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Message-ID: <20240824191819.GU2164@kernel.org>
Date: Sat, 24 Aug 2024 20:18:19 +0100
From: Simon Horman <horms@...nel.org>
To: Tom Herbert <tom@...bertland.com>
Cc: davem@...emloft.net, kuba@...nel.org, edumazet@...gle.com,
netdev@...r.kernel.org, felipe@...anda.io,
willemdebruijn.kernel@...il.com, pablo@...filter.org,
laforge@...monks.org, xeb@...l.ru
Subject: Re: [PATCH net-next v4 05/13] flow_dissector: UDP encap
infrastructure
On Fri, Aug 23, 2024 at 01:15:49PM -0700, Tom Herbert wrote:
> Add infrastructure for parsing into UDP encapsulations
>
> Add function __skb_flow_dissect_udp that is called for IPPROTO_UDP.
> The flag FLOW_DISSECTOR_F_PARSE_UDP_ENCAPS enables parsing of UDP
> encapsulations. If the flag is set when parsing a UDP packet then
> a socket lookup is performed. The offset of the base network header,
> either an IPv4 or IPv6 header, is tracked and passed to
> __skb_flow_dissect_udp so that it can perform the socket lookup
>
> If a socket is found and it's for a UDP encapsulation (encap_type is
> set in the UDP socket) then a switch is performed on the encap_type
> value (cases are UDP_ENCAP_* values)
>
> An encapsulated packet in UDP can either be indicated by an
> EtherType or IP protocol. The processing for dissecting a UDP encap
> protocol returns a flow dissector return code. If
> FLOW_DISSECT_RET_PROTO_AGAIN or FLOW_DISSECT_RET_IPPROTO_AGAIN is
> returned then the corresponding encapsulated protocol is dissected.
> The nhoff is set to point to the header to process. In the case
> FLOW_DISSECT_RET_PROTO_AGAIN the EtherType protocol is returned and
> the IP protocol is set to zero. In the case of
> FLOW_DISSECT_RET_IPPROTO_AGAIN, the IP protocol is returned and
> the EtherType protocol is returned unchanged
>
> Signed-off-by: Tom Herbert <tom@...bertland.com>
...
> diff --git a/net/core/flow_dissector.c b/net/core/flow_dissector.c
...
> @@ -806,6 +807,134 @@ __skb_flow_dissect_batadv(const struct sk_buff *skb,
> return FLOW_DISSECT_RET_PROTO_AGAIN;
> }
>
> +static enum flow_dissect_ret
> +__skb_flow_dissect_udp(const struct sk_buff *skb, const struct net *net,
> + struct flow_dissector *flow_dissector,
> + void *target_container, const void *data,
> + int *p_nhoff, int hlen, __be16 *p_proto,
> + u8 *p_ip_proto, int base_nhoff, unsigned int flags,
> + unsigned int num_hdrs)
> +{
> + enum flow_dissect_ret ret;
> + struct udphdr _udph;
> + int nhoff;
> +
> + if (!(flags & FLOW_DISSECTOR_F_PARSE_UDP_ENCAPS))
> + return FLOW_DISSECT_RET_OUT_GOOD;
> +
> + /* Check that the netns for the skb device is the same as the caller's,
> + * and only dissect UDP if we haven't yet encountered any encapsulation.
> + * The goal is to ensure that the socket lookup is being done in the
> + * right netns. Encapsulations may push packets into different name
> + * spaces, so this scheme is restricting UDP dissection to cases where
> + * they are in the same name spaces or at least the original name space.
> + * This should capture the majority of use cases for UDP encaps, and
> + * if we do encounter a UDP encapsulation within a different namespace
> + * then the only effect is we don't attempt UDP dissection
> + */
> + if (dev_net(skb->dev) != net || num_hdrs > 0)
> + return FLOW_DISSECT_RET_OUT_GOOD;
> +
> + switch (*p_proto) {
> +#ifdef CONFIG_INET
> + case htons(ETH_P_IP): {
> + const struct udphdr *udph;
> + const struct iphdr *iph;
> + struct iphdr _iph;
> + struct sock *sk;
> +
> + iph = __skb_header_pointer(skb, base_nhoff, sizeof(_iph), data,
> + hlen, &_iph);
> + if (!iph)
> + return FLOW_DISSECT_RET_OUT_BAD;
> +
> + udph = __skb_header_pointer(skb, *p_nhoff, sizeof(_udph), data,
> + hlen, &_udph);
> + if (!udph)
> + return FLOW_DISSECT_RET_OUT_BAD;
> +
> + rcu_read_lock();
> + /* Look up the UDPv4 socket and get the encap_type */
> + sk = __udp4_lib_lookup(net, iph->saddr, udph->source,
> + iph->daddr, udph->dest,
> + inet_iif(skb), inet_sdif(skb),
> + net->ipv4.udp_table, NULL);
> + if (!sk || !udp_sk(sk)->encap_type) {
> + rcu_read_unlock();
> + return FLOW_DISSECT_RET_OUT_GOOD;
> + }
> +
> + encap_type = udp_sk(sk)->encap_type;
Hi Tom,
I guess a local change went astray, or something like that,
because encap_type isn't declared in this scope.
> + rcu_read_unlock();
> +
> + break;
> + }
...
--
pw-bot: cr
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