STM32 Output current capabilities

The rules are simple.

If between Vss and Vdd you can to 25mA on one pin.
All pins together may do 80 mA. So 80mA in and 80mA out.
All currents should stay within 120mA, either way.

The current the chip itself uses subtracts from both ΣIvdd and ΣIvss.

Example: it is possible to sink 50ma and source 50mA with only 4 pins. (don't do that though)

If outside Vss to Vdd, 5mA max, polarity doesn't matter.

However, there is a caveat! Look at the Output voltage characteristics.
You may be looking at a 400 mV drop in voltage over the pin.

And every milliamp of current through the chip adds to the package power, see the chapter about thermals.

Your current source is going to source 9 mA. The microcontroller is going to sink it.

The maximum current for any one pin is 25 mA sink or source so your maximum of 9 mA is very safe. Watch out for the chip total current if you have multiple current sources that can be on simultaneously.