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, 121 insertions, 0 deletions

diff --git a/fs/smb/smbdirect/main.c b/fs/smb/smbdirect/main.c
new file mode 100644
index 000000000..606732fef
--- /dev/null
+++ b/fs/smb/smbdirect/main.c
@@ -0,0 +1,121 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *   Copyright (c) 2025, Stefan Metzmacher
+ */
+
+#include "internal.h"
+#include <linux/module.h>
+
+struct smbdirect_module_state smbdirect_globals = {
+	.mutex = __MUTEX_INITIALIZER(smbdirect_globals.mutex),
+};
+
+static __init int smbdirect_module_init(void)
+{
+	int ret = -ENOMEM;
+
+	pr_notice("subsystem loading...\n");
+	mutex_lock(&smbdirect_globals.mutex);
+
+	smbdirect_globals.workqueues.accept = alloc_workqueue("smbdirect-accept",
+							      WQ_SYSFS |
+							      WQ_PERCPU |
+							      WQ_POWER_EFFICIENT,
+							      0);
+	if (smbdirect_globals.workqueues.accept == NULL)
+		goto alloc_accept_wq_failed;
+
+	smbdirect_globals.workqueues.connect = alloc_workqueue("smbdirect-connect",
+							       WQ_SYSFS |
+							       WQ_PERCPU |
+							       WQ_POWER_EFFICIENT,
+							       0);
+	if (smbdirect_globals.workqueues.connect == NULL)
+		goto alloc_connect_wq_failed;
+
+	smbdirect_globals.workqueues.idle = alloc_workqueue("smbdirect-idle",
+							    WQ_SYSFS |
+							    WQ_PERCPU |
+							    WQ_POWER_EFFICIENT,
+							    0);
+	if (smbdirect_globals.workqueues.idle == NULL)
+		goto alloc_idle_wq_failed;
+
+	smbdirect_globals.workqueues.refill = alloc_workqueue("smbdirect-refill",
+							      WQ_HIGHPRI |
+							      WQ_SYSFS |
+							      WQ_PERCPU |
+							      WQ_POWER_EFFICIENT,
+							      0);
+	if (smbdirect_globals.workqueues.refill == NULL)
+		goto alloc_refill_wq_failed;
+
+	smbdirect_globals.workqueues.immediate = alloc_workqueue("smbdirect-immediate",
+								 WQ_HIGHPRI |
+								 WQ_SYSFS |
+								 WQ_PERCPU |
+								 WQ_POWER_EFFICIENT,
+								 0);
+	if (smbdirect_globals.workqueues.immediate == NULL)
+		goto alloc_immediate_wq_failed;
+
+	smbdirect_globals.workqueues.cleanup = alloc_workqueue("smbdirect-cleanup",
+							       WQ_MEM_RECLAIM |
+							       WQ_HIGHPRI |
+							       WQ_SYSFS |
+							       WQ_PERCPU |
+							       WQ_POWER_EFFICIENT,
+							       0);
+	if (smbdirect_globals.workqueues.cleanup == NULL)
+		goto alloc_cleanup_wq_failed;
+
+	ret = smbdirect_devices_init();
+	if (ret)
+		goto devices_init_failed;
+
+	mutex_unlock(&smbdirect_globals.mutex);
+	pr_notice("subsystem loaded\n");
+	return 0;
+
+devices_init_failed:
+	destroy_workqueue(smbdirect_globals.workqueues.cleanup);
+alloc_cleanup_wq_failed:
+	destroy_workqueue(smbdirect_globals.workqueues.immediate);
+alloc_immediate_wq_failed:
+	destroy_workqueue(smbdirect_globals.workqueues.refill);
+alloc_refill_wq_failed:
+	destroy_workqueue(smbdirect_globals.workqueues.idle);
+alloc_idle_wq_failed:
+	destroy_workqueue(smbdirect_globals.workqueues.connect);
+alloc_connect_wq_failed:
+	destroy_workqueue(smbdirect_globals.workqueues.accept);
+alloc_accept_wq_failed:
+	mutex_unlock(&smbdirect_globals.mutex);
+	pr_crit("failed to loaded: %d (%1pe)\n",
+		ret, SMBDIRECT_DEBUG_ERR_PTR(ret));
+	return ret;
+}
+
+static __exit void smbdirect_module_exit(void)
+{
+	pr_notice("subsystem unloading...\n");
+	mutex_lock(&smbdirect_globals.mutex);
+
+	smbdirect_devices_exit();
+
+	destroy_workqueue(smbdirect_globals.workqueues.accept);
+	destroy_workqueue(smbdirect_globals.workqueues.connect);
+	destroy_workqueue(smbdirect_globals.workqueues.idle);
+	destroy_workqueue(smbdirect_globals.workqueues.refill);
+	destroy_workqueue(smbdirect_globals.workqueues.immediate);
+	destroy_workqueue(smbdirect_globals.workqueues.cleanup);
+
+	mutex_unlock(&smbdirect_globals.mutex);
+	pr_notice("subsystem unloaded\n");
+}
+
+module_init(smbdirect_module_init);
+module_exit(smbdirect_module_exit);
+
+MODULE_DESCRIPTION("smbdirect subsystem");
+MODULE_LICENSE("GPL");