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, 64 insertions, 0 deletions

diff --git a/fs/proc/devices.c b/fs/proc/devices.c
new file mode 100644
index 000000000..fe7bfcb7d
--- /dev/null
+++ b/fs/proc/devices.c
@@ -0,0 +1,64 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/fs.h>
+#include <linux/init.h>
+#include <linux/proc_fs.h>
+#include <linux/seq_file.h>
+#include <linux/blkdev.h>
+#include "internal.h"
+
+static int devinfo_show(struct seq_file *f, void *v)
+{
+	int i = *(loff_t *) v;
+
+	if (i < CHRDEV_MAJOR_MAX) {
+		if (i == 0)
+			seq_puts(f, "Character devices:\n");
+		chrdev_show(f, i);
+	}
+#ifdef CONFIG_BLOCK
+	else {
+		i -= CHRDEV_MAJOR_MAX;
+		if (i == 0)
+			seq_puts(f, "\nBlock devices:\n");
+		blkdev_show(f, i);
+	}
+#endif
+	return 0;
+}
+
+static void *devinfo_start(struct seq_file *f, loff_t *pos)
+{
+	if (*pos < (BLKDEV_MAJOR_MAX + CHRDEV_MAJOR_MAX))
+		return pos;
+	return NULL;
+}
+
+static void *devinfo_next(struct seq_file *f, void *v, loff_t *pos)
+{
+	(*pos)++;
+	if (*pos >= (BLKDEV_MAJOR_MAX + CHRDEV_MAJOR_MAX))
+		return NULL;
+	return pos;
+}
+
+static void devinfo_stop(struct seq_file *f, void *v)
+{
+	/* Nothing to do */
+}
+
+static const struct seq_operations devinfo_ops = {
+	.start = devinfo_start,
+	.next  = devinfo_next,
+	.stop  = devinfo_stop,
+	.show  = devinfo_show
+};
+
+static int __init proc_devices_init(void)
+{
+	struct proc_dir_entry *pde;
+
+	pde = proc_create_seq("devices", 0, NULL, &devinfo_ops);
+	pde_make_permanent(pde);
+	return 0;
+}
+fs_initcall(proc_devices_init);