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, 55 insertions, 0 deletions

diff --git a/fs/befs/inode.c b/fs/befs/inode.c
new file mode 100644
index 000000000..791b46a6f
--- /dev/null
+++ b/fs/befs/inode.c
@@ -0,0 +1,55 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * inode.c
+ *
+ * Copyright (C) 2001 Will Dyson <will_dyson@pobox.com>
+ */
+
+#include <linux/fs.h>
+
+#include "befs.h"
+#include "inode.h"
+
+/*
+ * Validates the correctness of the befs inode
+ * Returns BEFS_OK if the inode should be used, otherwise
+ * returns BEFS_BAD_INODE
+ */
+int
+befs_check_inode(struct super_block *sb, befs_inode *raw_inode,
+		 befs_blocknr_t inode)
+{
+	u32 magic1 = fs32_to_cpu(sb, raw_inode->magic1);
+	befs_inode_addr ino_num = fsrun_to_cpu(sb, raw_inode->inode_num);
+	u32 flags = fs32_to_cpu(sb, raw_inode->flags);
+
+	/* check magic header. */
+	if (magic1 != BEFS_INODE_MAGIC1) {
+		befs_error(sb,
+			   "Inode has a bad magic header - inode = %lu",
+			   (unsigned long)inode);
+		return BEFS_BAD_INODE;
+	}
+
+	/*
+	 * Sanity check2: inodes store their own block address. Check it.
+	 */
+	if (inode != iaddr2blockno(sb, &ino_num)) {
+		befs_error(sb, "inode blocknr field disagrees with vfs "
+			   "VFS: %lu, Inode %lu", (unsigned long)
+			   inode, (unsigned long)iaddr2blockno(sb, &ino_num));
+		return BEFS_BAD_INODE;
+	}
+
+	/*
+	 * check flag
+	 */
+
+	if (!(flags & BEFS_INODE_IN_USE)) {
+		befs_error(sb, "inode is not used - inode = %lu",
+			   (unsigned long)inode);
+		return BEFS_BAD_INODE;
+	}
+
+	return BEFS_OK;
+}