udp: expand SKB_DROP_REASON_UDP_CSUM use

SKB_DROP_REASON_UDP_CSUM can be used in four locations
when dropping a packet because of a wrong UDP checksum.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Link: https://patch.msgid.link/20250307102002.2095238-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/ipv4/udp.c

@@ -1848,7 +1848,7 @@ static struct sk_buff *__first_packet_length(struct sock *sk,
 			atomic_inc(&sk->sk_drops);
 			__skb_unlink(skb, rcvq);
 			*total += skb->truesize;
-			kfree_skb(skb);
+			kfree_skb_reason(skb, SKB_DROP_REASON_UDP_CSUM);
 		} else {
 			udp_skb_csum_unnecessary_set(skb);
 			break;
@@ -2002,7 +2002,7 @@ int udp_read_skb(struct sock *sk, skb_read_actor_t recv_actor)
 		__UDP_INC_STATS(net, UDP_MIB_CSUMERRORS, is_udplite);
 		__UDP_INC_STATS(net, UDP_MIB_INERRORS, is_udplite);
 		atomic_inc(&sk->sk_drops);
-		kfree_skb(skb);
+		kfree_skb_reason(skb, SKB_DROP_REASON_UDP_CSUM);
 		goto try_again;
 	}
 
@@ -2117,7 +2117,7 @@ int udp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len, int flags,
 		UDP_INC_STATS(sock_net(sk), UDP_MIB_CSUMERRORS, is_udplite);
 		UDP_INC_STATS(sock_net(sk), UDP_MIB_INERRORS, is_udplite);
 	}
-	kfree_skb(skb);
+	kfree_skb_reason(skb, SKB_DROP_REASON_UDP_CSUM);
 
 	/* starting over for a new packet, but check if we need to yield */
 	cond_resched();

net/ipv6/udp.c

@@ -586,7 +586,7 @@ int udpv6_recvmsg(struct sock *sk, struct msghdr *msg, size_t len,
 		SNMP_INC_STATS(mib, UDP_MIB_CSUMERRORS);
 		SNMP_INC_STATS(mib, UDP_MIB_INERRORS);
 	}
-	kfree_skb(skb);
+	kfree_skb_reason(skb, SKB_DROP_REASON_UDP_CSUM);
 
 	/* starting over for a new packet, but check if we need to yield */
 	cond_resched();