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, 62 insertions, 0 deletions

diff --git a/fs/udf/lowlevel.c b/fs/udf/lowlevel.c
new file mode 100644
index 000000000..9d847a7a0
--- /dev/null
+++ b/fs/udf/lowlevel.c
@@ -0,0 +1,62 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * lowlevel.c
+ *
+ * PURPOSE
+ *  Low Level Device Routines for the UDF filesystem
+ *
+ * COPYRIGHT
+ *  (C) 1999-2001 Ben Fennema
+ *
+ * HISTORY
+ *
+ *  03/26/99 blf  Created.
+ */
+
+#include "udfdecl.h"
+
+#include <linux/blkdev.h>
+#include <linux/cdrom.h>
+#include <linux/uaccess.h>
+
+#include "udf_sb.h"
+
+unsigned int udf_get_last_session(struct super_block *sb)
+{
+	struct cdrom_device_info *cdi = disk_to_cdi(sb->s_bdev->bd_disk);
+	struct cdrom_multisession ms_info;
+
+	if (!cdi) {
+		udf_debug("CDROMMULTISESSION not supported.\n");
+		return 0;
+	}
+
+	ms_info.addr_format = CDROM_LBA;
+	if (cdrom_multisession(cdi, &ms_info) == 0) {
+		udf_debug("XA disk: %s, vol_desc_start=%d\n",
+			  ms_info.xa_flag ? "yes" : "no", ms_info.addr.lba);
+		if (ms_info.xa_flag) /* necessary for a valid ms_info.addr */
+			return ms_info.addr.lba;
+	}
+	return 0;
+}
+
+udf_pblk_t udf_get_last_block(struct super_block *sb)
+{
+	struct cdrom_device_info *cdi = disk_to_cdi(sb->s_bdev->bd_disk);
+	unsigned long lblock = 0;
+
+	/*
+	 * The cdrom layer call failed or returned obviously bogus value?
+	 * Try using the device size...
+	 */
+	if (!cdi || cdrom_get_last_written(cdi, &lblock) || lblock == 0) {
+		if (sb_bdev_nr_blocks(sb) > ~(udf_pblk_t)0)
+			return 0;
+		lblock = sb_bdev_nr_blocks(sb);
+	}
+
+	if (lblock)
+		return lblock - 1;
+	return 0;
+}