Test bpf atomic inode xattr labeling in inode_init_security.

Signed-off-by: David Windsor <dwindsor@gmail.com>
---
 tools/testing/selftests/bpf/bpf_kfuncs.h      |  3 ++
 .../selftests/bpf/prog_tests/fs_kfuncs.c      | 49 +++++++++++++++++++
 .../bpf/progs/test_init_inode_xattr.c         | 32 ++++++++++++
 3 files changed, 84 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/progs/test_init_inode_xattr.c

diff --git a/tools/testing/selftests/bpf/bpf_kfuncs.h b/tools/testing/selftests/bpf/bpf_kfuncs.h
index ae71e9b69051..15507a406266 100644
--- a/tools/testing/selftests/bpf/bpf_kfuncs.h
+++ b/tools/testing/selftests/bpf/bpf_kfuncs.h
@@ -92,4 +92,7 @@ extern int bpf_set_dentry_xattr(struct dentry *dentry, const char *name__str,
 				const struct bpf_dynptr *value_p, int flags) __ksym __weak;
 extern int bpf_remove_dentry_xattr(struct dentry *dentry, const char *name__str) __ksym __weak;
 
+extern int bpf_init_inode_xattr(const char *name__str,
+				const struct bpf_dynptr *value_p) __ksym __weak;
+
 #endif
diff --git a/tools/testing/selftests/bpf/prog_tests/fs_kfuncs.c b/tools/testing/selftests/bpf/prog_tests/fs_kfuncs.c
index 43a26ec69a8e..26daef116ee2 100644
--- a/tools/testing/selftests/bpf/prog_tests/fs_kfuncs.c
+++ b/tools/testing/selftests/bpf/prog_tests/fs_kfuncs.c
@@ -9,6 +9,7 @@
 #include <test_progs.h>
 #include "test_get_xattr.skel.h"
 #include "test_set_remove_xattr.skel.h"
+#include "test_init_inode_xattr.skel.h"
 #include "test_fsverity.skel.h"
 
 static const char testfile[] = "/tmp/test_progs_fs_kfuncs";
@@ -268,6 +269,51 @@ static void test_fsverity(void)
 	remove(testfile);
 }
 
+static void test_init_inode_xattr(void)
+{
+	struct test_init_inode_xattr *skel = NULL;
+	int fd = -1, err;
+	char value_out[32];
+	const char *testfile_new = "/tmp/test_progs_fs_kfuncs_new";
+
+	skel = test_init_inode_xattr__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "test_init_inode_xattr__open_and_load"))
+		return;
+
+	skel->bss->monitored_pid = getpid();
+	err = test_init_inode_xattr__attach(skel);
+	if (!ASSERT_OK(err, "test_init_inode_xattr__attach"))
+		goto out;
+
+	/* Create a new file — this triggers inode_init_security */
+	fd = open(testfile_new, O_CREAT | O_RDWR, 0644);
+	if (!ASSERT_GE(fd, 0, "create_file"))
+		goto out;
+
+	ASSERT_EQ(skel->data->init_result, 0, "init_result");
+
+	/* The initxattrs callback prepends "security." to the name */
+	err = getxattr(testfile_new, "security.bpf.test_label", value_out,
+		       sizeof(value_out));
+	if (err < 0 && errno == ENODATA) {
+		printf("%s:SKIP:filesystem did not apply LSM xattrs\n",
+		       __func__);
+		test__skip();
+		goto out;
+	}
+	if (!ASSERT_GE(err, 0, "getxattr"))
+		goto out;
+
+	ASSERT_EQ(err, (int)sizeof(skel->data->xattr_value), "xattr_size");
+	ASSERT_EQ(strncmp(value_out, "test_value",
+			  sizeof("test_value")), 0, "xattr_value");
+
+out:
+	close(fd);
+	test_init_inode_xattr__destroy(skel);
+	remove(testfile_new);
+}
+
 void test_fs_kfuncs(void)
 {
 	/* Matches xattr_names in progs/test_get_xattr.c */
@@ -286,6 +332,9 @@ void test_fs_kfuncs(void)
 	if (test__start_subtest("set_remove_xattr"))
 		test_set_remove_xattr();
 
+	if (test__start_subtest("init_inode_xattr"))
+		test_init_inode_xattr();
+
 	if (test__start_subtest("fsverity"))
 		test_fsverity();
 }
diff --git a/tools/testing/selftests/bpf/progs/test_init_inode_xattr.c b/tools/testing/selftests/bpf/progs/test_init_inode_xattr.c
new file mode 100644
index 000000000000..450798893566
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/test_init_inode_xattr.c
@@ -0,0 +1,32 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2025 Isovalent, a Cisco company. */
+
+#include "vmlinux.h"
+#include <errno.h>
+#include <bpf/bpf_tracing.h>
+#include "bpf_kfuncs.h"
+
+char _license[] SEC("license") = "GPL";
+
+__u32 monitored_pid;
+int init_result = -1;
+
+const char xattr_name[] = "bpf.test_label";
+char xattr_value[] = "test_value";
+
+SEC("lsm/inode_init_security")
+int BPF_PROG(test_init_inode_xattr, struct inode *inode, struct inode *dir,
+	     const struct qstr *qstr, struct xattr *xattrs, int *xattr_count)
+{
+	struct bpf_dynptr value_ptr;
+	__u32 pid;
+
+	pid = bpf_get_current_pid_tgid() >> 32;
+	if (pid != monitored_pid)
+		return 0;
+
+	bpf_dynptr_from_mem(xattr_value, sizeof(xattr_value), 0, &value_ptr);
+	init_result = bpf_init_inode_xattr(xattr_name, &value_ptr);
+
+	return 0;
+}
-- 
2.53.0