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, 36 insertions, 0 deletions

diff --git a/drivers/media/dvb-frontends/nxt6000.h b/drivers/media/dvb-frontends/nxt6000.h
new file mode 100644
index 000000000..28d965e53
--- /dev/null
+++ b/drivers/media/dvb-frontends/nxt6000.h
@@ -0,0 +1,36 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+	NxtWave Communications - NXT6000 demodulator driver
+
+    Copyright (C) 2002-2003 Florian Schirmer <jolt@tuxbox.org>
+    Copyright (C) 2003 Paul Andreassen <paul@andreassen.com.au>
+
+*/
+
+#ifndef NXT6000_H
+#define NXT6000_H
+
+#include <linux/dvb/frontend.h>
+
+struct nxt6000_config
+{
+	/* the demodulator's i2c address */
+	u8 demod_address;
+
+	/* should clock inversion be used? */
+	u8 clock_inversion:1;
+};
+
+#if IS_REACHABLE(CONFIG_DVB_NXT6000)
+extern struct dvb_frontend* nxt6000_attach(const struct nxt6000_config* config,
+					   struct i2c_adapter* i2c);
+#else
+static inline struct dvb_frontend* nxt6000_attach(const struct nxt6000_config* config,
+					   struct i2c_adapter* i2c)
+{
+	printk(KERN_WARNING "%s: driver disabled by Kconfig\n", __func__);
+	return NULL;
+}
+#endif // CONFIG_DVB_NXT6000
+
+#endif // NXT6000_H