net: udp: fix IP header access and skb lookup on Fast/frag0 UDP GRO

udp{4,6}_lib_lookup_skb() use ip{,v6}_hdr() to get IP header of the
packet. While it's probably OK for non-frag0 paths, this helpers
will also point to junk on Fast/frag0 GRO when all headers are
located in frags. As a result, sk/skb lookup may fail or give wrong
results. To support both GRO modes, skb_gro_network_header() might
be used. To not modify original functions, add private versions of
udp{4,6}_lib_lookup_skb() only to perform correct sk lookups on GRO.

Present since the introduction of "application-level" UDP GRO
in 4.7-rc1.

Misc: replace totally unneeded ternaries with plain ifs.

Fixes: a6024562 ("udp: Add GRO functions to UDP socket")
Suggested-by: Willem de Bruijn <willemb@google.com>
Cc: Eric Dumazet <edumazet@google.com>
Signed-off-by: Alexander Lobakin <alobakin@pm.me>
Acked-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/ipv4/udp_offload.c

@@ -500,12 +500,22 @@ struct sk_buff *udp_gro_receive(struct list_head *head, struct sk_buff *skb,
 }
 EXPORT_SYMBOL(udp_gro_receive);
 
+static struct sock *udp4_gro_lookup_skb(struct sk_buff *skb, __be16 sport,
+					__be16 dport)
+{
+	const struct iphdr *iph = skb_gro_network_header(skb);
+
+	return __udp4_lib_lookup(dev_net(skb->dev), iph->saddr, sport,
+				 iph->daddr, dport, inet_iif(skb),
+				 inet_sdif(skb), &udp_table, NULL);
+}
+
 INDIRECT_CALLABLE_SCOPE
 struct sk_buff *udp4_gro_receive(struct list_head *head, struct sk_buff *skb)
 {
 	struct udphdr *uh = udp_gro_udphdr(skb);
+	struct sock *sk = NULL;
 	struct sk_buff *pp;
-	struct sock *sk;
 
 	if (unlikely(!uh))
 		goto flush;
@@ -523,7 +533,10 @@ struct sk_buff *udp4_gro_receive(struct list_head *head, struct sk_buff *skb)
 skip:
 	NAPI_GRO_CB(skb)->is_ipv6 = 0;
 	rcu_read_lock();
-	sk = static_branch_unlikely(&udp_encap_needed_key) ? udp4_lib_lookup_skb(skb, uh->source, uh->dest) : NULL;
+
+	if (static_branch_unlikely(&udp_encap_needed_key))
+		sk = udp4_gro_lookup_skb(skb, uh->source, uh->dest);
+
 	pp = udp_gro_receive(head, skb, uh, sk);
 	rcu_read_unlock();
 	return pp;

net/ipv6/udp_offload.c

@@ -111,12 +111,22 @@ static struct sk_buff *udp6_ufo_fragment(struct sk_buff *skb,
 	return segs;
 }
 
+static struct sock *udp6_gro_lookup_skb(struct sk_buff *skb, __be16 sport,
+					__be16 dport)
+{
+	const struct ipv6hdr *iph = skb_gro_network_header(skb);
+
+	return __udp6_lib_lookup(dev_net(skb->dev), &iph->saddr, sport,
+				 &iph->daddr, dport, inet6_iif(skb),
+				 inet6_sdif(skb), &udp_table, NULL);
+}
+
 INDIRECT_CALLABLE_SCOPE
 struct sk_buff *udp6_gro_receive(struct list_head *head, struct sk_buff *skb)
 {
 	struct udphdr *uh = udp_gro_udphdr(skb);
+	struct sock *sk = NULL;
 	struct sk_buff *pp;
-	struct sock *sk;
 
 	if (unlikely(!uh))
 		goto flush;
@@ -135,7 +145,10 @@ struct sk_buff *udp6_gro_receive(struct list_head *head, struct sk_buff *skb)
 skip:
 	NAPI_GRO_CB(skb)->is_ipv6 = 1;
 	rcu_read_lock();
-	sk = static_branch_unlikely(&udpv6_encap_needed_key) ? udp6_lib_lookup_skb(skb, uh->source, uh->dest) : NULL;
+
+	if (static_branch_unlikely(&udpv6_encap_needed_key))
+		sk = udp6_gro_lookup_skb(skb, uh->source, uh->dest);
+
 	pp = udp_gro_receive(head, skb, uh, sk);
 	rcu_read_unlock();
 	return pp;