You can access master page controls. You always have access to Master page from its content page through "this.Master"
You can expose various needs through properties of Master Page.
If you need to access the control then you can use:
this.Master.FindControl()
Once you get the control, cast it into valid type and have an access to all the valid properties of that control.
Google gave this as first link for more reference if needed:
Accessing Master Page Members from Content Pages in ASP.Net [
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