Charis SIL is based on Bitstream Charter, one of the first fonts designed for laser printers. The resemblance is so close that Charis SIL includes Charter's license in the copyright notice.

Umm… is this legit?

It seems to be.
This accompanies the Bitstream Charter fonts:

(c) Copyright 1989-1992, Bitstream Inc., Cambridge, MA.

You are hereby granted permission under all Bitstream propriety rights to use, copy, modify, sublicense, sell, and redistribute the 4 Bitstream Charter (r) Type 1 outline fonts and the 4 Courier Type 1 outline fonts for any purpose and without restriction; provided, that this notice is left intact on all copies of such fonts and that Bitstream's trademark is acknowledged as shown below on all unmodified copies of the 4 Charter Type 1 fonts.

BITSTREAM CHARTER is a registered trademark of Bitstream Inc.

People at SIL have added a lot of characters needed by many minority languages. These fonts allow missionaries under the auspice of organisation affiliated with SIL to translate and publish in the those languages, but most importantly it gives the people themselves better access to orthographies of their languages.

Adobe donated the basic styles of Utopia, Bitstream donated the basic styles of Charter and Courier, and URW donated the basic styles of Nimbus Sans, Nimbus Roman and Courier to various open-source projects under pretty flexible terms. Quite a few derivative designs have legitimately emerged from these donations.

I should note though that if you want a serious Cyrillic Charter, you should get the one designed by Vladimir Yefimov and published by ParaType rather than the one that comes with Charis, which is rather hideous.

A.