I inadvertently pierced the vent pipe from the toilet hanging up a picture! Now a year later I am noticing a faint bad smell in my bathroom. Could this be the culprit?

How do I fix the darn hole?
Thanks for any help

Possibly. Only solution is to open the wall and seal the hole. That said, I have drilled a small 1/4 hole through the drywall and then ran a Stainless Steel screw into the pipe to seal it and then patched the small wall hole. Could also
Be the wax ring under the toilet. Sniff around the toilet floor joint.

Brian has a good fix.

Cover screw or hole with silicone for added sealing.

Chuck