[PATCH net-next v4 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>
Reviewed-by: Willem de Bruijn <willemb@google.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 3e92575f1d55..856c23b9d6dd 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -2583,8 +2583,8 @@ int udp_rcv(struct sk_buff *skb)
 	struct rtable *rt = skb_rtable(skb);
 	struct net *net = dev_net(skb->dev);
 	struct sock *sk = NULL;
-	unsigned short ulen;
 	__be32 saddr, daddr;
+	unsigned int ulen;
 	struct udphdr *uh;
 	bool refcounted;
 	int drop_reason;
@@ -2605,6 +2605,9 @@ int udp_rcv(struct sk_buff *skb)
 	if (ulen > skb->len)
 		goto short_packet;
 
+	if (!ulen)
+		ulen = skb->len;
+
 	if (ulen < sizeof(*uh))
 		goto short_packet;
 
diff --git a/net/ipv4/udp_offload.c b/net/ipv4/udp_offload.c
index 22acc80b12a4..23653872ca65 100644
--- a/net/ipv4/udp_offload.c
+++ b/net/ipv4/udp_offload.c
@@ -916,7 +916,7 @@ 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);
@@ -953,7 +953,7 @@ 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 c92cf5ee3e6a..7370bcb80332 100644
--- a/net/ipv6/udp_offload.c
+++ b/net/ipv6/udp_offload.c
@@ -171,7 +171,7 @@ 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;
-- 
2.54.0