Commit 4a58963d authored by Cong Wang's avatar Cong Wang Committed by Daniel Borkmann
Browse files

selftests/bpf: Test bpf_skb_change_tail() in TC ingress 



Similarly to the previous test, we also need a test case to cover
positive offsets as well, TC is an excellent hook for this.

Signed-off-by: default avatarCong Wang <cong.wang@bytedance.com>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Tested-by: default avatarZijian Zhang <zijianzhang@bytedance.com>
Acked-by: default avatarJohn Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/bpf/20241213034057.246437-5-xiyou.wangcong@gmail.com
parent 472759c9

tools/testing/selftests/bpf/prog_tests/tc_change_tail.c

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// SPDX-License-Identifier: GPL-2.0

#include <error.h>

#include <test_progs.h>

#include <linux/pkt_cls.h>



#include "test_tc_change_tail.skel.h"

#include "socket_helpers.h"



#define LO_IFINDEX 1



void test_tc_change_tail(void)

{

	LIBBPF_OPTS(bpf_tcx_opts, tcx_opts);

	struct test_tc_change_tail *skel = NULL;

	struct bpf_link *link;

	int c1, p1;

	char buf[2];

	int ret;



	skel = test_tc_change_tail__open_and_load();

	if (!ASSERT_OK_PTR(skel, "test_tc_change_tail__open_and_load"))

		return;



	link = bpf_program__attach_tcx(skel->progs.change_tail, LO_IFINDEX,

				     &tcx_opts);

	if (!ASSERT_OK_PTR(link, "bpf_program__attach_tcx"))

		goto destroy;



	skel->links.change_tail = link;

	ret = create_pair(AF_INET, SOCK_DGRAM, &c1, &p1);

	if (!ASSERT_OK(ret, "create_pair"))

		goto destroy;



	ret = xsend(p1, "Tr", 2, 0);

	ASSERT_EQ(ret, 2, "xsend(p1)");

	ret = recv(c1, buf, 2, 0);

	ASSERT_EQ(ret, 2, "recv(c1)");

	ASSERT_EQ(skel->data->change_tail_ret, 0, "change_tail_ret");



	ret = xsend(p1, "G", 1, 0);

	ASSERT_EQ(ret, 1, "xsend(p1)");

	ret = recv(c1, buf, 2, 0);

	ASSERT_EQ(ret, 1, "recv(c1)");

	ASSERT_EQ(skel->data->change_tail_ret, 0, "change_tail_ret");



	ret = xsend(p1, "E", 1, 0);

	ASSERT_EQ(ret, 1, "xsend(p1)");

	ret = recv(c1, buf, 1, 0);

	ASSERT_EQ(ret, 1, "recv(c1)");

	ASSERT_EQ(skel->data->change_tail_ret, -EINVAL, "change_tail_ret");



	ret = xsend(p1, "Z", 1, 0);

	ASSERT_EQ(ret, 1, "xsend(p1)");

	ret = recv(c1, buf, 1, 0);

	ASSERT_EQ(ret, 1, "recv(c1)");

	ASSERT_EQ(skel->data->change_tail_ret, -EINVAL, "change_tail_ret");



	close(c1);

	close(p1);

destroy:

	test_tc_change_tail__destroy(skel);

}

tools/testing/selftests/bpf/progs/test_tc_change_tail.c

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// 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";