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, 41 insertions, 0 deletions

diff --git a/fs/jffs2/xattr_user.c b/fs/jffs2/xattr_user.c
new file mode 100644
index 000000000..f64edce49
--- /dev/null
+++ b/fs/jffs2/xattr_user.c
@@ -0,0 +1,41 @@
+/*
+ * JFFS2 -- Journalling Flash File System, Version 2.
+ *
+ * Copyright © 2006  NEC Corporation
+ *
+ * Created by KaiGai Kohei <kaigai@ak.jp.nec.com>
+ *
+ * For licensing information, see the file 'LICENCE' in this directory.
+ *
+ */
+
+#include <linux/kernel.h>
+#include <linux/fs.h>
+#include <linux/jffs2.h>
+#include <linux/xattr.h>
+#include <linux/mtd/mtd.h>
+#include "nodelist.h"
+
+static int jffs2_user_getxattr(const struct xattr_handler *handler,
+			       struct dentry *unused, struct inode *inode,
+			       const char *name, void *buffer, size_t size)
+{
+	return do_jffs2_getxattr(inode, JFFS2_XPREFIX_USER,
+				 name, buffer, size);
+}
+
+static int jffs2_user_setxattr(const struct xattr_handler *handler,
+			       struct mnt_idmap *idmap,
+			       struct dentry *unused, struct inode *inode,
+			       const char *name, const void *buffer,
+			       size_t size, int flags)
+{
+	return do_jffs2_setxattr(inode, JFFS2_XPREFIX_USER,
+				 name, buffer, size, flags);
+}
+
+const struct xattr_handler jffs2_user_xattr_handler = {
+	.prefix = XATTR_USER_PREFIX,
+	.set = jffs2_user_setxattr,
+	.get = jffs2_user_getxattr
+};