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, 38 insertions, 0 deletions

diff --git a/fs/hfsplus/xattr_user.c b/fs/hfsplus/xattr_user.c
new file mode 100644
index 000000000..6464b6c3d
--- /dev/null
+++ b/fs/hfsplus/xattr_user.c
@@ -0,0 +1,38 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * linux/fs/hfsplus/xattr_user.c
+ *
+ * Vyacheslav Dubeyko <slava@dubeyko.com>
+ *
+ * Handler for user extended attributes.
+ */
+
+#include <linux/nls.h>
+
+#include "hfsplus_fs.h"
+#include "xattr.h"
+
+static int hfsplus_user_getxattr(const struct xattr_handler *handler,
+				 struct dentry *unused, struct inode *inode,
+				 const char *name, void *buffer, size_t size)
+{
+
+	return hfsplus_getxattr(inode, name, buffer, size,
+				XATTR_USER_PREFIX, XATTR_USER_PREFIX_LEN);
+}
+
+static int hfsplus_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 hfsplus_setxattr(inode, name, buffer, size, flags,
+				XATTR_USER_PREFIX, XATTR_USER_PREFIX_LEN);
+}
+
+const struct xattr_handler hfsplus_xattr_user_handler = {
+	.prefix	= XATTR_USER_PREFIX,
+	.get	= hfsplus_user_getxattr,
+	.set	= hfsplus_user_setxattr,
+};