From cff3c9b874bfdae38e6dc53de3a2fa1d2b8065af Mon Sep 17 00:00:00 2001
From: Tim Gross <tgross@hashicorp.com>
Date: Mon, 12 Jun 2023 08:53:56 -0400
Subject: [PATCH] replication: fix potential panic during upgrades (#17476)

If the authoritative region has been upgraded to a version of Nomad that has new
replicated objects (such as ACL Auth Methods, ACL Binding Rules, etc.), the
non-authoritative regions will start replicating those objects as soon as their
leader is upgraded. If a server in the non-authoritative region is upgraded and
then becomes the leader before all the other servers in the region have been
upgraded, then it will attempt to write a Raft log entry that the followers
don't understand. The followers will then panic.

Add same the minimum version checks that we do for RPC writes to the leader's
replication loop.
---
 .changelog/17476.txt |  3 +++
 nomad/leader.go      | 37 +++++++++++++++++++++++++++++++++++--
 2 files changed, 38 insertions(+), 2 deletions(-)
 create mode 100644 .changelog/17476.txt

diff --git a/.changelog/17476.txt b/.changelog/17476.txt
new file mode 100644
index 000000000000..f0de4c832ce5
--- /dev/null
+++ b/.changelog/17476.txt
@@ -0,0 +1,3 @@
+```release-note:bug
+replication: Fix a potential panic when a non-authoritative region is upgraded and a server with the new version becomes the leader.
+```
diff --git a/nomad/leader.go b/nomad/leader.go
index e6c7b760201a..ff07d5c77b66 100644
--- a/nomad/leader.go
+++ b/nomad/leader.go
@@ -58,7 +58,7 @@ var minACLRoleVersion = version.Must(version.NewVersion("1.4.0"))
 // minACLAuthMethodVersion is the Nomad version at which the ACL auth methods
 // table was introduced. It forms the minimum version all federated servers must
 // meet before the feature can be used.
-var minACLAuthMethodVersion = version.Must(version.NewVersion("1.5.0-beta.1"))
+var minACLAuthMethodVersion = version.Must(version.NewVersion("1.5.0"))
 
 // minACLJWTAuthMethodVersion is the Nomad version at which the ACL JWT auth method type
 // was introduced. It forms the minimum version all federated servers must
@@ -68,7 +68,7 @@ var minACLJWTAuthMethodVersion = version.Must(version.NewVersion("1.5.4"))
 // minACLBindingRuleVersion is the Nomad version at which the ACL binding rules
 // table was introduced. It forms the minimum version all federated servers
 // must meet before the feature can be used.
-var minACLBindingRuleVersion = version.Must(version.NewVersion("1.5.0-beta.1"))
+var minACLBindingRuleVersion = version.Must(version.NewVersion("1.5.0"))
 
 // minNomadServiceRegistrationVersion is the Nomad version at which the service
 // registrations table was introduced. It forms the minimum version all local
@@ -1848,6 +1848,17 @@ func (s *Server) replicateACLRoles(stopCh chan struct{}) {
 			// parameters are controlled internally.
 			_ = limiter.Wait(context.Background())
 
+			if !ServersMeetMinimumVersion(
+				s.serf.Members(), s.Region(), minACLRoleVersion, true) {
+				s.logger.Trace(
+					"all servers must be upgraded to 1.4.0 or later before ACL Roles can be replicated")
+				if s.replicationBackoffContinue(stopCh) {
+					continue
+				} else {
+					return
+				}
+			}
+
 			// Set the replication token on each replication iteration so that
 			// it is always current and can handle agent SIGHUP reloads.
 			req.AuthToken = s.ReplicationToken()
@@ -2046,6 +2057,17 @@ func (s *Server) replicateACLAuthMethods(stopCh chan struct{}) {
 			// parameters are controlled internally.
 			_ = limiter.Wait(context.Background())
 
+			if !ServersMeetMinimumVersion(
+				s.serf.Members(), s.Region(), minACLAuthMethodVersion, true) {
+				s.logger.Trace(
+					"all servers must be upgraded to 1.5.0 or later before ACL Auth Methods can be replicated")
+				if s.replicationBackoffContinue(stopCh) {
+					continue
+				} else {
+					return
+				}
+			}
+
 			// Set the replication token on each replication iteration so that
 			// it is always current and can handle agent SIGHUP reloads.
 			req.AuthToken = s.ReplicationToken()
@@ -2241,6 +2263,17 @@ func (s *Server) replicateACLBindingRules(stopCh chan struct{}) {
 			// parameters are controlled internally.
 			_ = limiter.Wait(context.Background())
 
+			if !ServersMeetMinimumVersion(
+				s.serf.Members(), s.Region(), minACLBindingRuleVersion, true) {
+				s.logger.Trace(
+					"all servers must be upgraded to 1.5.0 or later before ACL Binding Rules can be replicated")
+				if s.replicationBackoffContinue(stopCh) {
+					continue
+				} else {
+					return
+				}
+			}
+
 			// Set the replication token on each replication iteration so that
 			// it is always current and can handle agent SIGHUP reloads.
 			req.AuthToken = s.ReplicationToken()