io_uring: verify pad field is 0 in io_get_ext_arg

Ensure that only 0 is passed for pad here.

Fixes: c73ebb68 ("io_uring: add timeout support for io_uring_enter()")
Signed-off-by: Dylan Yudaken <dylany@fb.com>
Link: https://lore.kernel.org/r/20220412163042.2788062-5-dylany@fb.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

fs/io_uring.c

@@ -10711,6 +10711,8 @@ static int io_get_ext_arg(unsigned flags, const void __user *argp, size_t *argsz
 		return -EINVAL;
 	if (copy_from_user(&arg, argp, sizeof(arg)))
 		return -EFAULT;
+	if (arg.pad)
+		return -EINVAL;
 	*sig = u64_to_user_ptr(arg.sigmask);
 	*argsz = arg.sigmask_sz;
 	*ts = u64_to_user_ptr(arg.ts);