netdev - Re: [PATCH 12/12] flow_dissector: Parse gtp in UDP

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Message-ID: <66ae85424c858_2a823d29427@willemb.c.googlers.com.notmuch>
Date: Sat, 03 Aug 2024 15:30:10 -0400
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
To: Tom Herbert <tom@...bertland.com>, 
 davem@...emloft.net, 
 kuba@...nel.org, 
 edumazet@...gle.com, 
 netdev@...r.kernel.org, 
 felipe@...anda.io
Cc: Tom Herbert <tom@...bertland.com>
Subject: Re: [PATCH 12/12] flow_dissector: Parse gtp in UDP

Tom Herbert wrote:
> Parse both version 0 and 1. Call __skb_direct_ip_dissect to determine
> IP version of the encapsulated packet
> 
> Signed-off-by: Tom Herbert <tom@...bertland.com>
> ---
>  net/core/flow_dissector.c | 87 +++++++++++++++++++++++++++++++++++++++
>  1 file changed, 87 insertions(+)
> 
> diff --git a/net/core/flow_dissector.c b/net/core/flow_dissector.c
> index 7f0bf737c3db..af197ed560b8 100644
> --- a/net/core/flow_dissector.c
> +++ b/net/core/flow_dissector.c
> @@ -9,6 +9,7 @@
>  #include <net/dsa.h>
>  #include <net/dst_metadata.h>
>  #include <net/fou.h>
> +#include <net/gtp.h>
>  #include <net/ip.h>
>  #include <net/ipv6.h>
>  #include <net/geneve.h>
> @@ -35,6 +36,7 @@
>  #include <net/pkt_cls.h>
>  #include <scsi/fc/fc_fcoe.h>
>  #include <uapi/linux/batadv_packet.h>
> +#include <uapi/linux/gtp.h>
>  #include <linux/bpf.h>
>  #if IS_ENABLED(CONFIG_NF_CONNTRACK)
>  #include <net/netfilter/nf_conntrack_core.h>
> @@ -887,6 +889,81 @@ __skb_flow_dissect_gue(const struct sk_buff *skb,
>  	return FLOW_DISSECT_RET_IPPROTO_AGAIN;
>  }
>  
> +static enum flow_dissect_ret
> +__skb_flow_dissect_gtp0(const struct sk_buff *skb,
> +			struct flow_dissector *flow_dissector,
> +			void *target_container, const void *data,
> +			__u8 *p_ip_proto, int *p_nhoff, int hlen,
> +			unsigned int flags)
> +{
> +	__u8 *ip_version, _ip_version, proto;
> +	struct gtp0_header *hdr, _hdr;
> +
> +	hdr = __skb_header_pointer(skb, *p_nhoff, sizeof(_hdr), data, hlen,
> +				   &_hdr);
> +	if (!hdr)
> +		return FLOW_DISSECT_RET_OUT_BAD;
> +
> +	if ((hdr->flags >> 5) != GTP_V0)
> +		return FLOW_DISSECT_RET_OUT_GOOD;
> +
> +	ip_version = skb_header_pointer(skb, *p_nhoff + sizeof(_hdr),
> +					sizeof(*ip_version),
> +					&_ip_version);
> +	if (!ip_version)
> +		return FLOW_DISSECT_RET_OUT_BAD;
> +
> +	proto = __skb_direct_ip_dissect(ip_version);
> +	if (!proto)
> +		return FLOW_DISSECT_RET_OUT_GOOD;
> +
> +	*p_ip_proto = proto;
> +	*p_nhoff += sizeof(struct gtp0_header);
> +
> +	return FLOW_DISSECT_RET_IPPROTO_AGAIN;
> +}
> +
> +static enum flow_dissect_ret
> +__skb_flow_dissect_gtp1u(const struct sk_buff *skb,
> +			 struct flow_dissector *flow_dissector,
> +			 void *target_container, const void *data,
> +			 __u8 *p_ip_proto, int *p_nhoff, int hlen,
> +			 unsigned int flags)
> +{
> +	__u8 *ip_version, _ip_version, proto;
> +	struct gtp1_header *hdr, _hdr;
> +	int hdrlen = sizeof(_hdr);
> +
> +	hdr = __skb_header_pointer(skb, *p_nhoff, sizeof(_hdr), data, hlen,
> +				   &_hdr);
> +	if (!hdr)
> +		return FLOW_DISSECT_RET_OUT_BAD;
> +
> +	if ((hdr->flags >> 5) != GTP_V1)
> +		return FLOW_DISSECT_RET_OUT_GOOD;
> +
> +	if (hdr->type != GTP_TPDU)
> +		return FLOW_DISSECT_RET_OUT_GOOD;
> +
> +	if (hdr->flags & GTP1_F_MASK)
> +		hdrlen += 4;
> +

The only difference with +__skb_flow_dissect_gtp0 is these two
branches. Can probably deduplicate.

Also, escape early if any of the other optional field bits are set?

  #define GTP1_F_NPDU     0x01
  #define GTP1_F_SEQ      0x02
  #define GTP1_F_EXTHDR   0x04