Not remotely likely Leadbelly wrote it "from scratch," though he standardized and popularized it. I suspect at least some of his songs were picked up while he was chauffeuring John Lomax on various field trips after he got out of Angola.

"Rock Island Line," e.g., was (according to Wolfe & Lornell's bio) learned at an Arkansas prison while he was on a trip with Lomax, though Leadbelly "quickly appropriated" it. He made it his own, of course.

The first recording of "Linin' Track" that I can see is a 1940 cut, with the Golden Gate Quartet, in Huddie's Victor session. I don't recall where/when the version led by Henry Truvillion was recorded but I wouldn't be a bit surprised if that's where Leadbelly learned the song. Despite the # of work songs in his later repertoire, he recorded none at all (except "Julie Ann Johnson") in his earlier sessions but did a few in a marathon 1935 session for Lomax in Connecticut, at the same time he was also recording for ARC in a stab at the commercial market, and added more as he became a fixture in the NY folk scene. That could just reflect the approach Lomax took to Leadbelly's repertoire at their earliest meetings, of course.

Bruce Jackson's Wake Up, Dead Man shows the persistence of these songs in the Texas prison tradition, well into the 1960s, but from the evidence of his discography, it's not clear how many Huddie learned personally while he was in jail vs how many he may have picked up from the Lomax' collection of field recordings. Naturally the copyright boys prefer a "Words & Music by" as opposed to an "Arranged & Adapted by" credit.