udp: never accept GSO_FRAGLIST packets

Currently the UDP protocol delivers GSO_FRAGLIST packets to
the sockets without the expected segmentation.

This change addresses the issue introducing and maintaining
a couple of new fields to explicitly accept SKB_GSO_UDP_L4
or GSO_FRAGLIST packets. Additionally updates udp_unexpected_gso()
accordingly.

UDP sockets enabling UDP_GRO stil keep accept_udp_fraglist
zeroed.

v1 -> v2:
- use 2 bits instead of a whole GSO bitmask (Willem)

Fixes: 9fd1ff5d2ac7 ("udp: Support UDP fraglist GRO/GSO.")
Signed-off-by: Paolo Abeni <[e-mail]>
Reviewed-by: Willem de Bruijn <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

include/linux/udp.h

···
 					   * different encapsulation layer set
 					   * this
 					   */
-			 gro_enabled:1;	/* Can accept GRO packets */
+			 gro_enabled:1,	/* Request GRO aggregation */
+			 accept_udp_l4:1,
+			 accept_udp_fraglist:1;
 	/*
 	 * Following member retains the information to create a UDP header
 	 * when the socket is uncorked.
···
 
 static inline bool udp_unexpected_gso(struct sock *sk, struct sk_buff *skb)
 {
-	return !udp_sk(sk)->gro_enabled && skb_is_gso(skb) &&
-	       skb_shinfo(skb)->gso_type & SKB_GSO_UDP_L4;
+	if (!skb_is_gso(skb))
+		return false;
+
+	if (skb_shinfo(skb)->gso_type & SKB_GSO_UDP_L4 && !udp_sk(sk)->accept_udp_l4)
+		return true;
+
+	if (skb_shinfo(skb)->gso_type & SKB_GSO_FRAGLIST && !udp_sk(sk)->accept_udp_fraglist)
+		return true;
+
+	return false;
 }
 
 #define udp_portaddr_for_each_entry(__sk, list) \

net/ipv4/udp.c

···
 
 	case UDP_GRO:
 		lock_sock(sk);
+
+		/* when enabling GRO, accept the related GSO packet type */
 		if (valbool)
 			udp_tunnel_encap_enable(sk->sk_socket);
 		up->gro_enabled = valbool;
+		up->accept_udp_l4 = valbool;
 		release_sock(sk);
 		break;