net: Discard and warn about LRO'd skbs received for forwarding

Add skb_warn_if_lro() to test whether an skb was received with LRO and
warn if so.

Change br_forward(), ip_forward() and ip6_forward() to call it) and
discard the skb if it returns true.
Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/skbuff.h

@@ -1702,6 +1702,20 @@ static inline int skb_is_gso_v6(const struct sk_buff *skb)
 	return skb_shinfo(skb)->gso_type & SKB_GSO_TCPV6;
 }
 
+extern void __skb_warn_lro_forwarding(const struct sk_buff *skb);
+
+static inline bool skb_warn_if_lro(const struct sk_buff *skb)
+{
+	/* LRO sets gso_size but not gso_type, whereas if GSO is really
+	 * wanted then gso_type will be set. */
+	struct skb_shared_info *shinfo = skb_shinfo(skb);
+	if (shinfo->gso_size != 0 && unlikely(shinfo->gso_type == 0)) {
+		__skb_warn_lro_forwarding(skb);
+		return true;
+	}
+	return false;
+}
+
 static inline void skb_forward_csum(struct sk_buff *skb)
 {
 	/* Unfortunately we don't support this one.  Any brave souls? */

net/bridge/br_forward.c

@@ -89,7 +89,7 @@ void br_deliver(const struct net_bridge_port *to, struct sk_buff *skb)
 /* called with rcu_read_lock */
 void br_forward(const struct net_bridge_port *to, struct sk_buff *skb)
 {
-	if (should_deliver(to, skb)) {
+	if (!skb_warn_if_lro(skb) && should_deliver(to, skb)) {
 		__br_forward(to, skb);
 		return;
 	}

net/core/skbuff.c

@@ -2583,6 +2583,13 @@ bool skb_partial_csum_set(struct sk_buff *skb, u16 start, u16 off)
 	return true;
 }
 
+void __skb_warn_lro_forwarding(const struct sk_buff *skb)
+{
+	if (net_ratelimit())
+		pr_warning("%s: received packets cannot be forwarded"
+			   " while LRO is enabled\n", skb->dev->name);
+}
+
 EXPORT_SYMBOL(___pskb_trim);
 EXPORT_SYMBOL(__kfree_skb);
 EXPORT_SYMBOL(kfree_skb);
@@ -2616,6 +2623,7 @@ EXPORT_SYMBOL(skb_seq_read);
 EXPORT_SYMBOL(skb_abort_seq_read);
 EXPORT_SYMBOL(skb_find_text);
 EXPORT_SYMBOL(skb_append_datato_frags);
+EXPORT_SYMBOL(__skb_warn_lro_forwarding);
 
 EXPORT_SYMBOL_GPL(skb_to_sgvec);
 EXPORT_SYMBOL_GPL(skb_cow_data);

net/ipv4/ip_forward.c

@@ -56,6 +56,9 @@ int ip_forward(struct sk_buff *skb)
 	struct rtable *rt;	/* Route we use */
 	struct ip_options * opt	= &(IPCB(skb)->opt);
 
+	if (skb_warn_if_lro(skb))
+		goto drop;
+
 	if (!xfrm4_policy_check(NULL, XFRM_POLICY_FWD, skb))
 		goto drop;
 

net/ipv6/ip6_output.c

@@ -407,6 +407,9 @@ int ip6_forward(struct sk_buff *skb)
 	if (ipv6_devconf.forwarding == 0)
 		goto error;
 
+	if (skb_warn_if_lro(skb))
+		goto drop;
+
 	if (!xfrm6_policy_check(NULL, XFRM_POLICY_FWD, skb)) {
 		IP6_INC_STATS(ip6_dst_idev(dst), IPSTATS_MIB_INDISCARDS);
 		goto drop;