As noted, there is something done automatically. But: there is also a form that you need to sign off before/at the ceremony (it's in the instructions) that you've not been charged with (etc etc) a serious crime, committed genocide, you know, the usual.
You're to inform the officers if you can't sign the form (that you have been charged or whatever). I believe in most cases this means they'd delay the ceremony for that person (if you can't sign the form) so that they can look into it/clarify whether it's something that would prohibit one from becoming a citizen.
The sense of this is that if you're later found to have lied about this, you've committed misrepresentation, one of the (very few) ways that can make your citizenship revocable.
Obviously this doesn't happen a lot, but there are cases - there was a woman, last year or the year before, who was charged by the Russian govt with some (obviously political) crimes and they had to clarify whether it was also a crime under Canadian law. Obviously it should not have been but some junior officer didn't understand the context and started comparing it to Canadian criminal code and it became a mini-scandal until someone with a brain intervened (and she got the oath ceremony quickly after this idiocy became public).
