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, 25 insertions, 0 deletions

diff --git a/lib/notifier-error-inject.h b/lib/notifier-error-inject.h
new file mode 100644
index 000000000..fafff5f2a
--- /dev/null
+++ b/lib/notifier-error-inject.h
@@ -0,0 +1,25 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#include <linux/atomic.h>
+#include <linux/debugfs.h>
+#include <linux/notifier.h>
+
+struct notifier_err_inject_action {
+	unsigned long val;
+	int error;
+	const char *name;
+};
+
+#define NOTIFIER_ERR_INJECT_ACTION(action)	\
+	.name = #action, .val = (action),
+
+struct notifier_err_inject {
+	struct notifier_block nb;
+	struct notifier_err_inject_action actions[];
+	/* The last slot must be terminated with zero sentinel */
+};
+
+extern struct dentry *notifier_err_inject_dir;
+
+extern struct dentry *notifier_err_inject_init(const char *name,
+		struct dentry *parent, struct notifier_err_inject *err_inject,
+		int priority);