selftests/bpf: Add a BPF selftest for bpf_skb_change_tail()

As requested by Daniel, we need to add a selftest to cover
bpf_skb_change_tail() cases in skb_verdict. Here we test trimming,
growing and error cases, and validate its expected return values and the
expected sizes of the payload.

Signed-off-by: Cong Wang <cong.wang@bytedance.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/bpf/20241213034057.246437-3-xiyou.wangcong@gmail.com

diff --git a/tools/testing/selftests/bpf/prog_tests/sockmap_basic.c b/tools/testing/selftests/bpf/prog_tests/sockmap_basic.c
index 248754296d972286e45d79331e95a8a6ae824590..884ad87783d59ef3d1ca84c3a542f3f8670cd463 100644 (file)
--- a/tools/testing/selftests/bpf/prog_tests/sockmap_basic.c
+++ b/tools/testing/selftests/bpf/prog_tests/sockmap_basic.c
@@ -12,6 +12,7 @@
 #include "test_sockmap_progs_query.skel.h"
 #include "test_sockmap_pass_prog.skel.h"
 #include "test_sockmap_drop_prog.skel.h"
+#include "test_sockmap_change_tail.skel.h"
 #include "bpf_iter_sockmap.skel.h"
 
 #include "sockmap_helpers.h"
@@ -643,6 +644,54 @@ out:
                test_sockmap_drop_prog__destroy(drop);
 }
 
+static void test_sockmap_skb_verdict_change_tail(void)
+{
+       struct test_sockmap_change_tail *skel;
+       int err, map, verdict;
+       int c1, p1, sent, recvd;
+       int zero = 0;
+       char buf[2];
+
+       skel = test_sockmap_change_tail__open_and_load();
+       if (!ASSERT_OK_PTR(skel, "open_and_load"))
+               return;
+       verdict = bpf_program__fd(skel->progs.prog_skb_verdict);
+       map = bpf_map__fd(skel->maps.sock_map_rx);
+
+       err = bpf_prog_attach(verdict, map, BPF_SK_SKB_STREAM_VERDICT, 0);
+       if (!ASSERT_OK(err, "bpf_prog_attach"))
+               goto out;
+       err = create_pair(AF_INET, SOCK_STREAM, &c1, &p1);
+       if (!ASSERT_OK(err, "create_pair()"))
+               goto out;
+       err = bpf_map_update_elem(map, &zero, &c1, BPF_NOEXIST);
+       if (!ASSERT_OK(err, "bpf_map_update_elem(c1)"))
+               goto out_close;
+       sent = xsend(p1, "Tr", 2, 0);
+       ASSERT_EQ(sent, 2, "xsend(p1)");
+       recvd = recv(c1, buf, 2, 0);
+       ASSERT_EQ(recvd, 1, "recv(c1)");
+       ASSERT_EQ(skel->data->change_tail_ret, 0, "change_tail_ret");
+
+       sent = xsend(p1, "G", 1, 0);
+       ASSERT_EQ(sent, 1, "xsend(p1)");
+       recvd = recv(c1, buf, 2, 0);
+       ASSERT_EQ(recvd, 2, "recv(c1)");
+       ASSERT_EQ(skel->data->change_tail_ret, 0, "change_tail_ret");
+
+       sent = xsend(p1, "E", 1, 0);
+       ASSERT_EQ(sent, 1, "xsend(p1)");
+       recvd = recv(c1, buf, 1, 0);
+       ASSERT_EQ(recvd, 1, "recv(c1)");
+       ASSERT_EQ(skel->data->change_tail_ret, -EINVAL, "change_tail_ret");
+
+out_close:
+       close(c1);
+       close(p1);
+out:
+       test_sockmap_change_tail__destroy(skel);
+}
+
 static void test_sockmap_skb_verdict_peek_helper(int map)
 {
        int err, c1, p1, zero = 0, sent, recvd, avail;
@@ -1058,6 +1107,8 @@ void test_sockmap_basic(void)
                test_sockmap_skb_verdict_fionread(true);
        if (test__start_subtest("sockmap skb_verdict fionread on drop"))
                test_sockmap_skb_verdict_fionread(false);
+       if (test__start_subtest("sockmap skb_verdict change tail"))
+               test_sockmap_skb_verdict_change_tail();
        if (test__start_subtest("sockmap skb_verdict msg_f_peek"))
                test_sockmap_skb_verdict_peek();
        if (test__start_subtest("sockmap skb_verdict msg_f_peek with link"))

diff --git a/tools/testing/selftests/bpf/progs/test_sockmap_change_tail.c b/tools/testing/selftests/bpf/progs/test_sockmap_change_tail.c
new file mode 100644 (file)
index 0000000..2796dd8
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/test_sockmap_change_tail.c
@@ -0,0 +1,40 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2024 ByteDance */
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+
+struct {
+       __uint(type, BPF_MAP_TYPE_SOCKMAP);
+       __uint(max_entries, 1);
+       __type(key, int);
+       __type(value, int);
+} sock_map_rx SEC(".maps");
+
+long change_tail_ret = 1;
+
+SEC("sk_skb")
+int prog_skb_verdict(struct __sk_buff *skb)
+{
+       char *data, *data_end;
+
+       bpf_skb_pull_data(skb, 1);
+       data = (char *)(unsigned long)skb->data;
+       data_end = (char *)(unsigned long)skb->data_end;
+
+       if (data + 1 > data_end)
+               return SK_PASS;
+
+       if (data[0] == 'T') { /* Trim the packet */
+               change_tail_ret = bpf_skb_change_tail(skb, skb->len - 1, 0);
+               return SK_PASS;
+       } else if (data[0] == 'G') { /* Grow the packet */
+               change_tail_ret = bpf_skb_change_tail(skb, skb->len + 1, 0);
+               return SK_PASS;
+       } else if (data[0] == 'E') { /* Error */
+               change_tail_ret = bpf_skb_change_tail(skb, 65535, 0);
+               return SK_PASS;
+       }
+       return SK_PASS;
+}
+
+char _license[] SEC("license") = "GPL";