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, 195 insertions, 0 deletions

diff --git a/fs/xfs/scrub/alloc.c b/fs/xfs/scrub/alloc.c
new file mode 100644
index 000000000..c666be69f
--- /dev/null
+++ b/fs/xfs/scrub/alloc.c
@@ -0,0 +1,195 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (C) 2017-2023 Oracle.  All Rights Reserved.
+ * Author: Darrick J. Wong <djwong@kernel.org>
+ */
+#include "xfs_platform.h"
+#include "xfs_fs.h"
+#include "xfs_shared.h"
+#include "xfs_format.h"
+#include "xfs_trans_resv.h"
+#include "xfs_mount.h"
+#include "xfs_log_format.h"
+#include "xfs_trans.h"
+#include "xfs_btree.h"
+#include "xfs_alloc.h"
+#include "xfs_rmap.h"
+#include "xfs_ag.h"
+#include "scrub/scrub.h"
+#include "scrub/common.h"
+#include "scrub/btree.h"
+#include "scrub/repair.h"
+
+/*
+ * Set us up to scrub free space btrees.
+ */
+int
+xchk_setup_ag_allocbt(
+	struct xfs_scrub	*sc)
+{
+	int			error;
+
+	if (xchk_need_intent_drain(sc))
+		xchk_fsgates_enable(sc, XCHK_FSGATES_DRAIN);
+
+	error = xchk_setup_ag_btree(sc, false);
+	if (error)
+		return error;
+
+	if (xchk_could_repair(sc))
+		return xrep_setup_ag_allocbt(sc);
+
+	return 0;
+}
+
+/* Free space btree scrubber. */
+
+struct xchk_alloc {
+	/* Previous free space extent. */
+	struct xfs_alloc_rec_incore	prev;
+};
+
+/*
+ * Ensure there's a corresponding cntbt/bnobt record matching this
+ * bnobt/cntbt record, respectively.
+ */
+STATIC void
+xchk_allocbt_xref_other(
+	struct xfs_scrub	*sc,
+	xfs_agblock_t		agbno,
+	xfs_extlen_t		len)
+{
+	struct xfs_btree_cur	**pcur;
+	xfs_agblock_t		fbno;
+	xfs_extlen_t		flen;
+	int			has_otherrec;
+	int			error;
+
+	if (sc->sm->sm_type == XFS_SCRUB_TYPE_BNOBT)
+		pcur = &sc->sa.cnt_cur;
+	else
+		pcur = &sc->sa.bno_cur;
+	if (!*pcur || xchk_skip_xref(sc->sm))
+		return;
+
+	error = xfs_alloc_lookup_le(*pcur, agbno, len, &has_otherrec);
+	if (!xchk_should_check_xref(sc, &error, pcur))
+		return;
+	if (!has_otherrec) {
+		xchk_btree_xref_set_corrupt(sc, *pcur, 0);
+		return;
+	}
+
+	error = xfs_alloc_get_rec(*pcur, &fbno, &flen, &has_otherrec);
+	if (!xchk_should_check_xref(sc, &error, pcur))
+		return;
+	if (!has_otherrec) {
+		xchk_btree_xref_set_corrupt(sc, *pcur, 0);
+		return;
+	}
+
+	if (fbno != agbno || flen != len)
+		xchk_btree_xref_set_corrupt(sc, *pcur, 0);
+}
+
+/* Cross-reference with the other btrees. */
+STATIC void
+xchk_allocbt_xref(
+	struct xfs_scrub	*sc,
+	const struct xfs_alloc_rec_incore *irec)
+{
+	xfs_agblock_t		agbno = irec->ar_startblock;
+	xfs_extlen_t		len = irec->ar_blockcount;
+
+	if (sc->sm->sm_flags & XFS_SCRUB_OFLAG_CORRUPT)
+		return;
+
+	xchk_allocbt_xref_other(sc, agbno, len);
+	xchk_xref_is_not_inode_chunk(sc, agbno, len);
+	xchk_xref_has_no_owner(sc, agbno, len);
+	xchk_xref_is_not_shared(sc, agbno, len);
+	xchk_xref_is_not_cow_staging(sc, agbno, len);
+}
+
+/* Flag failures for records that could be merged. */
+STATIC void
+xchk_allocbt_mergeable(
+	struct xchk_btree	*bs,
+	struct xchk_alloc	*ca,
+	const struct xfs_alloc_rec_incore *irec)
+{
+	if (bs->sc->sm->sm_flags & XFS_SCRUB_OFLAG_CORRUPT)
+		return;
+
+	if (ca->prev.ar_blockcount > 0 &&
+	    ca->prev.ar_startblock + ca->prev.ar_blockcount == irec->ar_startblock &&
+	    ca->prev.ar_blockcount + irec->ar_blockcount < (uint32_t)~0U)
+		xchk_btree_set_corrupt(bs->sc, bs->cur, 0);
+
+	memcpy(&ca->prev, irec, sizeof(*irec));
+}
+
+/* Scrub a bnobt/cntbt record. */
+STATIC int
+xchk_allocbt_rec(
+	struct xchk_btree		*bs,
+	const union xfs_btree_rec	*rec)
+{
+	struct xfs_alloc_rec_incore	irec;
+	struct xchk_alloc		*ca = bs->private;
+
+	xfs_alloc_btrec_to_irec(rec, &irec);
+	if (xfs_alloc_check_irec(to_perag(bs->cur->bc_group), &irec) != NULL) {
+		xchk_btree_set_corrupt(bs->sc, bs->cur, 0);
+		return 0;
+	}
+
+	if (bs->sc->sm->sm_type == XFS_SCRUB_TYPE_BNOBT)
+		xchk_allocbt_mergeable(bs, ca, &irec);
+	xchk_allocbt_xref(bs->sc, &irec);
+
+	return 0;
+}
+
+/* Scrub one of the freespace btrees for some AG. */
+int
+xchk_allocbt(
+	struct xfs_scrub	*sc)
+{
+	struct xchk_alloc	ca = { };
+	struct xfs_btree_cur	*cur;
+
+	switch (sc->sm->sm_type) {
+	case XFS_SCRUB_TYPE_BNOBT:
+		cur = sc->sa.bno_cur;
+		break;
+	case XFS_SCRUB_TYPE_CNTBT:
+		cur = sc->sa.cnt_cur;
+		break;
+	default:
+		ASSERT(0);
+		return -EIO;
+	}
+
+	return xchk_btree(sc, cur, xchk_allocbt_rec, &XFS_RMAP_OINFO_AG, &ca);
+}
+
+/* xref check that the extent is not free */
+void
+xchk_xref_is_used_space(
+	struct xfs_scrub	*sc,
+	xfs_agblock_t		agbno,
+	xfs_extlen_t		len)
+{
+	enum xbtree_recpacking	outcome;
+	int			error;
+
+	if (!sc->sa.bno_cur || xchk_skip_xref(sc->sm))
+		return;
+
+	error = xfs_alloc_has_records(sc->sa.bno_cur, agbno, len, &outcome);
+	if (!xchk_should_check_xref(sc, &error, &sc->sa.bno_cur))
+		return;
+	if (outcome != XBTREE_RECPACKING_EMPTY)
+		xchk_btree_xref_set_corrupt(sc, sc->sa.bno_cur, 0);
+}