selftests/bpf: add tests for LIBBPF_BPF_TOKEN_PATH envvar

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>
Link: https://lore.kernel.org/r/20231213190842.3844987-11-andrii@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

diff --git a/tools/testing/selftests/bpf/prog_tests/token.c b/tools/testing/selftests/bpf/prog_tests/token.c
index 1a3c3aacf5378e44ceb8af9ff1db74f7d9d6d8ca..548aeb91ab0dc5f383a12cc48590f633b6a616e6 100644 (file)
--- a/tools/testing/selftests/bpf/prog_tests/token.c
+++ b/tools/testing/selftests/bpf/prog_tests/token.c
@@ -769,6 +769,9 @@ 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);
@@ -791,6 +794,20 @@ 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
         */
@@ -826,6 +843,90 @@ 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;
+
+       /* now disable implicit token through negative bpf_token_fd, envvar
+        * will be ignored, should fail
+        */
+       opts.bpf_token_path = NULL;
+       opts.bpf_token_fd = -1;
+       skel = dummy_st_ops_success__open_opts(&opts);
+       if (!ASSERT_OK_PTR(skel, "obj_neg_token_fd_open"))
+               goto err_out;
+
+       err = dummy_st_ops_success__load(skel);
+       dummy_st_ops_success__destroy(skel);
+       if (!ASSERT_ERR(err, "obj_neg_token_fd_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)
@@ -904,4 +1005,15 @@ 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);
+       }
 }