The RPC handlers expect to see `nil` ACL objects whenever ACLs are disabled. By
using `nil` as a sentinel value, we have the risk of nil pointer exceptions and
improper handling of `nil` when returned from our various auth methods that can
lead to privilege escalation bugs. This is the final patch in a series to
eliminate the use of `nil` ACLs as a sentinel value for when ACLs are disabled.
This patch adds a new virtual ACL policy field for when ACLs are disabled and
updates our authentication logic to use it. Included:
* Extends auth package tests to demonstrate that nil ACLs are treated as failed
auth and disabled ACLs succeed auth.
* Adds a new `AllowDebug` ACL check for the weird special casing we have for
pprof debugging when ACLs are disabled.
* Removes the remaining unexported methods (and repeated tests) from the
`nomad/acl.go` file.
* Update the semgrep rules to detect improper nil ACL checking and remove the
old invalid ACL checks.
* Update the contributing guide for RPC authentication.
Ref: https://github.com/hashicorp/nomad-enterprise/pull/1218
Ref: https://github.com/hashicorp/nomad/pull/18703
Ref: https://github.com/hashicorp/nomad/pull/18715
Ref: https://github.com/hashicorp/nomad/pull/16799
Ref: https://github.com/hashicorp/nomad/pull/18730
Ref: https://github.com/hashicorp/nomad/pull/18744
Fixes#16517
Given a 3 Server cluster with at least 1 Client connected to Follower 1:
If a NodeMeta.{Apply,Read} for the Client request is received by
Follower 1 with `AllowStale = false` the Follower will forward the
request to the Leader.
The Leader, not being connected to the target Client, will forward the
RPC to Follower 1.
Follower 1, seeing AllowStale=false, will forward the request to the
Leader.
The Leader, not being connected to... well hoppefully you get the
picture: an infinite loop occurs.
