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, 50 insertions, 0 deletions

diff --git a/fs/hfs/sysdep.c b/fs/hfs/sysdep.c
new file mode 100644
index 000000000..ef54fc809
--- /dev/null
+++ b/fs/hfs/sysdep.c
@@ -0,0 +1,50 @@
+/*
+ *  linux/fs/hfs/sysdep.c
+ *
+ * Copyright (C) 1996  Paul H. Hargrove
+ * (C) 2003 Ardis Technologies <roman@ardistech.com>
+ * This file may be distributed under the terms of the GNU General Public License.
+ *
+ * This file contains the code to do various system dependent things.
+ */
+
+#include <linux/namei.h>
+#include "hfs_fs.h"
+
+/* dentry case-handling: just lowercase everything */
+
+static int hfs_revalidate_dentry(struct inode *dir, const struct qstr *name,
+				 struct dentry *dentry, unsigned int flags)
+{
+	struct inode *inode;
+	int diff;
+
+	if (flags & LOOKUP_RCU)
+		return -ECHILD;
+
+	inode = d_inode(dentry);
+	if(!inode)
+		return 1;
+
+	/* fix up inode on a timezone change */
+	diff = sys_tz.tz_minuteswest * 60 - HFS_I(inode)->tz_secondswest;
+	if (diff) {
+		struct timespec64 ts = inode_get_ctime(inode);
+
+		inode_set_ctime(inode, ts.tv_sec + diff, ts.tv_nsec);
+		ts = inode_get_atime(inode);
+		inode_set_atime(inode, ts.tv_sec + diff, ts.tv_nsec);
+		ts = inode_get_mtime(inode);
+		inode_set_mtime(inode, ts.tv_sec + diff, ts.tv_nsec);
+		HFS_I(inode)->tz_secondswest += diff;
+	}
+	return 1;
+}
+
+const struct dentry_operations hfs_dentry_operations =
+{
+	.d_revalidate	= hfs_revalidate_dentry,
+	.d_hash		= hfs_hash_dentry,
+	.d_compare	= hfs_compare_dentry,
+};
+