[PATCH bpf-next 4/4] selftests/bpf: Add tests for bpf path iterator

[Song Liu]

Add tests for bpf path iterator, including test cases similar to real
workload (call bpf_path_d_path and bpf_get_dentry_xattr), and test cases
where the verifier rejects invalid use of the iterator.

Signed-off-by: Song Liu <song at kernel.org>
---
 .../testing/selftests/bpf/bpf_experimental.h  |   6 +
 .../selftests/bpf/prog_tests/path_iter.c      |  12 ++
 tools/testing/selftests/bpf/progs/path_iter.c | 134 ++++++++++++++++++
 3 files changed, 152 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/path_iter.c
 create mode 100644 tools/testing/selftests/bpf/progs/path_iter.c

diff --git a/tools/testing/selftests/bpf/bpf_experimental.h b/tools/testing/selftests/bpf/bpf_experimental.h
index 6535c8ae3c46..e9eb2b105eb2 100644
--- a/tools/testing/selftests/bpf/bpf_experimental.h
+++ b/tools/testing/selftests/bpf/bpf_experimental.h
@@ -591,4 +591,10 @@ extern int bpf_iter_kmem_cache_new(struct bpf_iter_kmem_cache *it) __weak __ksym
 extern struct kmem_cache *bpf_iter_kmem_cache_next(struct bpf_iter_kmem_cache *it) __weak __ksym;
 extern void bpf_iter_kmem_cache_destroy(struct bpf_iter_kmem_cache *it) __weak __ksym;
 
+struct bpf_iter_path;
+extern int bpf_iter_path_new(struct bpf_iter_path *it, struct path *start,
+			     enum bpf_path_iter_mode mode) __weak __ksym;
+extern struct path *bpf_iter_path_next(struct bpf_iter_path *it) __weak __ksym;
+extern void bpf_iter_path_destroy(struct bpf_iter_path *it) __weak __ksym;
+
 #endif
diff --git a/tools/testing/selftests/bpf/prog_tests/path_iter.c b/tools/testing/selftests/bpf/prog_tests/path_iter.c
new file mode 100644
index 000000000000..3c99c24fbd96
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/path_iter.c
@@ -0,0 +1,12 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2025 Meta Platforms, Inc. and affiliates. */
+
+#include <test_progs.h>
+#include <bpf/libbpf.h>
+#include <bpf/btf.h>
+#include "path_iter.skel.h"
+
+void test_path_iter(void)
+{
+	RUN_TESTS(path_iter);
+}
diff --git a/tools/testing/selftests/bpf/progs/path_iter.c b/tools/testing/selftests/bpf/progs/path_iter.c
new file mode 100644
index 000000000000..d5733c797a3f
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/path_iter.c
@@ -0,0 +1,134 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2025 Meta Platforms, Inc. and affiliates. */
+
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+#include "bpf_misc.h"
+#include "bpf_experimental.h"
+
+char _license[] SEC("license") = "GPL";
+
+char path_name[256];
+char xattr_val[64];
+
+static __always_inline void access_path_dentry(struct path *p)
+{
+	struct bpf_dynptr ptr;
+	struct dentry *dentry;
+
+	if (!p)
+		return;
+
+	bpf_dynptr_from_mem(xattr_val, sizeof(xattr_val), 0, &ptr);
+	bpf_path_d_path(p, path_name, sizeof(path_name));
+
+	dentry = p->dentry;
+	if (dentry)
+		bpf_get_dentry_xattr(dentry, "user.xattr", &ptr);
+}
+
+SEC("lsm.s/file_open")
+__success
+int BPF_PROG(open_code, struct file *f)
+{
+	struct bpf_iter_path path_it;
+	struct path *p;
+	int ret;
+
+	ret = bpf_iter_path_new(&path_it, &f->f_path, BPF_PATH_ITER_MODE_PARENT);
+	if (ret) {
+		bpf_iter_path_destroy(&path_it);
+		return 0;
+	}
+
+	p = bpf_iter_path_next(&path_it);
+	access_path_dentry(p);
+	bpf_iter_path_destroy(&path_it);
+
+	return 0;
+}
+
+SEC("lsm.s/file_open")
+__success
+int BPF_PROG(for_each, struct file *f)
+{
+	struct path *p;
+
+	bpf_for_each(path, p, &f->f_path, BPF_PATH_ITER_MODE_PARENT)
+		access_path_dentry(p);
+
+	return 0;
+}
+
+SEC("lsm.s/file_open")
+__failure __msg("Unreleased reference")
+int BPF_PROG(missing_destroy, struct file *f)
+{
+	struct bpf_iter_path path_it;
+
+	bpf_iter_path_new(&path_it, &f->f_path, BPF_PATH_ITER_MODE_PARENT);
+
+	return 0;
+}
+
+SEC("lsm.s/file_open")
+__failure __msg("expected an initialized iter_path")
+int BPF_PROG(missing_new, struct file *f)
+{
+	struct bpf_iter_path path_it;
+
+	bpf_iter_path_destroy(&path_it);
+	return 0;
+}
+
+SEC("lsm.s/file_open")
+__failure __msg("expected uninitialized iter_path")
+int BPF_PROG(new_twice, struct file *f)
+{
+	struct bpf_iter_path path_it;
+
+	bpf_iter_path_new(&path_it, &f->f_path, BPF_PATH_ITER_MODE_PARENT);
+	bpf_iter_path_new(&path_it, &f->f_path, BPF_PATH_ITER_MODE_PARENT);
+	bpf_iter_path_destroy(&path_it);
+	return 0;
+}
+
+SEC("lsm.s/file_open")
+__failure __msg("expected an initialized iter_path")
+int BPF_PROG(destroy_twice, struct file *f)
+{
+	struct bpf_iter_path path_it;
+
+	bpf_iter_path_new(&path_it, &f->f_path, BPF_PATH_ITER_MODE_PARENT);
+	bpf_iter_path_destroy(&path_it);
+	bpf_iter_path_destroy(&path_it);
+	return 0;
+}
+
+SEC("lsm.s/file_open")
+__success
+int BPF_PROG(reuse_path_iter, struct file *f)
+{
+	struct bpf_iter_path path_it;
+
+	bpf_iter_path_new(&path_it, &f->f_path, BPF_PATH_ITER_MODE_PARENT);
+	bpf_iter_path_destroy(&path_it);
+	bpf_iter_path_new(&path_it, &f->f_path, BPF_PATH_ITER_MODE_PARENT);
+	bpf_iter_path_destroy(&path_it);
+	return 0;
+}
+
+SEC("lsm.s/file_open")
+__failure __msg("invalid read from stack off")
+int BPF_PROG(invalid_read_path_iter, struct file *f)
+{
+	struct bpf_iter_path path_it;
+	struct bpf_iter_path path_it_2;
+
+
+	bpf_iter_path_new(&path_it, &f->f_path, BPF_PATH_ITER_MODE_PARENT);
+	path_it_2 = path_it;
+	bpf_iter_path_destroy(&path_it_2);
+	return 0;
+}
-- 
2.47.1