ndst) - VXLAN_HEADROOM;
 
-                        skb_dst(skb)->ops->update_pmtu(skb_dst(skb), NULL,
-                                                       skb, mtu);
+                        skb_dst_update_pmtu(skb, mtu);
                 }
 
                 tos = ip_tunnel_ecn_encap(tos, old_iph, skb);
@@ -2200,8 +2199,7 @@ static void vxlan_xmit_one(struct sk_buff *skb, struct net_device *dev,
                 if (skb_dst(skb)) {
                         int mtu = dst_mtu(ndst) - VXLAN6_HEADROOM;
 
-                        skb_dst(skb)->ops->update_pmtu(skb_dst(skb), NULL,
-                                                       skb, mtu);
+                        skb_dst_update_pmtu(skb, mtu);
                 }
 
                 tos = ip_tunnel_ecn_encap(tos, old_iph, skb);
diff --git a/include/net/dst.h b/include/net/dst.h
index b091fd536098..d49d607dd2b3 100644
--- a/include/net/dst.h
+++ b/include/net/dst.h
@@ -521,4 +521,12 @@ static inline struct xfrm_state *dst_xfrm(const struct dst_entry *dst)
 }
 #endif
 
+static inline void skb_dst_update_pmtu(struct sk_buff *skb, u32 mtu)
+{
+        struct dst_entry *dst = skb_dst(skb);
+
+        if (dst && dst->ops->update_pmtu)
+                dst->ops->update_pmtu(dst, NULL, skb, mtu);
+}
+
 #endif /* _NET_DST_H */
diff --git a/net/ipv4/ip_tunnel.c b/net/ipv4/ip_tunnel.c
index 5ddb1cb52bd4..6d21068f9b55 100644
--- a/net/ipv4/ip_tunnel.c
+++ b/net/ipv4/ip_tunnel.c
@@ -520,8 +520,7 @@ static int tnl_update_pmtu(struct net_device *dev, struct sk_buff *skb,
         else
                 mtu = skb_dst(skb) ? dst_mtu(skb_dst(skb)) : dev->mtu;
 
-        if (skb_dst(skb))
-                skb_dst(skb)->ops->update_pmtu(skb_dst(skb), NULL, skb, mtu);
+        skb_dst_update_pmtu(skb, mtu);
 
         if (skb->protocol == htons(ETH_P_IP)) {
                 if (!skb_is_gso(skb) &&
diff --git a/net/ipv4/ip_vti.c b/net/ipv4/ip_vti.c
index 949f432a5f04..51b1669334fe 100644
--- a/net/ipv4/ip_vti.c
+++ b/net/ipv4/ip_vti.c
@@ -200,7 +200,7 @@ static netdev_tx_t vti_xmit(struct sk_buff *skb, struct net_device *dev,
 
         mtu = dst_mtu(dst);
         if (skb->len > mtu) {
-                skb_dst(skb)->ops->update_pmtu(skb_dst(skb), NULL, skb, mtu);
+                skb_dst_update_pmtu(skb, mtu);
                 if (skb->protocol == htons(ETH_P_IP)) {
                         icmp_send(skb, ICMP_DEST_UNREACH, ICMP_FRAG_NEEDED,
                                   htonl(mtu));
diff --git a/net/ipv6/ip6_tunnel.c b/net/ipv6/ip6_tunnel.c
index 9a7cf355bc8c..1ee5584c3555 100644
--- a/net/ipv6/ip6_tunnel.c
+++ b/net/ipv6/ip6_tunnel.c
@@ -642,8 +642,7 @@ ip4ip6_err(struct sk_buff *skb, struct inet6_skb_parm *opt,
                 if (rel_info > dst_mtu(skb_dst(skb2)))
                         goto out;
 
-                skb_dst(skb2)->ops->update_pmtu(skb_dst(skb2), NULL, skb2,
-                                                rel_info);
+                skb_dst_update_pmtu(skb2, rel_info);
         }
 
         icmp_send(skb2, rel_type, rel_code, htonl(rel_info));
@@ -1131,8 +1130,7 @@ route_lookup:
                 mtu = 576;
         }
 
-        if (skb_dst(skb) && !t->parms.collect_md)
-                skb_dst(skb)->ops->update_pmtu(skb_dst(skb), NULL, skb, mtu);
+        skb_dst_update_pmtu(skb, mtu);
         if (skb->len - t->tun_hlen - eth_hlen > mtu && !skb_is_gso(skb)) {
                 *pmtu = mtu;
                 err = -EMSGSIZE;
diff --git a/net/ipv6/ip6_vti.c b/net/ipv6/ip6_vti.c
index dbb74f3c57a7..8c184f84f353 100644
--- a/net/ipv6/ip6_vti.c
+++ b/net/ipv6/ip6_vti.c
@@ -483,7 +483,7 @@ vti6_xmit(struct sk_buff *skb, struct net_device *dev, struct flowi *fl)
 
         mtu = dst_mtu(dst);
         if (!skb->ignore_df && skb->len > mtu) {
-                skb_dst(skb)->ops->update_pmtu(dst, NULL, skb, mtu);
+                skb_dst_update_pmtu(skb, mtu);
 
                 if (skb->protocol == htons(ETH_P_IPV6)) {
                         if (mtu < IPV6_MIN_MTU)
diff --git a/net/ipv6/sit.c b/net/ipv6/sit.c
index d7dc23c1b2ca..3873d3877135 100644
--- a/net/ipv6/sit.c
+++ b/net/ipv6/sit.c
@@ -934,8 +934,8 @@ static netdev_tx_t ipip6_tunnel_xmit(struct sk_buff *skb,
                         df = 0;
                 }
 
-                if (tunnel->parms.iph.daddr && skb_dst(skb))
-                        skb_dst(skb)->ops->update_pmtu(skb_dst(skb), NULL, skb, mtu);
+                if (tunnel->parms.iph.daddr)
+                        skb_dst_update_pmtu(skb, mtu);
 
                 if (skb->len > mtu && !skb_is_gso(skb)) {
                         icmpv6_send(skb, ICMPV6_PKT_TOOBIG, 0, mtu);