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([2a0d:3344:2712:7e10:4d59:d956:544f:d65c]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-40fb9c32734sm3308186f8f.25.2025.09.25.07.10.06 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 25 Sep 2025 07:10:06 -0700 (PDT) Message-ID: Date: Thu, 25 Sep 2025 16:10:05 +0200 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH net-next 14/17] udp: Validate UDP length in udp_gro_receive To: Maxim Mikityanskiy , Daniel Borkmann , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Willem de Bruijn , David Ahern , Nikolay Aleksandrov Cc: netdev@vger.kernel.org, tcpdump-workers@lists.tcpdump.org, Guy Harris , Michael Richardson , Denis Ovsienko , Xin Long , Maxim Mikityanskiy References: <20250923134742.1399800-1-maxtram95@gmail.com> <20250923134742.1399800-15-maxtram95@gmail.com> Content-Language: en-US From: Paolo Abeni In-Reply-To: <20250923134742.1399800-15-maxtram95@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 9/23/25 3:47 PM, Maxim Mikityanskiy wrote: > From: Maxim Mikityanskiy > > From: Maxim Mikityanskiy > > In the previous commit we started using uh->len = 0 as a marker of a GRO > packet bigger than 65536 bytes. To prevent abuse by maliciously crafted > packets, check the length in the UDP header in udp_gro_receive. Note > that a similar check is present in udp_gro_receive_segment, but not in > the UDP socket gro_receive flow. > > Signed-off-by: Maxim Mikityanskiy > --- > net/ipv4/udp_offload.c | 5 +++++ > 1 file changed, 5 insertions(+) > > diff --git a/net/ipv4/udp_offload.c b/net/ipv4/udp_offload.c > index 1e7ed7718d7b..fd86f76fda2c 100644 > --- a/net/ipv4/udp_offload.c > +++ b/net/ipv4/udp_offload.c > @@ -788,6 +788,7 @@ struct sk_buff *udp_gro_receive(struct list_head *head, struct sk_buff *skb, > struct sk_buff *p; > struct udphdr *uh2; > unsigned int off = skb_gro_offset(skb); > + unsigned int ulen; > int flush = 1; > > /* We can do L4 aggregation only if the packet can't land in a tunnel > @@ -820,6 +821,10 @@ struct sk_buff *udp_gro_receive(struct list_head *head, struct sk_buff *skb, > !NAPI_GRO_CB(skb)->csum_valid)) > goto out; > > + ulen = ntohs(uh->len); > + if (ulen <= sizeof(*uh) || ulen != skb_gro_len(skb)) > + goto out; Possibly consolidate both checks in single, earlier one? /P