io_uring: check reserved fields for send/sendmsg

We should check unused fields for non-zero and -EINVAL if they are set,
making it consistent with other opcodes.

Fixes: 0fa03c6 ("io_uring: add support for sendmsg()")
Signed-off-by: Jens Axboe <axboe@kernel.dk>

fs/io_uring.c

@@ -5207,6 +5207,8 @@ static int io_sendmsg_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 
 	if (unlikely(req->ctx->flags & IORING_SETUP_IOPOLL))
 		return -EINVAL;
+	if (unlikely(sqe->addr2 || sqe->file_index))
+		return -EINVAL;
 
 	sr->umsg = u64_to_user_ptr(READ_ONCE(sqe->addr));
 	sr->len = READ_ONCE(sqe->len);