net: dropreason: add SKB_DROP_REASON_DUP_FRAG

This is used to track when a duplicate segment received by various
reassembly units is dropped.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

include/net/dropreason.h

@@ -68,6 +68,7 @@
 	FN(IP_INADDRERRORS)		\
 	FN(IP_INNOROUTES)		\
 	FN(PKT_TOO_BIG)			\
+	FN(DUP_FRAG)			\
 	FNe(MAX)
 
 /**
@@ -300,6 +301,8 @@ enum skb_drop_reason {
 	 * MTU)
 	 */
 	SKB_DROP_REASON_PKT_TOO_BIG,
+	/** @SKB_DROP_REASON_DUP_FRAG: duplicate fragment */
+	SKB_DROP_REASON_DUP_FRAG,
 	/**
 	 * @SKB_DROP_REASON_MAX: the maximum of drop reason, which shouldn't be
 	 * used as a real 'reason'

net/ipv4/ip_fragment.c

@@ -278,10 +278,14 @@ static int ip_frag_queue(struct ipq *qp, struct sk_buff *skb)
 	struct net_device *dev;
 	unsigned int fragsize;
 	int err = -ENOENT;
+	SKB_DR(reason);
 	u8 ecn;
 
-	if (qp->q.flags & INET_FRAG_COMPLETE)
+	/* If reassembly is already done, @skb must be a duplicate frag. */
+	if (qp->q.flags & INET_FRAG_COMPLETE) {
+		SKB_DR_SET(reason, DUP_FRAG);
 		goto err;
+	}
 
 	if (!(IPCB(skb)->flags & IPSKB_FRAG_COMPLETE) &&
 	    unlikely(ip_frag_too_far(qp)) &&
@@ -382,8 +386,9 @@ static int ip_frag_queue(struct ipq *qp, struct sk_buff *skb)
 
 insert_error:
 	if (err == IPFRAG_DUP) {
-		kfree_skb(skb);
-		return -EINVAL;
+		SKB_DR_SET(reason, DUP_FRAG);
+		err = -EINVAL;
+		goto err;
 	}
 	err = -EINVAL;
 	__IP_INC_STATS(net, IPSTATS_MIB_REASM_OVERLAPS);
@@ -391,7 +396,7 @@ static int ip_frag_queue(struct ipq *qp, struct sk_buff *skb)
 	inet_frag_kill(&qp->q);
 	__IP_INC_STATS(net, IPSTATS_MIB_REASMFAILS);
 err:
-	kfree_skb(skb);
+	kfree_skb_reason(skb, reason);
 	return err;
 }
 

net/ipv6/netfilter/nf_conntrack_reasm.c

@@ -253,7 +253,7 @@ static int nf_ct_frag6_queue(struct frag_queue *fq, struct sk_buff *skb,
 	if (err) {
 		if (err == IPFRAG_DUP) {
 			/* No error for duplicates, pretend they got queued. */
-			kfree_skb(skb);
+			kfree_skb_reason(skb, SKB_DROP_REASON_DUP_FRAG);
 			return -EINPROGRESS;
 		}
 		goto insert_error;

net/ipv6/reassembly.c

@@ -112,10 +112,14 @@ static int ip6_frag_queue(struct frag_queue *fq, struct sk_buff *skb,
 	struct sk_buff *prev_tail;
 	struct net_device *dev;
 	int err = -ENOENT;
+	SKB_DR(reason);
 	u8 ecn;
 
-	if (fq->q.flags & INET_FRAG_COMPLETE)
+	/* If reassembly is already done, @skb must be a duplicate frag. */
+	if (fq->q.flags & INET_FRAG_COMPLETE) {
+		SKB_DR_SET(reason, DUP_FRAG);
 		goto err;
+	}
 
 	err = -EINVAL;
 	offset = ntohs(fhdr->frag_off) & ~0x7;
@@ -226,8 +230,9 @@ static int ip6_frag_queue(struct frag_queue *fq, struct sk_buff *skb,
 
 insert_error:
 	if (err == IPFRAG_DUP) {
-		kfree_skb(skb);
-		return -EINVAL;
+		SKB_DR_SET(reason, DUP_FRAG);
+		err = -EINVAL;
+		goto err;
 	}
 	err = -EINVAL;
 	__IP6_INC_STATS(net, ip6_dst_idev(skb_dst(skb)),
@@ -237,7 +242,7 @@ static int ip6_frag_queue(struct frag_queue *fq, struct sk_buff *skb,
 	__IP6_INC_STATS(net, ip6_dst_idev(skb_dst(skb)),
 			IPSTATS_MIB_REASMFAILS);
 err:
-	kfree_skb(skb);
+	kfree_skb_reason(skb, reason);
 	return err;
 }