selftests/bpf: Excercise bpf_obj_get_info_by_fd for bpf2bpf

Apparently, no existing selftest covers it. Add a new one where
we load cgroup/bind4 program and attach fentry to it. Calling
bpf_obj_get_info_by_fd on the fentry program should return non-zero
btf_id/btf_obj_id instead of crashing the kernel.

Signed-off-by: Stanislav Fomichev <sdf@google.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Link: https://lore.kernel.org/bpf/20220804201140.1340684-2-sdf@google.com

diff --git a/tools/testing/selftests/bpf/prog_tests/fexit_bpf2bpf.c b/tools/testing/selftests/bpf/prog_tests/fexit_bpf2bpf.c
index 02bb8cb..da860b0 100644 (file)
--- a/tools/testing/selftests/bpf/prog_tests/fexit_bpf2bpf.c
+++ b/tools/testing/selftests/bpf/prog_tests/fexit_bpf2bpf.c
@@ -3,6 +3,7 @@
 #include <test_progs.h>
 #include <network_helpers.h>
 #include <bpf/btf.h>
+#include "bind4_prog.skel.h"
 
 typedef int (*test_cb)(struct bpf_object *obj);
 
@@ -407,6 +408,98 @@ static void test_func_replace_global_func(void)
                                  prog_name, false, NULL);
 }
 
+static int find_prog_btf_id(const char *name, __u32 attach_prog_fd)
+{
+       struct bpf_prog_info info = {};
+       __u32 info_len = sizeof(info);
+       struct btf *btf;
+       int ret;
+
+       ret = bpf_obj_get_info_by_fd(attach_prog_fd, &info, &info_len);
+       if (ret)
+               return ret;
+
+       if (!info.btf_id)
+               return -EINVAL;
+
+       btf = btf__load_from_kernel_by_id(info.btf_id);
+       ret = libbpf_get_error(btf);
+       if (ret)
+               return ret;
+
+       ret = btf__find_by_name_kind(btf, name, BTF_KIND_FUNC);
+       btf__free(btf);
+       return ret;
+}
+
+static int load_fentry(int attach_prog_fd, int attach_btf_id)
+{
+       LIBBPF_OPTS(bpf_prog_load_opts, opts,
+                   .expected_attach_type = BPF_TRACE_FENTRY,
+                   .attach_prog_fd = attach_prog_fd,
+                   .attach_btf_id = attach_btf_id,
+       );
+       struct bpf_insn insns[] = {
+               BPF_MOV64_IMM(BPF_REG_0, 0),
+               BPF_EXIT_INSN(),
+       };
+
+       return bpf_prog_load(BPF_PROG_TYPE_TRACING,
+                            "bind4_fentry",
+                            "GPL",
+                            insns,
+                            ARRAY_SIZE(insns),
+                            &opts);
+}
+
+static void test_fentry_to_cgroup_bpf(void)
+{
+       struct bind4_prog *skel = NULL;
+       struct bpf_prog_info info = {};
+       __u32 info_len = sizeof(info);
+       int cgroup_fd = -1;
+       int fentry_fd = -1;
+       int btf_id;
+
+       cgroup_fd = test__join_cgroup("/fentry_to_cgroup_bpf");
+       if (!ASSERT_GE(cgroup_fd, 0, "cgroup_fd"))
+               return;
+
+       skel = bind4_prog__open_and_load();
+       if (!ASSERT_OK_PTR(skel, "skel"))
+               goto cleanup;
+
+       skel->links.bind_v4_prog = bpf_program__attach_cgroup(skel->progs.bind_v4_prog, cgroup_fd);
+       if (!ASSERT_OK_PTR(skel->links.bind_v4_prog, "bpf_program__attach_cgroup"))
+               goto cleanup;
+
+       btf_id = find_prog_btf_id("bind_v4_prog", bpf_program__fd(skel->progs.bind_v4_prog));
+       if (!ASSERT_GE(btf_id, 0, "find_prog_btf_id"))
+               goto cleanup;
+
+       fentry_fd = load_fentry(bpf_program__fd(skel->progs.bind_v4_prog), btf_id);
+       if (!ASSERT_GE(fentry_fd, 0, "load_fentry"))
+               goto cleanup;
+
+       /* Make sure bpf_obj_get_info_by_fd works correctly when attaching
+        * to another BPF program.
+        */
+
+       ASSERT_OK(bpf_obj_get_info_by_fd(fentry_fd, &info, &info_len),
+                 "bpf_obj_get_info_by_fd");
+
+       ASSERT_EQ(info.btf_id, 0, "info.btf_id");
+       ASSERT_EQ(info.attach_btf_id, btf_id, "info.attach_btf_id");
+       ASSERT_GT(info.attach_btf_obj_id, 0, "info.attach_btf_obj_id");
+
+cleanup:
+       if (cgroup_fd >= 0)
+               close(cgroup_fd);
+       if (fentry_fd >= 0)
+               close(fentry_fd);
+       bind4_prog__destroy(skel);
+}
+
 /* NOTE: affect other tests, must run in serial mode */
 void serial_test_fexit_bpf2bpf(void)
 {
@@ -430,4 +523,6 @@ void serial_test_fexit_bpf2bpf(void)
                test_fmod_ret_freplace();
        if (test__start_subtest("func_replace_global_func"))
                test_func_replace_global_func();
+       if (test__start_subtest("fentry_to_cgroup_bpf"))
+               test_fentry_to_cgroup_bpf();
 }