You can use
ACL and the command
setfacl for that.
ACL entries consist of a user (u), group (g), other (o) and an effective rights mask (m). An effective rights mask defines the most restrictive level of permissions.
setfacl sets the permissions for a given file or directory.
getfacl shows the permissions for a given file or directory.
Defaults for a given object can be defined.
ACLs can be applied to users or groups but it is easier to manage groups. Groups scale better than continuously adding or subtracting users.
This is the part you are after:
Copying an ACL into the Default ACL
Once the ACLs are the way they need to be, they can be set as the default. Defaults are inherited, so a new directory will inherit the defaults of the parent directory.
getfacl -a /path/to/dir | setfacl -d -M- /path/to/dir
You do need to add the
acl option when mounting. In
acl to the options for your disc. Make sure to use a LABEL and not a UUID.
LABEL="ExternalUsbDisc" /media/usb-disc ext4 defaults,acl 0 2