1 files changed, 106 insertions, 0 deletions
diff --git a/tools/testing/selftests/bpf/progs/test_tc_change_tail.c b/tools/testing/selftests/bpf/progs/test_tc_change_tail.c
new file mode 100644
index 000000000000..28edafe803f0
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/test_tc_change_tail.c
@@ -0,0 +1,106 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+#include <linux/if_ether.h>
+#include <linux/in.h>
+#include <linux/ip.h>
+#include <linux/udp.h>
+#include <linux/pkt_cls.h>
+
+long change_tail_ret = 1;
+
+static __always_inline struct iphdr *parse_ip_header(struct __sk_buff *skb, int *ip_proto)
+{
+	void *data_end = (void *)(long)skb->data_end;
+	void *data = (void *)(long)skb->data;
+	struct ethhdr *eth = data;
+	struct iphdr *iph;
+
+	/* Verify Ethernet header */
+	if ((void *)(data + sizeof(*eth)) > data_end)
+		return NULL;
+
+	/* Skip Ethernet header to get to IP header */
+	iph = (void *)(data + sizeof(struct ethhdr));
+
+	/* Verify IP header */
+	if ((void *)(data + sizeof(struct ethhdr) + sizeof(*iph)) > data_end)
+		return NULL;
+
+	/* Basic IP header validation */
+	if (iph->version != 4)  /* Only support IPv4 */
+		return NULL;
+
+	if (iph->ihl < 5)  /* Minimum IP header length */
+		return NULL;
+
+	*ip_proto = iph->protocol;
+	return iph;
+}
+
+static __always_inline struct udphdr *parse_udp_header(struct __sk_buff *skb, struct iphdr *iph)
+{
+	void *data_end = (void *)(long)skb->data_end;
+	void *hdr = (void *)iph;
+	struct udphdr *udp;
+
+	/* Calculate UDP header position */
+	udp = hdr + (iph->ihl * 4);
+	hdr = (void *)udp;
+
+	/* Verify UDP header bounds */
+	if ((void *)(hdr + sizeof(*udp)) > data_end)
+		return NULL;
+
+	return udp;
+}
+
+SEC("tc/ingress")
+int change_tail(struct __sk_buff *skb)
+{
+	int len = skb->len;
+	struct udphdr *udp;
+	struct iphdr *iph;
+	void *data_end;
+	char *payload;
+	int ip_proto;
+
+	bpf_skb_pull_data(skb, len);
+
+	data_end = (void *)(long)skb->data_end;
+	iph = parse_ip_header(skb, &ip_proto);
+	if (!iph)
+		return TCX_PASS;
+
+	if (ip_proto != IPPROTO_UDP)
+		return TCX_PASS;
+
+	udp = parse_udp_header(skb, iph);
+	if (!udp)
+		return TCX_PASS;
+
+	payload = (char *)udp + (sizeof(struct udphdr));
+	if (payload + 1 > (char *)data_end)
+		return TCX_PASS;
+
+	if (payload[0] == 'T') { /* Trim the packet */
+		change_tail_ret = bpf_skb_change_tail(skb, len - 1, 0);
+		if (!change_tail_ret)
+			bpf_skb_change_tail(skb, len, 0);
+		return TCX_PASS;
+	} else if (payload[0] == 'G') { /* Grow the packet */
+		change_tail_ret = bpf_skb_change_tail(skb, len + 1, 0);
+		if (!change_tail_ret)
+			bpf_skb_change_tail(skb, len, 0);
+		return TCX_PASS;
+	} else if (payload[0] == 'E') { /* Error */
+		change_tail_ret = bpf_skb_change_tail(skb, 65535, 0);
+		return TCX_PASS;
+	} else if (payload[0] == 'Z') { /* Zero */
+		change_tail_ret = bpf_skb_change_tail(skb, 0, 0);
+		return TCX_PASS;
+	}
+	return TCX_DROP;
+}
+
+char _license[] SEC("license") = "GPL";