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, 75 insertions, 0 deletions

diff --git a/fs/affs/symlink.c b/fs/affs/symlink.c
new file mode 100644
index 000000000..4994abb97
--- /dev/null
+++ b/fs/affs/symlink.c
@@ -0,0 +1,75 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ *  linux/fs/affs/symlink.c
+ *
+ *  1995  Hans-Joachim Widmaier - Modified for affs.
+ *
+ *  Copyright (C) 1991, 1992  Linus Torvalds
+ *
+ *  affs symlink handling code
+ */
+
+#include "affs.h"
+
+static int affs_symlink_read_folio(struct file *file, struct folio *folio)
+{
+	struct buffer_head *bh;
+	struct inode *inode = folio->mapping->host;
+	char *link = folio_address(folio);
+	struct slink_front *lf;
+	int			 i, j;
+	char			 c;
+	char			 lc;
+
+	pr_debug("get_link(ino=%llu)\n", inode->i_ino);
+
+	bh = affs_bread(inode->i_sb, inode->i_ino);
+	if (!bh)
+		goto fail;
+	i  = 0;
+	j  = 0;
+	lf = (struct slink_front *)bh->b_data;
+	lc = 0;
+
+	if (strchr(lf->symname,':')) {	/* Handle assign or volume name */
+		struct affs_sb_info *sbi = AFFS_SB(inode->i_sb);
+		char *pf;
+		spin_lock(&sbi->symlink_lock);
+		pf = sbi->s_prefix ? sbi->s_prefix : "/";
+		while (i < 1023 && (c = pf[i]))
+			link[i++] = c;
+		spin_unlock(&sbi->symlink_lock);
+		while (i < 1023 && lf->symname[j] != ':')
+			link[i++] = lf->symname[j++];
+		if (i < 1023)
+			link[i++] = '/';
+		j++;
+		lc = '/';
+	}
+	while (i < 1023 && (c = lf->symname[j])) {
+		if (c == '/' && lc == '/' && i < 1020) {	/* parent dir */
+			link[i++] = '.';
+			link[i++] = '.';
+		}
+		link[i++] = c;
+		lc = c;
+		j++;
+	}
+	link[i] = '\0';
+	affs_brelse(bh);
+	folio_mark_uptodate(folio);
+	folio_unlock(folio);
+	return 0;
+fail:
+	folio_unlock(folio);
+	return -EIO;
+}
+
+const struct address_space_operations affs_symlink_aops = {
+	.read_folio	= affs_symlink_read_folio,
+};
+
+const struct inode_operations affs_symlink_inode_operations = {
+	.get_link	= page_get_link,
+	.setattr	= affs_setattr,
+};