I'm running Ubuntu 20.04. I installed Rocksmith using Steam and have been playing that for a few months. I bought Cherub Rock and installed the DLL to be able to play CDLC. CDLC is working. I did notice that when I play a song, Mastery shows 100% (typically when playing Rhythm guitar - when playing Lead, Mastery appears correct). Does CFSM correct this? And if so, is anyone here running it under Ubuntu on Wine? Any installation hints to get it installed in Wine and able to see my CDLC? 

CFSM's song repair options (or more precisely adding Dynamic Difficulty) will indeed repair 100% mastery bug.

It can be run on Mac using Wine, so I'd say it should be possible to get it to run on Ubuntu as well, but I can't really help you with this since I haven't ever tried to get it to run.

Just an update in case other folks are trying the same. I have PlayOnLinux installed. That made it pretty simple to install CFSM in a new virtual drive. However, CFSM could not find my Rocksmith2014 directory, since that was installed in a different virtual drive in a hidden directory using Steam's installer. I made a symlink to my Rocksmith2014 directory, and CFSM was able to start up and see my CDLC directory. it does do the Dynamic Difficulty repairs and the 100% Mastery bug repair. CFSM really helps out when using older CDLC. 

(I'm not sure how to get all the parts working together to actually make CDLC. I'm thinking next PC will be Windows just to simplify getting set up, although I might hack around a bit. I'm kinda liking The Cramps and don't see any CDLC for them.)