io_uring: check for valid register opcode earlier

We only check the register opcode value inside the restricted ring
section, move it into the main io_uring_register() function instead
and check it up front.
Signed-off-by: Jens Axboe <axboe@kernel.dk>

io_uring/io_uring.c

@@ -4020,8 +4020,6 @@ static int __io_uring_register(struct io_ring_ctx *ctx, unsigned opcode,
 		return -EEXIST;
 
 	if (ctx->restricted) {
-		if (opcode >= IORING_REGISTER_LAST)
-			return -EINVAL;
 		opcode = array_index_nospec(opcode, IORING_REGISTER_LAST);
 		if (!test_bit(opcode, ctx->restrictions.register_op))
 			return -EACCES;
@@ -4177,6 +4175,9 @@ SYSCALL_DEFINE4(io_uring_register, unsigned int, fd, unsigned int, opcode,
 	long ret = -EBADF;
 	struct fd f;
 
+	if (opcode >= IORING_REGISTER_LAST)
+		return -EINVAL;
+
 	f = fdget(fd);
 	if (!f.file)
 		return -EBADF;