Re: [PATCH bpf-next v4 6/6] selftests/bpf: tc_tunnel validate decap GSO state

[Willem de Bruijn <willemdebruijn.kernel@gmail.com>]

Nick Hudson wrote:
> Require BPF_F_ADJ_ROOM_DECAP_L4_UDP and BPF_F_ADJ_ROOM_DECAP_L4_GRE enum
> values at runtime using CO-RE enum existence checks so missing kernel
> support fails fast instead of silently proceeding.
> 
> After bpf_skb_adjust_room() decapsulation, inspect skb_shared_info and
> sk_buff state for GSO packets and assert that the expected tunnel GSO
> bits are cleared and encapsulation matches the remaining tunnel state.
> 
> Signed-off-by: Nick Hudson <nhudson@akamai.com>
> ---
>  .../selftests/bpf/progs/test_tc_tunnel.c      | 58 +++++++++++++++++++
>  1 file changed, 58 insertions(+)
> 
> diff --git a/tools/testing/selftests/bpf/progs/test_tc_tunnel.c b/tools/testing/selftests/bpf/progs/test_tc_tunnel.c
> index 7376df405a6b..74dfb694a210 100644
> --- a/tools/testing/selftests/bpf/progs/test_tc_tunnel.c
> +++ b/tools/testing/selftests/bpf/progs/test_tc_tunnel.c
> @@ -6,6 +6,7 @@
>  
>  #include <bpf/bpf_helpers.h>
>  #include <bpf/bpf_endian.h>
> +#include <bpf/bpf_core_read.h>
>  #include "bpf_tracing_net.h"
>  #include "bpf_compiler.h"
>  
> @@ -37,6 +38,23 @@ struct vxlanhdr___local {
>  
>  #define	EXTPROTO_VXLAN	0x1
>  
> +#define SKB_GSO_UDP_TUNNEL_MASK	(SKB_GSO_UDP_TUNNEL |			\
> +				 SKB_GSO_UDP_TUNNEL_CSUM |		\
> +				 SKB_GSO_TUNNEL_REMCSUM)

Leftover remcsum reference?

> +
> +#define SKB_GSO_TUNNEL_MASK		(SKB_GSO_UDP_TUNNEL_MASK |		\

Odd indentation?

> +				 SKB_GSO_GRE |				\
> +				 SKB_GSO_GRE_CSUM |			\
> +				 SKB_GSO_IPXIP4 |			\
> +				 SKB_GSO_IPXIP6 |			\
> +				 SKB_GSO_ESP)
> +
> +#define BPF_F_ADJ_ROOM_DECAP_L4_MASK	(BPF_F_ADJ_ROOM_DECAP_L4_UDP |	\
> +				 BPF_F_ADJ_ROOM_DECAP_L4_GRE)
> +
> +#define BPF_F_ADJ_ROOM_DECAP_IPXIP_MASK	(BPF_F_ADJ_ROOM_DECAP_IPXIP4 |	\
> +					 BPF_F_ADJ_ROOM_DECAP_IPXIP6)
> +
>  #define	VXLAN_FLAGS     bpf_htonl(1<<27)
>  #define	VNI_ID		1
>  #define	VXLAN_VNI	bpf_htonl(VNI_ID << 8)
> @@ -592,6 +610,8 @@ int __encap_ip6vxlan_eth(struct __sk_buff *skb)
>  static int decap_internal(struct __sk_buff *skb, int off, int len, char proto)
>  {
>  	__u64 flags = BPF_F_ADJ_ROOM_FIXED_GSO;
> +	struct sk_buff *kskb;
> +	struct skb_shared_info *shinfo;
>  	struct ipv6_opt_hdr ip6_opt_hdr;
>  	struct gre_hdr greh;
>  	struct udphdr udph;
> @@ -621,6 +641,11 @@ static int decap_internal(struct __sk_buff *skb, int off, int len, char proto)
>  		break;
>  	case IPPROTO_GRE:
>  		olen += sizeof(struct gre_hdr);
> +		if (!bpf_core_enum_value_exists(enum bpf_adj_room_flags,
> +						BPF_F_ADJ_ROOM_DECAP_L4_GRE))
> +			return TC_ACT_SHOT;
> +		flags |= BPF_F_ADJ_ROOM_DECAP_L4_GRE;
> +
>  		if (bpf_skb_load_bytes(skb, off + len, &greh, sizeof(greh)) < 0)
>  			return TC_ACT_OK;
>  		switch (bpf_ntohs(greh.protocol)) {
> @@ -634,6 +659,10 @@ static int decap_internal(struct __sk_buff *skb, int off, int len, char proto)
>  		break;
>  	case IPPROTO_UDP:
>  		olen += sizeof(struct udphdr);
> +		if (!bpf_core_enum_value_exists(enum bpf_adj_room_flags,
> +						BPF_F_ADJ_ROOM_DECAP_L4_UDP))
> +			return TC_ACT_SHOT;
> +		flags |= BPF_F_ADJ_ROOM_DECAP_L4_UDP;
>  		if (bpf_skb_load_bytes(skb, off + len, &udph, sizeof(udph)) < 0)
>  			return TC_ACT_OK;
>  		switch (bpf_ntohs(udph.dest)) {
> @@ -655,6 +684,35 @@ static int decap_internal(struct __sk_buff *skb, int off, int len, char proto)
>  	if (bpf_skb_adjust_room(skb, -olen, BPF_ADJ_ROOM_MAC, flags))
>  		return TC_ACT_SHOT;
>  
> +	kskb = bpf_cast_to_kern_ctx(skb);
> +	shinfo = bpf_core_cast(kskb->head + kskb->end, struct skb_shared_info);
> +	if (!shinfo->gso_size)
> +		return TC_ACT_OK;
> +
> +	if ((flags & BPF_F_ADJ_ROOM_DECAP_L4_UDP) &&
> +	    (shinfo->gso_type & SKB_GSO_UDP_TUNNEL_MASK))
> +		return TC_ACT_SHOT;
> +
> +	if ((flags & BPF_F_ADJ_ROOM_DECAP_L4_GRE) &&
> +	    (shinfo->gso_type & (SKB_GSO_GRE | SKB_GSO_GRE_CSUM)))
> +		return TC_ACT_SHOT;
> +
> +	if ((flags & BPF_F_ADJ_ROOM_DECAP_IPXIP4) &&
> +	    (shinfo->gso_type & SKB_GSO_IPXIP4))
> +		return TC_ACT_SHOT;
> +
> +	if ((flags & BPF_F_ADJ_ROOM_DECAP_IPXIP6) &&
> +	    (shinfo->gso_type & SKB_GSO_IPXIP6))
> +		return TC_ACT_SHOT;
> +
> +	if (flags & (BPF_F_ADJ_ROOM_DECAP_L4_MASK |
> +		     BPF_F_ADJ_ROOM_DECAP_IPXIP_MASK)) {
> +		if ((shinfo->gso_type & SKB_GSO_TUNNEL_MASK) && !kskb->encapsulation)
> +			return TC_ACT_SHOT;
> +		if (!(shinfo->gso_type & SKB_GSO_TUNNEL_MASK) && kskb->encapsulation)
> +			return TC_ACT_SHOT;
> +	}
> +
>  	return TC_ACT_OK;
>  }
>  
> -- 
> 2.34.1
>