Linux 5.13 was the first kernel release with Landlock incorporated, but the Landlock project is from 2016 also.
I found the announcement email for Landlock posted to the lkml[1] where the author compares the project to Pledge. There's also his talk[2] from 2016 if you're interested. I was certain landlock predated pledge, as I thought the website or earliest talk was from late 2015, but I am less certain now, indeed I seem to have been wrong in my claim.
As for either being the first, at the very least Seatbelt from Apple has a paper dated 2011[3] and was released with macOS 10.5.
OpenBSD's pledge(2) was first talked about publicly as tame(2), and was presented in at FSec 2015, it was renamed pledge(2) as mentioned on the OpenBSD 5.9 page.
I thought I had remembered something from Landlock from 2015 also, but can't find anything supporting that. The first version referenced is v7 or v0.7, so it's possible there was a talk for v0.1 or something that isn't online anywhere.
I'll concede that's less likely and I'm probably just wrong and misremembering though.
I found the announcement email for Landlock posted to the lkml[1] where the author compares the project to Pledge. There's also his talk[2] from 2016 if you're interested. I was certain landlock predated pledge, as I thought the website or earliest talk was from late 2015, but I am less certain now, indeed I seem to have been wrong in my claim.
As for either being the first, at the very least Seatbelt from Apple has a paper dated 2011[3] and was released with macOS 10.5.
[1] https://lwn.net/Articles/700607/
[2] https://archives.kernel-recipes.org/document/landlock-lsm-un...
[3] https://www.ise.io/wp-content/uploads/2017/07/apple-sandbox....