[PATCH v2 bpf-next 7/9] bpf/selftests: add selftests for root/pwd path based BPF kfuncs

[Matt Bobrowski <mattbobrowski@google.com>]

Add a new path_kfunc test suite that is responsible for verifiying the
operability of the newly added root/pwd path based BPF kfuncs. This
test suite covers the following BPF kfuncs:

struct path *bpf_get_task_fs_root(struct task_struct *task);
struct path *bpf_get_task_fs_pwd(struct task_struct *task);
void bpf_put_path(struct path *path);

Signed-off-by: Matt Bobrowski <mattbobrowski@google.com>
---
 .../selftests/bpf/prog_tests/path_kfunc.c     |  48 ++++++++
 .../selftests/bpf/progs/path_kfunc_common.h   |  20 +++
 .../selftests/bpf/progs/path_kfunc_failure.c  | 114 ++++++++++++++++++
 .../selftests/bpf/progs/path_kfunc_success.c  |  30 +++++
 4 files changed, 212 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/path_kfunc.c
 create mode 100644 tools/testing/selftests/bpf/progs/path_kfunc_common.h
 create mode 100644 tools/testing/selftests/bpf/progs/path_kfunc_failure.c
 create mode 100644 tools/testing/selftests/bpf/progs/path_kfunc_success.c

