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, 66 insertions, 0 deletions

diff --git a/fs/ext4/xattr_security.c b/fs/ext4/xattr_security.c
new file mode 100644
index 000000000..776cf11d2
--- /dev/null
+++ b/fs/ext4/xattr_security.c
@@ -0,0 +1,66 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * linux/fs/ext4/xattr_security.c
+ * Handler for storing security labels as extended attributes.
+ */
+
+#include <linux/string.h>
+#include <linux/fs.h>
+#include <linux/security.h>
+#include <linux/slab.h>
+#include "ext4_jbd2.h"
+#include "ext4.h"
+#include "xattr.h"
+
+static int
+ext4_xattr_security_get(const struct xattr_handler *handler,
+			struct dentry *unused, struct inode *inode,
+			const char *name, void *buffer, size_t size)
+{
+	return ext4_xattr_get(inode, EXT4_XATTR_INDEX_SECURITY,
+			      name, buffer, size);
+}
+
+static int
+ext4_xattr_security_set(const struct xattr_handler *handler,
+			struct mnt_idmap *idmap,
+			struct dentry *unused, struct inode *inode,
+			const char *name, const void *value,
+			size_t size, int flags)
+{
+	return ext4_xattr_set(inode, EXT4_XATTR_INDEX_SECURITY,
+			      name, value, size, flags);
+}
+
+static int
+ext4_initxattrs(struct inode *inode, const struct xattr *xattr_array,
+		void *fs_info)
+{
+	const struct xattr *xattr;
+	handle_t *handle = fs_info;
+	int err = 0;
+
+	for (xattr = xattr_array; xattr->name != NULL; xattr++) {
+		err = ext4_xattr_set_handle(handle, inode,
+					    EXT4_XATTR_INDEX_SECURITY,
+					    xattr->name, xattr->value,
+					    xattr->value_len, XATTR_CREATE);
+		if (err < 0)
+			break;
+	}
+	return err;
+}
+
+int
+ext4_init_security(handle_t *handle, struct inode *inode, struct inode *dir,
+		   const struct qstr *qstr)
+{
+	return security_inode_init_security(inode, dir, qstr,
+					    &ext4_initxattrs, handle);
+}
+
+const struct xattr_handler ext4_xattr_security_handler = {
+	.prefix	= XATTR_SECURITY_PREFIX,
+	.get	= ext4_xattr_security_get,
+	.set	= ext4_xattr_security_set,
+};