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, 50 insertions, 0 deletions

diff --git a/fs/ext2/xattr_user.c b/fs/ext2/xattr_user.c
new file mode 100644
index 000000000..dd1507231
--- /dev/null
+++ b/fs/ext2/xattr_user.c
@@ -0,0 +1,50 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * linux/fs/ext2/xattr_user.c
+ * Handler for extended user attributes.
+ *
+ * Copyright (C) 2001 by Andreas Gruenbacher, <a.gruenbacher@computer.org>
+ */
+
+#include <linux/init.h>
+#include <linux/string.h>
+#include "ext2.h"
+#include "xattr.h"
+
+static bool
+ext2_xattr_user_list(struct dentry *dentry)
+{
+	return test_opt(dentry->d_sb, XATTR_USER);
+}
+
+static int
+ext2_xattr_user_get(const struct xattr_handler *handler,
+		    struct dentry *unused, struct inode *inode,
+		    const char *name, void *buffer, size_t size)
+{
+	if (!test_opt(inode->i_sb, XATTR_USER))
+		return -EOPNOTSUPP;
+	return ext2_xattr_get(inode, EXT2_XATTR_INDEX_USER,
+			      name, buffer, size);
+}
+
+static int
+ext2_xattr_user_set(const struct xattr_handler *handler,
+		    struct mnt_idmap *idmap,
+		    struct dentry *unused, struct inode *inode,
+		    const char *name, const void *value,
+		    size_t size, int flags)
+{
+	if (!test_opt(inode->i_sb, XATTR_USER))
+		return -EOPNOTSUPP;
+
+	return ext2_xattr_set(inode, EXT2_XATTR_INDEX_USER,
+			      name, value, size, flags);
+}
+
+const struct xattr_handler ext2_xattr_user_handler = {
+	.prefix	= XATTR_USER_PREFIX,
+	.list	= ext2_xattr_user_list,
+	.get	= ext2_xattr_user_get,
+	.set	= ext2_xattr_user_set,
+};