[PATCH net-next v2 06/12] udp: Support gro_ipv4_max_size > 65536

[Alice Mikityanska <alice.kernel@fastmail.im>]

From: Alice Mikityanska <alice@isovalent.com>

Currently, gro_max_size and gro_ipv4_max_size can be set to values
bigger than 65536, and GRO will happily aggregate UDP to the configured
size (for example, with TCP traffic in VXLAN tunnels). However,
udp_gro_complete uses the 16-bit length field in the UDP header to store
the length of the aggregated packet. It leads to the packet truncation
later in __udp4_lib_rcv.

Fix this by storing 0 to the UDP length field and by restoring the real
length from skb->len in __udp4_lib_rcv.

Signed-off-by: Alice Mikityanska <alice@isovalent.com>
---
 net/ipv4/udp.c         | 5 ++++-
 net/ipv4/udp_offload.c | 4 ++--
 net/ipv6/udp_offload.c | 2 +-
 3 files changed, 7 insertions(+), 4 deletions(-)

diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index 345ef93001fc..870b35107ede 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -2690,7 +2690,7 @@ int __udp4_lib_rcv(struct sk_buff *skb, struct udp_table *udptable,
 {
 	struct sock *sk = NULL;
 	struct udphdr *uh;
-	unsigned short ulen;
+	unsigned int ulen;
 	struct rtable *rt = skb_rtable(skb);
 	__be32 saddr, daddr;
 	struct net *net = dev_net(skb->dev);
@@ -2714,6 +2714,9 @@ int __udp4_lib_rcv(struct sk_buff *skb, struct udp_table *udptable,
 		goto short_packet;
 
 	if (proto == IPPROTO_UDP) {
+		if (!ulen)
+			ulen = skb->len;
+
 		/* UDP validates ulen. */
 		if (ulen < sizeof(*uh) || pskb_trim_rcsum(skb, ulen))
 			goto short_packet;
diff --git a/net/ipv4/udp_offload.c b/net/ipv4/udp_offload.c
index 2f35b485ff40..780df257a8d9 100644
--- a/net/ipv4/udp_offload.c
+++ b/net/ipv4/udp_offload.c
@@ -920,7 +920,7 @@ int udp_gro_complete(struct sk_buff *skb, int nhoff,
 	struct sock *sk;
 	int err;
 
-	udp_set_len_short(uh, newlen);
+	udp_set_len(uh, newlen);
 
 	sk = INDIRECT_CALL_INET(lookup, udp6_lib_lookup_skb,
 				udp4_lib_lookup_skb, skb, uh->source, uh->dest);
@@ -958,7 +958,7 @@ INDIRECT_CALLABLE_SCOPE int udp4_gro_complete(struct sk_buff *skb, int nhoff)
 
 	/* do fraglist only if there is no outer UDP encap (or we already processed it) */
 	if (NAPI_GRO_CB(skb)->is_flist && !NAPI_GRO_CB(skb)->encap_mark) {
-		udp_set_len_short(uh, skb->len - nhoff);
+		udp_set_len(uh, skb->len - nhoff);
 
 		skb_shinfo(skb)->gso_type |= (SKB_GSO_FRAGLIST|SKB_GSO_UDP_L4);
 		skb_shinfo(skb)->gso_segs = NAPI_GRO_CB(skb)->count;
diff --git a/net/ipv6/udp_offload.c b/net/ipv6/udp_offload.c
index bfe0d7104e8a..37b90ad9f9b2 100644
--- a/net/ipv6/udp_offload.c
+++ b/net/ipv6/udp_offload.c
@@ -172,7 +172,7 @@ int udp6_gro_complete(struct sk_buff *skb, int nhoff)
 
 	/* do fraglist only if there is no outer UDP encap (or we already processed it) */
 	if (NAPI_GRO_CB(skb)->is_flist && !NAPI_GRO_CB(skb)->encap_mark) {
-		udp_set_len_short(uh, skb->len - nhoff);
+		udp_set_len(uh, skb->len - nhoff);
 
 		skb_shinfo(skb)->gso_type |= (SKB_GSO_FRAGLIST|SKB_GSO_UDP_L4);
 		skb_shinfo(skb)->gso_segs = NAPI_GRO_CB(skb)->count;
-- 
2.52.0