io_uring: don't re-import iovecs from callbacks

We can't re-import or modify iterators from iocb callbacks, it's not
safe as it might be reverted and/or reexpanded while unwinding stack.
It's also not safe to resubmit as io-wq thread will race with stack
undwinding for the iterator and other data.

Disallow resubmission from callbacks, it can fail some cases that were
handled before, but the possibility of such a failure was a part of the
API from the beginning and so it should be fine.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

fs/io_uring.c

@@ -2579,45 +2579,6 @@ static void io_complete_rw_common(struct kiocb *kiocb, long res,
 #ifdef CONFIG_BLOCK
 static bool io_resubmit_prep(struct io_kiocb *req, int error)
 {
-	struct iovec inline_vecs[UIO_FASTIOV], *iovec = inline_vecs;
-	ssize_t ret = -ECANCELED;
-	struct iov_iter iter;
-	int rw;
-
-	if (error) {
-		ret = error;
-		goto end_req;
-	}
-
-	switch (req->opcode) {
-	case IORING_OP_READV:
-	case IORING_OP_READ_FIXED:
-	case IORING_OP_READ:
-		rw = READ;
-		break;
-	case IORING_OP_WRITEV:
-	case IORING_OP_WRITE_FIXED:
-	case IORING_OP_WRITE:
-		rw = WRITE;
-		break;
-	default:
-		printk_once(KERN_WARNING "io_uring: bad opcode in resubmit %d\n",
-				req->opcode);
-		goto end_req;
-	}
-
-	if (!req->async_data) {
-		ret = io_import_iovec(rw, req, &iovec, &iter, false);
-		if (ret < 0)
-			goto end_req;
-		ret = io_setup_async_rw(req, iovec, inline_vecs, &iter, false);
-		if (!ret)
-			return true;
-		kfree(iovec);
-	} else {
-		return true;
-	}
-end_req:
 	req_set_fail_links(req);
 	return false;
 }