tracing: Prevent bad count for tracing_cpumask_write

commit 98feccbf upstream.

If a large count is provided, it will trigger a warning in bitmap_parse_user.
Also check zero for it.

Cc: stable@vger.kernel.org
Fixes: 9e01c1b7 ("cpumask: convert kernel trace functions")
Link: https://lore.kernel.org/20241216073238.2573704-1-lizhi.xu@windriver.com


Reported-by:  <syzbot+0aecfd34fb878546f3fd@syzkaller.appspotmail.com>
Closes: https://syzkaller.appspot.com/bug?extid=0aecfd34fb878546f3fd


Tested-by:  <syzbot+0aecfd34fb878546f3fd@syzkaller.appspotmail.com>
Signed-off-by: Lizhi Xu <lizhi.xu@windriver.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>