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, 47 insertions, 0 deletions

diff --git a/fs/netfs/fscache_proc.c b/fs/netfs/fscache_proc.c
new file mode 100644
index 000000000..874d951bc
--- /dev/null
+++ b/fs/netfs/fscache_proc.c
@@ -0,0 +1,47 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/* FS-Cache statistics viewing interface
+ *
+ * Copyright (C) 2021 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ */
+
+#define FSCACHE_DEBUG_LEVEL CACHE
+#include <linux/module.h>
+#include <linux/proc_fs.h>
+#include <linux/seq_file.h>
+#include "internal.h"
+
+/*
+ * Add files to /proc/fs/netfs/.
+ */
+int __init fscache_proc_init(void)
+{
+	if (!proc_symlink("fs/fscache", NULL, "netfs"))
+		goto error_sym;
+
+	if (!proc_create_seq("fs/netfs/caches", S_IFREG | 0444, NULL,
+			     &fscache_caches_seq_ops))
+		goto error;
+
+	if (!proc_create_seq("fs/netfs/volumes", S_IFREG | 0444, NULL,
+			     &fscache_volumes_seq_ops))
+		goto error;
+
+	if (!proc_create_seq("fs/netfs/cookies", S_IFREG | 0444, NULL,
+			     &fscache_cookies_seq_ops))
+		goto error;
+	return 0;
+
+error:
+	remove_proc_entry("fs/fscache", NULL);
+error_sym:
+	return -ENOMEM;
+}
+
+/*
+ * Clean up the /proc/fs/fscache symlink.
+ */
+void fscache_proc_cleanup(void)
+{
+	remove_proc_subtree("fs/fscache", NULL);
+}