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, 116 insertions, 0 deletions

diff --git a/fs/afs/xdr_fs.h b/fs/afs/xdr_fs.h
new file mode 100644
index 000000000..cc5f143d2
--- /dev/null
+++ b/fs/afs/xdr_fs.h
@@ -0,0 +1,116 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/* AFS fileserver XDR types
+ *
+ * Copyright (C) 2018 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ */
+
+#ifndef XDR_FS_H
+#define XDR_FS_H
+
+struct afs_xdr_AFSFetchStatus {
+	__be32	if_version;
+#define AFS_FSTATUS_VERSION	1
+	__be32	type;
+	__be32	nlink;
+	__be32	size_lo;
+	__be32	data_version_lo;
+	__be32	author;
+	__be32	owner;
+	__be32	caller_access;
+	__be32	anon_access;
+	__be32	mode;
+	__be32	parent_vnode;
+	__be32	parent_unique;
+	__be32	seg_size;
+	__be32	mtime_client;
+	__be32	mtime_server;
+	__be32	group;
+	__be32	sync_counter;
+	__be32	data_version_hi;
+	__be32	lock_count;
+	__be32	size_hi;
+	__be32	abort_code;
+} __packed;
+
+#define AFS_DIR_HASHTBL_SIZE	128
+#define AFS_DIR_DIRENT_SIZE	32
+#define AFS_DIR_SLOTS_PER_BLOCK	64
+#define AFS_DIR_BLOCK_SIZE	2048
+#define AFS_DIR_BLOCKS_PER_PAGE	(PAGE_SIZE / AFS_DIR_BLOCK_SIZE)
+#define AFS_DIR_MAX_SLOTS	65536
+#define AFS_DIR_BLOCKS_WITH_CTR	128
+#define AFS_DIR_MAX_BLOCKS	1023
+#define AFS_DIR_RESV_BLOCKS	1
+#define AFS_DIR_RESV_BLOCKS0	13
+
+/*
+ * Directory entry structure.
+ */
+union afs_xdr_dirent {
+	struct {
+		u8		valid;
+		u8		unused[1];
+		__be16		hash_next;
+		__be32		vnode;
+		__be32		unique;
+		u8		name[];
+		/* When determining the number of dirent slots needed to
+		 * represent a directory entry, name should be assumed to be 16
+		 * bytes, due to a now-standardised (mis)calculation, but it is
+		 * in fact 20 bytes in size.  afs_dir_calc_slots() should be
+		 * used for this.
+		 *
+		 * For names longer than (16 or) 20 bytes, extra slots should
+		 * be annexed to this one using the extended_name format.
+		 */
+	} u;
+	u8			extended_name[32];
+} __packed;
+
+/*
+ * Directory block header (one at the beginning of every 2048-byte block).
+ */
+struct afs_xdr_dir_hdr {
+	__be16		npages;
+	__be16		magic;
+#define AFS_DIR_MAGIC htons(1234)
+	u8		reserved;
+	u8		bitmap[8];
+	u8		pad[19];
+} __packed;
+
+/*
+ * Directory block layout
+ */
+union afs_xdr_dir_block {
+	struct afs_xdr_dir_hdr		hdr;
+
+	struct {
+		struct afs_xdr_dir_hdr	hdr;
+		u8			alloc_ctrs[AFS_DIR_BLOCKS_WITH_CTR];
+		__be16			hashtable[AFS_DIR_HASHTBL_SIZE];
+	} meta;
+
+	union afs_xdr_dirent	dirents[AFS_DIR_SLOTS_PER_BLOCK];
+} __packed;
+
+/*
+ * Directory layout on a linux VM page.
+ */
+struct afs_xdr_dir_page {
+	union afs_xdr_dir_block	blocks[AFS_DIR_BLOCKS_PER_PAGE];
+};
+
+/*
+ * Calculate the number of dirent slots required for any given name length.
+ * The calculation is made assuming the part of the name in the first slot is
+ * 16 bytes, rather than 20, but this miscalculation is now standardised.
+ */
+static inline unsigned int afs_dir_calc_slots(size_t name_len)
+{
+	name_len++; /* NUL-terminated */
+	return 1 + ((name_len + 15) / AFS_DIR_DIRENT_SIZE);
+}
+
+#endif /* XDR_FS_H */