My 2nd floor dryer vents outside of house but into the small enclosure between the roof and ceiling of the attached porch overhang (see photo below). There is no vent coming out of the overhang.
Yes, that's a problem!
Depending how long it's been set up like that, you may already need to replace the whole porch roof, and hope it hasn't rotted the wall framing too much.
Dryer exhaust needs to vent ALL THE WAY OUT of the BUILDING. "Air shall not be exhausted into an attic, soffit, ridge vent, or crawl space." (2015 IRC M1501.1)
Or you need a ventless (heat-pump) dryer that just needs a drain for the water. But you still may need a new porch roof.
If someone other than you installed it this way, you may have recourse to sue them for the cost of the new porch roof.
The whole point of a vent for a dryer is to take away the moisture contained in the air used to dry the wet/damp items in the dryer. That moist air will go to anywhere cooler than itself. So if it can't get straight out to atmosphere (fresh air), it will wander round inside the void - your roof space - until it finds somewhere suitable, on which to condense.
So, over time, the inside of that roof space will be damp every time you use the dryer. That will encourage rot and fungus there, increasing happily in secret. Until one day, you'll need to replace the timbers.
Solution: take the tube straight outside. If it goes through the roof space on its way, that's o.k., but its end must vent to outside. It will need some grille or flap to stop wildlife entering, and maybe will look a little ugly. Better than having to strip of at least part of the roof, though.
EDIT: With a little more info., like it's 12' to the side of that porch, I recommend taking the cladding off from above the front door, and putting a tube with an elbow between there and the dryer. Something like a sewer pipe may be an answer - not sure what diameter they are where you are. So now, the moist air (possibly gas if its a gas dryer) will travel from the back of the dryer, round 90 degrees, along the 12' to the left, with a bit of a slope, to a proper vent (flaps) out of the building above the door. Easy to take apart, easy to repair, and not unsightly. May help to take off a few tiles opposite the back of the dryer for easy access. Using non-flexi pipe means you'll be able to offer it through, and up to the hole where the dryer outlet is.