Diagnosis
The adjustable bar oil pump is set too high, or oiler plunger (if you have that model) is stuck partially engaged.
How to Fix It
On the MS 170, there's a small screw on the bottom of the saw, near the clutch cover, that controls the oil pump output. Turning it clockwise (toward the minus sign) reduces oil flow. Start with a quarter-turn reduction, run the saw, and check. You want a light line of oil flung off the chain, not a spray.
If That Didn't Work
The oil pump itself might be worn or damaged, allowing too much oil past its metering groove. That requires pump replacement.
Heads Up
Using thin, non-Stihl bar oil in cold weather can also cause excessive flow because it's less viscous. Always use the proper oil for the temperature.