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: Cong Wang <cong.wang@bytedance.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Tested-by: Zijian Zhang <zijianzhang@bytedance.com>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/bpf/20241213034057.246437-5-xiyou.wangcong@gmail.com

diff --git a/tools/testing/selftests/bpf/prog_tests/tc_change_tail.c b/tools/testing/selftests/bpf/prog_tests/tc_change_tail.c
new file mode 100644 (file)
index 0000000..7475223
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/tc_change_tail.c
@@ -0,0 +1,62 @@
+// 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);
+}

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 (file)
index 0000000..28edafe
--- /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";