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[34.86.60.15]) by smtp.gmail.com with UTF8SMTPSA id 00721157ae682-798dec8b953sm11857787b3.6.2026.03.06.13.31.46 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 06 Mar 2026 13:31:46 -0800 (PST) Date: Fri, 06 Mar 2026 16:31:46 -0500 From: Willem de Bruijn To: Willem de Bruijn , Alice Mikityanska , Daniel Borkmann , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Xin Long , Willem de Bruijn , David Ahern , Nikolay Aleksandrov Cc: Shuah Khan , Stanislav Fomichev , Andrew Lunn , Simon Horman , Florian Westphal , netdev@vger.kernel.org, Alice Mikityanska Message-ID: In-Reply-To: References: <20260226201600.222044-1-alice.kernel@fastmail.im> <20260226201600.222044-7-alice.kernel@fastmail.im> Subject: Re: [PATCH net-next v2 06/12] udp: Support gro_ipv4_max_size > 65536 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Willem de Bruijn wrote: > Alice Mikityanska wrote: > > From: Alice Mikityanska > > > > 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 > > --- > > 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; > > + > > For normal packets, ip_rcv_core truncates skbs to their IP length. > > I don't immediate see the GRO layer taking care of this. Which is fine > if it can be done later, but not if these protocol fields are zeroed. > > Should we validate that packets have no padding before we coalesce? I should have read ahead. This is addressed in patch 8. Great! Never mind this comment.