Came across this and find it very helpful with regard to legality.
In most countries of the world, Ayahuasca (containing DMT) has an undefined legal status.
The 1971 UN Convention on Psychotropic Drugs, an international treaty binding on all UN members, requires all UN member countries to schedule certain substances as illegal, including DMT.
However, the UN drug office has taken the official position that Ayahuasca is not covered by the proscription of DMT.
Thus, a country may choose to apply the laws against DMT to Ayahuasca, OR it may choose to exempt Ayahuasca, since the UN allows this exemption.
In most countries of the world, the choice has not been made yet -- and will not be made until a legal situation with Ayahuasca actually comes up.
The governments in countries where Ayahuasca has an undefined legal status can choose how they want to interpret the laws -- they can interpret them as saying Ayahuasca is legal or illegal.