The Bulls were required to sign a 13th player to their roster, and did so in acquiring Jarvis Varnado on a 10-day contract. Varnado has been in the DLeague with the Iowa Energy for this season, a shotblocker who our own Ridiculous Upside recently pegged as their #3 Center prospect.
Varnado is 25 and has spent much of his NBA existence with Miami.
This roster move is the likely start of what Mark Deeks called "an intricate and embarrassing balancing act" where the Bulls sign players for 10 days, then wait 2 weeks on a 12-man roster, then repeat. All to avoid this year's luxury tax which is still a present danger given possible (some known, some not) incentives due to Taj Gibson and Joakim Noah.
On that front, I'd only expect a trade of Dunleavy or Hinrich if they determine they need to get more breathing room.