net: ip: add skb drop reasons to ip forwarding

Replace kfree_skb() which is used in ip6_forward() and ip_forward()
with kfree_skb_reason().

The new drop reason 'SKB_DROP_REASON_PKT_TOO_BIG' is introduced for
the case that the length of the packet exceeds MTU and can't
fragment.
Signed-off-by: Menglong Dong <imagedong@tencent.com>
Reviewed-by: Jiang Biao <benbjiang@tencent.com>
Reviewed-by: Hao Peng <flyingpeng@tencent.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/skbuff.h

@@ -453,6 +453,9 @@ enum skb_drop_reason {
 	SKB_DROP_REASON_IP_INNOROUTES,	/* network unreachable, corresponding
 					 * to IPSTATS_MIB_INADDRERRORS
 					 */
+	SKB_DROP_REASON_PKT_TOO_BIG,	/* packet size is too big (maybe exceed
+					 * the MTU)
+					 */
 	SKB_DROP_REASON_MAX,
 };
 

include/trace/events/skb.h

@@ -65,6 +65,7 @@
 	EM(SKB_DROP_REASON_INVALID_PROTO, INVALID_PROTO)	\
 	EM(SKB_DROP_REASON_IP_INADDRERRORS, IP_INADDRERRORS)	\
 	EM(SKB_DROP_REASON_IP_INNOROUTES, IP_INNOROUTES)	\
+	EM(SKB_DROP_REASON_PKT_TOO_BIG, PKT_TOO_BIG)		\
 	EMe(SKB_DROP_REASON_MAX, MAX)
 
 #undef EM

net/ipv4/ip_forward.c

@@ -90,6 +90,7 @@ int ip_forward(struct sk_buff *skb)
 	struct rtable *rt;	/* Route we use */
 	struct ip_options *opt	= &(IPCB(skb)->opt);
 	struct net *net;
+	SKB_DR(reason);
 
 	/* that should never happen */
 	if (skb->pkt_type != PACKET_HOST)
@@ -101,8 +102,10 @@ int ip_forward(struct sk_buff *skb)
 	if (skb_warn_if_lro(skb))
 		goto drop;
 
-	if (!xfrm4_policy_check(NULL, XFRM_POLICY_FWD, skb))
+	if (!xfrm4_policy_check(NULL, XFRM_POLICY_FWD, skb)) {
+		SKB_DR_SET(reason, XFRM_POLICY);
 		goto drop;
+	}
 
 	if (IPCB(skb)->opt.router_alert && ip_call_ra_chain(skb))
 		return NET_RX_SUCCESS;
@@ -118,8 +121,10 @@ int ip_forward(struct sk_buff *skb)
 	if (ip_hdr(skb)->ttl <= 1)
 		goto too_many_hops;
 
-	if (!xfrm4_route_forward(skb))
+	if (!xfrm4_route_forward(skb)) {
+		SKB_DR_SET(reason, XFRM_POLICY);
 		goto drop;
+	}
 
 	rt = skb_rtable(skb);
 
@@ -132,6 +137,7 @@ int ip_forward(struct sk_buff *skb)
 		IP_INC_STATS(net, IPSTATS_MIB_FRAGFAILS);
 		icmp_send(skb, ICMP_DEST_UNREACH, ICMP_FRAG_NEEDED,
 			  htonl(mtu));
+		SKB_DR_SET(reason, PKT_TOO_BIG);
 		goto drop;
 	}
 
@@ -169,7 +175,8 @@ int ip_forward(struct sk_buff *skb)
 	/* Tell the sender its packet died... */
 	__IP_INC_STATS(net, IPSTATS_MIB_INHDRERRORS);
 	icmp_send(skb, ICMP_TIME_EXCEEDED, ICMP_EXC_TTL, 0);
+	SKB_DR_SET(reason, IP_INHDR);
 drop:
-	kfree_skb(skb);
+	kfree_skb_reason(skb, reason);
 	return NET_RX_DROP;
 }

net/ipv6/ip6_output.c

@@ -469,6 +469,7 @@ int ip6_forward(struct sk_buff *skb)
 	struct inet6_skb_parm *opt = IP6CB(skb);
 	struct net *net = dev_net(dst->dev);
 	struct inet6_dev *idev;
+	SKB_DR(reason);
 	u32 mtu;
 
 	idev = __in6_dev_get_safely(dev_get_by_index_rcu(net, IP6CB(skb)->iif));
@@ -518,7 +519,7 @@ int ip6_forward(struct sk_buff *skb)
 		icmpv6_send(skb, ICMPV6_TIME_EXCEED, ICMPV6_EXC_HOPLIMIT, 0);
 		__IP6_INC_STATS(net, idev, IPSTATS_MIB_INHDRERRORS);
 
-		kfree_skb(skb);
+		kfree_skb_reason(skb, SKB_DROP_REASON_IP_INHDR);
 		return -ETIMEDOUT;
 	}
 
@@ -537,6 +538,7 @@ int ip6_forward(struct sk_buff *skb)
 
 	if (!xfrm6_route_forward(skb)) {
 		__IP6_INC_STATS(net, idev, IPSTATS_MIB_INDISCARDS);
+		SKB_DR_SET(reason, XFRM_POLICY);
 		goto drop;
 	}
 	dst = skb_dst(skb);
@@ -596,7 +598,7 @@ int ip6_forward(struct sk_buff *skb)
 		__IP6_INC_STATS(net, idev, IPSTATS_MIB_INTOOBIGERRORS);
 		__IP6_INC_STATS(net, ip6_dst_idev(dst),
 				IPSTATS_MIB_FRAGFAILS);
-		kfree_skb(skb);
+		kfree_skb_reason(skb, SKB_DROP_REASON_PKT_TOO_BIG);
 		return -EMSGSIZE;
 	}
 
@@ -618,8 +620,9 @@ int ip6_forward(struct sk_buff *skb)
 
 error:
 	__IP6_INC_STATS(net, idev, IPSTATS_MIB_INADDRERRORS);
+	SKB_DR_SET(reason, IP_INADDRERRORS);
 drop:
-	kfree_skb(skb);
+	kfree_skb_reason(skb, reason);
 	return -EINVAL;
 }