[PATCH bpf-next v3 6/6] selftests/bpf: tc_tunnel validate decap GSO state

[Nick Hudson]

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@xxxxxxxxxx>
---
 .../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)
+
+#define SKB_GSO_TUNNEL_MASK		(SKB_GSO_UDP_TUNNEL_MASK |		\
+				 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