There are a number of Eiríks sagas, but the answer is the same, regardless: The authorship of any of the sagas, whether Eiríks saga rauða, Eiríks saga viðförla, or Erex saga, is unknown. The earliest complete copy of any of them that we have is from the 14th century manuscripts Hauksbók, and then a 15th century manuscript called Skálholtsbók, but there is no attribution to the original 'author' of the sagas.

The idea of authorship in Scandinavian literature of that time is, at any rate, very different from the modern idea. Poets were praised for their ability to create verses that were complex and beautiful, and there is an entire list of them called Skáldatal, or "The List of Skálds", whereas it appears as though the creators of the sagas were left to toil in obscurity. Even exceptionally popular sagas, like Egils saga, don't have a defined authorship (it's theorized that Snorri Sturlusson had it written, but we can't be certain)