bpf: mark a NULL kfunc argument precisegrafted

check_kfunc_arg() allows bpf_register_is_null() for nullable arguments
w/o marking the underlying scalar register precise. Hence a checkpoint
created on such a path would prune against arbitrary scalar value.

Fixes: 3bda08b63670 ("bpf: Allow NULL buffers in bpf_dynptr_slice(_rw)")
Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20260904-register-is-null-precise-fixes-v1-5-0f5a360ff15d@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 68 insertions, 0 deletions

diff --git a/io_uring/statx.c b/io_uring/statx.c
new file mode 100644
index 000000000..7bcae4a6c
--- /dev/null
+++ b/io_uring/statx.c
@@ -0,0 +1,68 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/kernel.h>
+#include <linux/errno.h>
+#include <linux/file.h>
+#include <linux/io_uring.h>
+
+#include <uapi/linux/io_uring.h>
+
+#include "../fs/internal.h"
+
+#include "io_uring.h"
+#include "statx.h"
+
+struct io_statx {
+	struct file			*file;
+	int				dfd;
+	unsigned int			mask;
+	unsigned int			flags;
+	struct delayed_filename		filename;
+	struct statx __user		*buffer;
+};
+
+int io_statx_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
+{
+	struct io_statx *sx = io_kiocb_to_cmd(req, struct io_statx);
+	const char __user *path;
+	int ret;
+
+	if (sqe->buf_index || sqe->splice_fd_in)
+		return -EINVAL;
+	if (req->flags & REQ_F_FIXED_FILE)
+		return -EBADF;
+
+	sx->dfd = READ_ONCE(sqe->fd);
+	sx->mask = READ_ONCE(sqe->len);
+	path = u64_to_user_ptr(READ_ONCE(sqe->addr));
+	sx->buffer = u64_to_user_ptr(READ_ONCE(sqe->addr2));
+	sx->flags = READ_ONCE(sqe->statx_flags);
+
+	ret = delayed_getname_uflags(&sx->filename, path, sx->flags);
+
+	if (unlikely(ret))
+		return ret;
+
+	req->flags |= REQ_F_NEED_CLEANUP;
+	req->flags |= REQ_F_FORCE_ASYNC;
+	return 0;
+}
+
+int io_statx(struct io_kiocb *req, unsigned int issue_flags)
+{
+	struct io_statx *sx = io_kiocb_to_cmd(req, struct io_statx);
+	CLASS(filename_complete_delayed, name)(&sx->filename);
+	int ret;
+
+	WARN_ON_ONCE(issue_flags & IO_URING_F_NONBLOCK);
+
+	ret = do_statx(sx->dfd, name, sx->flags, sx->mask, sx->buffer);
+	io_req_set_res(req, ret, 0);
+	return IOU_COMPLETE;
+}
+
+void io_statx_cleanup(struct io_kiocb *req)
+{
+	struct io_statx *sx = io_kiocb_to_cmd(req, struct io_statx);
+
+	dismiss_delayed_filename(&sx->filename);
+}