[PATCH net-next v8 4/9] udp: Support gro_ipv4_max_size > 65536
From: Alice Mikityanska <hidden>
Date: 2026-07-06 18:20:56
Subsystem:
networking [general], the rest, user datagram protocol (udp) · Maintainers:
"David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Linus Torvalds, Willem de Bruijn
From: Alice Mikityanska <redacted> 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 udp_rcv. Fix this by storing 0 to the UDP length field and by restoring the real length from skb->len in udp_rcv. IP GRO already can store 0 to the IP length field, and iph_totlen()/ipv6_payload_len() are capable of restoring the real length, because the relevant packets (BIG TCP tunneled in UDP tunnels) will have skb_is_gso_tcp == true. Additionally, restrict handling uh->len=0 in udpv6_rcv to BIG TCP and jumbograms only by using the udp_get_len helper. Signed-off-by: Alice Mikityanska <redacted> Reviewed-by: Willem de Bruijn <willemb@google.com> --- net/ipv4/udp.c | 4 ++-- net/ipv4/udp_offload.c | 4 ++-- net/ipv6/udp.c | 4 ++-- net/ipv6/udp_offload.c | 2 +- 4 files changed, 7 insertions(+), 7 deletions(-)
diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index cb86124fd963..2b9b55a14758 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c@@ -2592,8 +2592,8 @@ 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;
@@ -2607,7 +2607,7 @@ int udp_rcv(struct sk_buff *skb) goto drop; /* No space for header. */ uh = udp_hdr(skb); - ulen = ntohs(uh->len); + ulen = udp_get_len(skb, uh, 0); saddr = ip_hdr(skb)->saddr; daddr = ip_hdr(skb)->daddr;
diff --git a/net/ipv4/udp_offload.c b/net/ipv4/udp_offload.c
index 493e2b9e16fb..4f9a3922937c 100644
--- a/net/ipv4/udp_offload.c
+++ b/net/ipv4/udp_offload.c@@ -919,7 +919,7 @@ 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);
@@ -956,7 +956,7 @@ 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.c b/net/ipv6/udp.c
index 8bbd55546b6e..02272466f4c2 100644
--- a/net/ipv6/udp.c
+++ b/net/ipv6/udp.c@@ -1081,12 +1081,12 @@ INDIRECT_CALLABLE_SCOPE int udpv6_rcv(struct sk_buff *skb) daddr = &ipv6_hdr(skb)->daddr; uh = udp_hdr(skb); - ulen = ntohs(uh->len); + ulen = udp_get_len(skb, uh, 0); if (ulen > skb->len) goto short_packet; /* Check for jumbo payload */ - if (ulen == 0) + if (ulen == 0 && inet6_is_jumbogram(skb)) ulen = skb->len; if (ulen < sizeof(*uh))
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