selftests/bpf: Reject graph kptr use after RCU unlockgrafted

Add a sleepable verifier test that loads a graph-node local kptr in an
explicit RCU read-side critical section, then passes its node to
bpf_rbtree_remove() after the section ends.

Before the verifier fix, the stale NON_OWN_REF flag makes the node look like
a live borrowed reference and the program is accepted. After the fix, the
pointer is demoted without NON_OWN_REF and the graph kfunc argument is
rejected.

Also exercise a graph kptr loaded while a spin lock provides implicit RCU
protection. The pointer must be invalidated when the lock is released, which
guards the required ordering between non-owning-reference invalidation and
RCU demotion.

Update the existing fault-protected load test state description. The
post-unlock pointer no longer carries NON_OWN_REF, but remains readable
because the load is rewritten to use BPF_PROBE_MEM.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20260904084325.52250-7-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 81 insertions, 0 deletions

diff --git a/security/landlock/setup.c b/security/landlock/setup.c
new file mode 100644
index 000000000..47dac1736
--- /dev/null
+++ b/security/landlock/setup.c
@@ -0,0 +1,81 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Landlock LSM - Security framework setup
+ *
+ * Copyright © 2016-2020 Mickaël Salaün <mic@digikod.net>
+ * Copyright © 2018-2020 ANSSI
+ */
+
+#include <linux/bits.h>
+#include <linux/init.h>
+#include <linux/lsm_hooks.h>
+#include <uapi/linux/lsm.h>
+
+#include "common.h"
+#include "cred.h"
+#include "errata.h"
+#include "fs.h"
+#include "id.h"
+#include "net.h"
+#include "setup.h"
+#include "task.h"
+
+bool landlock_initialized __ro_after_init = false;
+
+const struct lsm_id landlock_lsmid = {
+	.name = LANDLOCK_NAME,
+	.id = LSM_ID_LANDLOCK,
+};
+
+struct lsm_blob_sizes landlock_blob_sizes __ro_after_init = {
+	.lbs_cred = sizeof(struct landlock_cred_security),
+	.lbs_file = sizeof(struct landlock_file_security),
+	.lbs_inode = sizeof(struct landlock_inode_security),
+	.lbs_superblock = sizeof(struct landlock_superblock_security),
+};
+
+int landlock_errata __ro_after_init;
+
+static void __init compute_errata(void)
+{
+	size_t i;
+
+#ifndef __has_include
+	/*
+	 * This is a safeguard to make sure the compiler implements
+	 * __has_include (see errata.h).
+	 */
+	WARN_ON_ONCE(1);
+	return;
+#endif
+
+	for (i = 0; landlock_errata_init[i].number; i++) {
+		const int prev_errata = landlock_errata;
+
+		if (WARN_ON_ONCE(landlock_errata_init[i].abi >
+				 landlock_abi_version))
+			continue;
+
+		landlock_errata |= BIT(landlock_errata_init[i].number - 1);
+		WARN_ON_ONCE(prev_errata == landlock_errata);
+	}
+}
+
+static int __init landlock_init(void)
+{
+	compute_errata();
+	landlock_add_cred_hooks();
+	landlock_add_task_hooks();
+	landlock_add_fs_hooks();
+	landlock_add_net_hooks();
+	landlock_init_id();
+	landlock_initialized = true;
+	pr_info("Up and running.\n");
+	return 0;
+}
+
+DEFINE_LSM(LANDLOCK_NAME) = {
+	.id = &landlock_lsmid,
+	.init = landlock_init,
+	.blobs = &landlock_blob_sizes,
+};