[PATCH bpf-next 8/8] selftests/bpf: add tests for BPF object load with implicit token

From: Andrii Nakryiko <andrii@kernel.org>
To: <bpf@vger.kernel.org>, <netdev@vger.kernel.org>,
	<paul@paul-moore.com>, <brauner@kernel.org>
Cc: <linux-fsdevel@vger.kernel.org>,
	<linux-security-module@vger.kernel.org>, <keescook@chromium.org>,
	<kernel-team@meta.com>, <sargun@sargun.me>
Subject: [PATCH bpf-next 8/8] selftests/bpf: add tests for BPF object load with implicit token
Date: Thu, 7 Dec 2023 10:54:43 -0800	[thread overview]
Message-ID: <20231207185443.2297160-9-andrii@kernel.org> (raw)
In-Reply-To: <20231207185443.2297160-1-andrii@kernel.org>

Add a test to validate libbpf's implicit BPF token creation from default
BPF FS location (/sys/fs/bpf). Also validate that disabling this
implicit BPF token creation works.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
---
 .../testing/selftests/bpf/prog_tests/token.c  | 76 +++++++++++++++++++
 1 file changed, 76 insertions(+)

diff --git a/tools/testing/selftests/bpf/prog_tests/token.c b/tools/testing/selftests/bpf/prog_tests/token.c
index 9812292336c9..1a3c3aacf537 100644
--- a/tools/testing/selftests/bpf/prog_tests/token.c
+++ b/tools/testing/selftests/bpf/prog_tests/token.c
@@ -12,6 +12,7 @@
 #include <linux/unistd.h>
 #include <linux/mount.h>
 #include <sys/socket.h>
+#include <sys/stat.h>
 #include <sys/syscall.h>
 #include <sys/un.h>
 #include "priv_map.skel.h"
@@ -45,6 +46,13 @@ static inline int sys_fsmount(int fs_fd, unsigned flags, unsigned ms_flags)
 	return syscall(__NR_fsmount, fs_fd, flags, ms_flags);
 }
 
+static inline int sys_move_mount(int from_dfd, const char *from_path,
+				 int to_dfd, const char *to_path,
+				 unsigned flags)
+{
+	return syscall(__NR_move_mount, from_dfd, from_path, to_dfd, to_path, flags);
+}
+
 static int drop_priv_caps(__u64 *old_caps)
 {
 	return cap_disable_effective((1ULL << CAP_BPF) |
@@ -761,6 +769,63 @@ static int userns_obj_priv_btf_success(int mnt_fd)
 	return validate_struct_ops_load(mnt_fd, true /* should succeed */);
 }
 
+static int userns_obj_priv_implicit_token(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 /sys/fs/bpf so that libbpf can create BPF
+	 * token automatically and implicitly
+	 */
+	err = sys_move_mount(mnt_fd, "", AT_FDCWD, "/sys/fs/bpf", MOVE_MOUNT_F_EMPTY_PATH);
+	if (!ASSERT_OK(err, "move_mount_bpffs"))
+		return -EINVAL;
+
+	/* now the same struct_ops skeleton should succeed thanks to libppf
+	 * creating BPF token from /sys/fs/bpf mount point
+	 */
+	skel = dummy_st_ops_success__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "obj_implicit_token_load"))
+		return -EINVAL;
+
+	dummy_st_ops_success__destroy(skel);
+
+	/* now disable implicit token through empty bpf_token_path, should fail */
+	opts.bpf_token_path = "";
+	skel = dummy_st_ops_success__open_opts(&opts);
+	if (!ASSERT_OK_PTR(skel, "obj_empty_token_path_open"))
+		return -EINVAL;
+
+	err = dummy_st_ops_success__load(skel);
+	dummy_st_ops_success__destroy(skel);
+	if (!ASSERT_ERR(err, "obj_empty_token_path_load"))
+		return -EINVAL;
+
+	/* now disable implicit token through negative bpf_token_fd, 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"))
+		return -EINVAL;
+
+	err = dummy_st_ops_success__load(skel);
+	dummy_st_ops_success__destroy(skel);
+	if (!ASSERT_ERR(err, "obj_neg_token_fd_load"))
+		return -EINVAL;
+
+	return 0;
+}
+
 #define bit(n) (1ULL << (n))
 
 void test_token(void)
@@ -828,4 +893,15 @@ void test_token(void)
 
 		subtest_userns(&opts, userns_obj_priv_btf_success);
 	}
+	if (test__start_subtest("obj_priv_implicit_token")) {
+		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);
+	}
 }
-- 
2.34.1

