Input: uinput - zero-initialize uinput_ff_upload_compat to avoid info leak

Struct ff_effect_compat is embedded twice inside
uinput_ff_upload_compat, contains internal padding. In particular, there
is a hole after struct ff_replay to satisfy alignment requirements for
the following union member. Without clearing the structure,
copy_to_user() may leak stack data to userspace.

Initialize ff_up_compat to zero before filling valid fields.

Fixes: 2d56f3a ("Input: refactor evdev 32bit compat to be shareable with uinput")
Cc: stable@vger.kernel.org
Signed-off-by: Zhen Ni <zhen.ni@easystack.cn>
Link: https://lore.kernel.org/r/20250928063737.74590-1-zhen.ni@easystack.cn
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

Author: nizhen-t

drivers/input/misc/uinput.c

@@ -775,6 +775,7 @@ static int uinput_ff_upload_to_user(char __user *buffer,
 	if (in_compat_syscall()) {
 		struct uinput_ff_upload_compat ff_up_compat;
 
+		memset(&ff_up_compat, 0, sizeof(ff_up_compat));
 		ff_up_compat.request_id = ff_up->request_id;
 		ff_up_compat.retval = ff_up->retval;
 		/*