[PATCH bpf-next 29/29] selftests/bpf: add tests for LIBBPF_BPF_TOKEN_PATH envvar

Andrii Nakryiko
2024-01-03T22:24:46Z

Add new subtest validating LIBBPF_BPF_TOKEN_PATH envvar semantics.
Extend existing test to validate that LIBBPF_BPF_TOKEN_PATH allows to
disable implicit BPF token creation by setting envvar to empty string.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
---
.../testing/selftests/bpf/prog_tests/token.c | 98 +++++++++++++++++++
1 file changed, 98 insertions(+)

diff --git a/tools/testing/selftests/bpf/prog_tests/token.c b/tools/testing/selftests/bpf/prog_tests/token.c
index 003f7c208f4c..1f6aa685e6f7 100644
--- a/tools/testing/selftests/bpf/prog_tests/token.c
+++ b/tools/testing/selftests/bpf/prog_tests/token.c
@@ -773,6 +773,9 @@ static int userns_obj_priv_btf_success(int mnt_fd)
return validate_struct_ops_load(mnt_fd, true /* should succeed */);
}

+#define TOKEN_ENVVAR "LIBBPF_BPF_TOKEN_PATH"
+#define TOKEN_BPFFS_CUSTOM "/bpf-token-fs"
+
static int userns_obj_priv_implicit_token(int mnt_fd)
{
LIBBPF_OPTS(bpf_object_open_opts, opts);
@@ -795,6 +798,20 @@ static int userns_obj_priv_implicit_token(int mnt_fd)
if (!ASSERT_OK(err, "move_mount_bpffs"))
return -EINVAL;

+ /* disable implicit BPF token creation by setting
+ * LIBBPF_BPF_TOKEN_PATH envvar to empty value, load should fail
+ */
+ err = setenv(TOKEN_ENVVAR, "", 1 /*overwrite*/);
+ if (!ASSERT_OK(err, "setenv_token_path"))
+ return -EINVAL;
+ skel = dummy_st_ops_success__open_and_load();
+ if (!ASSERT_ERR_PTR(skel, "obj_token_envvar_disabled_load")) {
+ unsetenv(TOKEN_ENVVAR);
+ dummy_st_ops_success__destroy(skel);
+ return -EINVAL;
+ }
+ unsetenv(TOKEN_ENVVAR);
+
/* now the same struct_ops skeleton should succeed thanks to libppf
* creating BPF token from /sys/fs/bpf mount point
*/
@@ -818,6 +835,76 @@ static int userns_obj_priv_implicit_token(int mnt_fd)
return 0;
}

+static int userns_obj_priv_implicit_token_envvar(int mnt_fd)
+{
+ LIBBPF_OPTS(bpf_object_open_opts, opts);
+ struct dummy_st_ops_success *skel;
+ int err;
+
+ /* before we mount BPF FS with token delegation, struct_ops skeleton
+ * should fail to load
+ */
+ skel = dummy_st_ops_success__open_and_load();
+ if (!ASSERT_ERR_PTR(skel, "obj_tokenless_load")) {
+ dummy_st_ops_success__destroy(skel);
+ return -EINVAL;
+ }
+
+ /* mount custom BPF FS over custom location, so libbpf can't create
+ * BPF token implicitly, unless pointed to it through
+ * LIBBPF_BPF_TOKEN_PATH envvar
+ */
+ rmdir(TOKEN_BPFFS_CUSTOM);
+ if (!ASSERT_OK(mkdir(TOKEN_BPFFS_CUSTOM, 0777), "mkdir_bpffs_custom"))
+ goto err_out;
+ err = sys_move_mount(mnt_fd, "", AT_FDCWD, TOKEN_BPFFS_CUSTOM, MOVE_MOUNT_F_EMPTY_PATH);
+ if (!ASSERT_OK(err, "move_mount_bpffs"))
+ goto err_out;
+
+ /* even though we have BPF FS with delegation, it's not at default
+ * /sys/fs/bpf location, so we still fail to load until envvar is set up
+ */
+ skel = dummy_st_ops_success__open_and_load();
+ if (!ASSERT_ERR_PTR(skel, "obj_tokenless_load2")) {
+ dummy_st_ops_success__destroy(skel);
+ goto err_out;
+ }
+
+ err = setenv(TOKEN_ENVVAR, TOKEN_BPFFS_CUSTOM, 1 /*overwrite*/);
+ if (!ASSERT_OK(err, "setenv_token_path"))
+ goto err_out;
+
+ /* now the same struct_ops skeleton should succeed thanks to libppf
+ * creating BPF token from custom mount point
+ */
+ skel = dummy_st_ops_success__open_and_load();
+ if (!ASSERT_OK_PTR(skel, "obj_implicit_token_load"))
+ goto err_out;
+
+ dummy_st_ops_success__destroy(skel);
+
+ /* now disable implicit token through empty bpf_token_path, envvar
+ * will be ignored, should fail
+ */
+ opts.bpf_token_path = "";
+ skel = dummy_st_ops_success__open_opts(&opts);
+ if (!ASSERT_OK_PTR(skel, "obj_empty_token_path_open"))
+ goto err_out;
+
+ err = dummy_st_ops_success__load(skel);
+ dummy_st_ops_success__destroy(skel);
+ if (!ASSERT_ERR(err, "obj_empty_token_path_load"))
+ goto err_out;
+
+ rmdir(TOKEN_BPFFS_CUSTOM);
+ unsetenv(TOKEN_ENVVAR);
+ return 0;
+err_out:
+ rmdir(TOKEN_BPFFS_CUSTOM);
+ unsetenv(TOKEN_ENVVAR);
+ return -EINVAL;
+}
+
#define bit(n) (1ULL << (n))

void test_token(void)
@@ -896,4 +983,15 @@ void test_token(void)

subtest_userns(&opts, userns_obj_priv_implicit_token);
}
+ if (test__start_subtest("obj_priv_implicit_token_envvar")) {
+ struct bpffs_opts opts = {
+ /* allow BTF loading */
+ .cmds = bit(BPF_BTF_LOAD) | bit(BPF_MAP_CREATE) | bit(BPF_PROG_LOAD),
+ .maps = bit(BPF_MAP_TYPE_STRUCT_OPS),
+ .progs = bit(BPF_PROG_TYPE_STRUCT_OPS),
+ .attachs = ~0ULL,
+ };
+
+ subtest_userns(&opts, userns_obj_priv_implicit_token_envvar);
+ }
}
--
2.34.1