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, 100 insertions, 0 deletions

diff --git a/fs/xfs/scrub/rgsuper.c b/fs/xfs/scrub/rgsuper.c
new file mode 100644
index 000000000..2bd2c0351
--- /dev/null
+++ b/fs/xfs/scrub/rgsuper.c
@@ -0,0 +1,100 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (c) 2022-2024 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_rtgroup.h"
+#include "xfs_log_format.h"
+#include "xfs_trans.h"
+#include "xfs_sb.h"
+#include "xfs_rmap.h"
+#include "scrub/scrub.h"
+#include "scrub/common.h"
+#include "scrub/repair.h"
+
+/* Set us up with a transaction and an empty context. */
+int
+xchk_setup_rgsuperblock(
+	struct xfs_scrub	*sc)
+{
+	if (xchk_need_intent_drain(sc))
+		xchk_fsgates_enable(sc, XCHK_FSGATES_DRAIN);
+	return xchk_trans_alloc(sc, 0);
+}
+
+/* Cross-reference with the other rt metadata. */
+STATIC void
+xchk_rgsuperblock_xref(
+	struct xfs_scrub	*sc)
+{
+	if (sc->sm->sm_flags & XFS_SCRUB_OFLAG_CORRUPT)
+		return;
+
+	xchk_xref_is_used_rt_space(sc, xfs_rgbno_to_rtb(sc->sr.rtg, 0), 1);
+	xchk_xref_is_only_rt_owned_by(sc, 0, 1, &XFS_RMAP_OINFO_FS);
+}
+
+int
+xchk_rgsuperblock(
+	struct xfs_scrub	*sc)
+{
+	xfs_rgnumber_t		rgno = sc->sm->sm_agno;
+	unsigned int		flags;
+	int			error;
+
+	/*
+	 * Only rtgroup 0 has a superblock.  We may someday want to use higher
+	 * rgno for other functions, similar to what we do with the primary
+	 * super scrub function.
+	 */
+	if (rgno != 0)
+		return -ENOENT;
+
+	/*
+	 * Grab an active reference to the rtgroup structure.  If we can't get
+	 * it, we're racing with something that's tearing down the group, so
+	 * signal that the group no longer exists.  Take the rtbitmap in shared
+	 * mode so that the group can't change while we're doing things.
+	 */
+	error = xchk_rtgroup_init_existing(sc, rgno, &sc->sr);
+	if (!xchk_xref_process_error(sc, 0, 0, &error))
+		return error;
+
+	if (xfs_has_rtrmapbt(sc->mp))
+		flags = XFS_RTGLOCK_BITMAP | XFS_RTGLOCK_RMAP;
+	else
+		flags = XFS_RTGLOCK_BITMAP_SHARED;
+
+	error = xchk_rtgroup_lock(sc, &sc->sr, flags);
+	if (error)
+		return error;
+
+	/*
+	 * Since we already validated the rt superblock at mount time, we don't
+	 * need to check its contents again.  All we need is to cross-reference.
+	 */
+	xchk_rgsuperblock_xref(sc);
+	return 0;
+}
+
+#ifdef CONFIG_XFS_ONLINE_REPAIR
+int
+xrep_rgsuperblock(
+	struct xfs_scrub	*sc)
+{
+	struct xfs_buf		*sb_bp;
+
+	ASSERT(rtg_rgno(sc->sr.rtg) == 0);
+
+	sb_bp = xfs_trans_getsb(sc->tp);
+	xfs_log_sb(sc->tp);
+	xfs_log_rtsb(sc->tp, sb_bp);
+	return 0;
+}
+#endif /* CONFIG_XFS_ONLINE_REPAIR */