diff --git a/tools/testing/selftests/bpf/prog_tests/path_kfunc.c b/tools/testing/selftests/bpf/prog_tests/path_kfunc.c
new file mode 100644
index 000000000000..9a8701a7999c
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/path_kfunc.c
@@ -0,0 +1,48 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2024 Google LLC. */
+
+#define _GNU_SOURCE
+#include <test_progs.h>
+
+#include "path_kfunc_failure.skel.h"
+#include "path_kfunc_success.skel.h"
+
+static void run_test(const char *prog_name)
+{
+	struct bpf_link *link;
+	struct bpf_program *prog;
+	struct path_kfunc_success *skel;
+
+	skel = path_kfunc_success__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "path_kfunc_success__open_and_load"))
+		return;
+
+	link = NULL;
+	prog = bpf_object__find_program_by_name(skel->obj, prog_name);
+	if (!ASSERT_OK_PTR(prog, "bpf_object__find_program_by_name"))
+		goto cleanup;
+
+	link = bpf_program__attach(prog);
+	ASSERT_OK_PTR(link, "bpf_program__attach");
+cleanup:
+	bpf_link__destroy(link);
+	path_kfunc_success__destroy(skel);
+}
+
+static const char * const success_tests[] = {
+	"get_task_fs_root_and_put_from_current",
+	"get_task_fs_pwd_and_put_from_current",
+};
+
+void test_path_kfunc(void)
+{
+	int i = 0;
+
+	for (; i < ARRAY_SIZE(success_tests); i++) {
+		if (!test__start_subtest(success_tests[i]))
+			continue;
+		run_test(success_tests[i]);
+	}
+
+	RUN_TESTS(path_kfunc_failure);
+}
diff --git a/tools/testing/selftests/bpf/progs/path_kfunc_common.h b/tools/testing/selftests/bpf/progs/path_kfunc_common.h
new file mode 100644
index 000000000000..837dc03c136d
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/path_kfunc_common.h
@@ -0,0 +1,20 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2024 Google LLC. */
+
+#ifndef _PATH_KFUNC_COMMON_H
+#define _PATH_KFUNC_COMMON_H
+
+#include <vmlinux.h>
+#include <errno.h>
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+
+#include "bpf_misc.h"
+
+char _license[] SEC("license") = "GPL";
+
+struct path *bpf_get_task_fs_root(struct task_struct *task) __ksym;
+struct path *bpf_get_task_fs_pwd(struct task_struct *task) __ksym;
+void bpf_put_path(struct path *path) __ksym;
+
+#endif /* _PATH_KFUNC_COMMON_H */
diff --git a/tools/testing/selftests/bpf/progs/path_kfunc_failure.c b/tools/testing/selftests/bpf/progs/path_kfunc_failure.c
new file mode 100644
index 000000000000..a28797e245e3
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/path_kfunc_failure.c
@@ -0,0 +1,114 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2024 Google LLC. */
+
+#include "path_kfunc_common.h"
+
+SEC("lsm.s/file_open")
+__failure __msg("Possibly NULL pointer passed to trusted arg0")
+int BPF_PROG(get_task_fs_root_kfunc_null)
+{
+	struct path *acquired;
+
+	/* Can't pass a NULL pointer to bpf_get_task_fs_root(). */
+	acquired = bpf_get_task_fs_root(NULL);
+	if (!acquired)
+		return 0;
+	bpf_put_path(acquired);
+
+	return 0;
+}
+
+SEC("lsm.s/file_open")
+__failure __msg("Possibly NULL pointer passed to trusted arg0")
+int BPF_PROG(get_task_fs_pwd_kfunc_null)
+{
+	struct path *acquired;
+
+	/* Can't pass a NULL pointer to bpf_get_task_fs_pwd(). */
+	acquired = bpf_get_task_fs_pwd(NULL);
+	if (!acquired)
+		return 0;
+	bpf_put_path(acquired);
+
+	return 0;
+}
+
+SEC("lsm.s/task_alloc")
+__failure __msg("R1 must be referenced or trusted")
+int BPF_PROG(get_task_fs_root_kfunc_untrusted, struct task_struct *task)
+{
+	struct path *acquired;
+	struct task_struct *parent;
+
+	/* Walking the struct task_struct will yield an untrusted pointer. */
+	parent = task->parent;
+	if (!parent)
+		return 0;
+
+	acquired = bpf_get_task_fs_root(parent);
+	if (!acquired)
+		return 0;
+	bpf_put_path(acquired);
+
+	return 0;
+}
+
+SEC("lsm.s/task_alloc")
+__failure __msg("R1 must be referenced or trusted")
+int BPF_PROG(get_task_fs_pwd_kfunc_untrusted, struct task_struct *task)
+{
+	struct path *acquired;
+	struct task_struct *parent;
+
+	/* Walking the struct task_struct will yield an untrusted pointer. */
+	parent = task->parent;
+	if (!parent)
+		return 0;
+
+	acquired = bpf_get_task_fs_pwd(parent);
+	if (!acquired)
+		return 0;
+	bpf_put_path(acquired);
+
+	return 0;
+}
+
+SEC("lsm.s/file_open")
+__failure __msg("Unreleased reference")
+int BPF_PROG(get_task_fs_root_kfunc_unreleased)
+{
+	struct path *acquired;
+
+	acquired = bpf_get_task_fs_root(bpf_get_current_task_btf());
+	if (!acquired)
+		return 0;
+	__sink(acquired);
+
+	/* Acquired but never released. */
+	return 0;
+}
+
+SEC("lsm.s/file_open")
+__failure __msg("Unreleased reference")
+int BPF_PROG(get_task_fs_pwd_kfunc_unreleased)
+{
+	struct path *acquired;
+
+	acquired = bpf_get_task_fs_pwd(bpf_get_current_task_btf());
+	if (!acquired)
+		return 0;
+	__sink(acquired);
+
+	/* Acquired but never released. */
+	return 0;
+}
+
+SEC("lsm.s/inode_getattr")
+__failure __msg("release kernel function bpf_put_path expects refcounted PTR_TO_BTF_ID")
+int BPF_PROG(put_path_kfunc_unacquired, struct path *path)
+{
+	/* Can't release an unacquired pointer. */
+	bpf_put_path(path);
+
+	return 0;
+}
diff --git a/tools/testing/selftests/bpf/progs/path_kfunc_success.c b/tools/testing/selftests/bpf/progs/path_kfunc_success.c
new file mode 100644
index 000000000000..8fc8e3c51405
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/path_kfunc_success.c
@@ -0,0 +1,30 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2024 Google LLC. */
+
+#include "path_kfunc_common.h"
+
+SEC("lsm.s/file_open")
+int BPF_PROG(get_task_fs_root_and_put_from_current)
+{
+	struct path *acquired;
+
+	acquired = bpf_get_task_fs_root(bpf_get_current_task_btf());
+	if (!acquired)
+		return 0;
+	bpf_put_path(acquired);
+
+	return 0;
+}
+
+SEC("lsm.s/file_open")
+int BPF_PROG(get_task_fs_pwd_and_put_from_current)
+{
+	struct path *acquired;
+
+	acquired = bpf_get_task_fs_pwd(bpf_get_current_task_btf());
+	if (!acquired)
+		return 0;
+	bpf_put_path(acquired);
+
+	return 0;
+}
-- 
2.44.0.278.ge034bb2e1d-goog

/M