backport of commit 7ec3867 (#24031)

Co-authored-by: Nick Cabatoff <[email protected]>

Author: hc-github-team-secure-vault-core

changelog/24027.txt

@@ -0,0 +1,3 @@
+```release-note:bug
+expiration: Fix fatal error "concurrent map iteration and map write" when collecting metrics from leases.
+```

vault/expiration.go

@@ -884,7 +884,7 @@ func (m *ExpirationManager) Stop() error {
 	// for the next ExpirationManager to handle them.
 	newStrategy := ExpireLeaseStrategy(expireNoop)
 	m.expireFunc.Store(&newStrategy)
-	oldPending := m.pending
+	oldPending := &m.pending
 	m.pending, m.nonexpiring, m.irrevocable = sync.Map{}, sync.Map{}, sync.Map{}
 	m.leaseCount = 0
 	m.uniquePolicies = make(map[string][]string)
@@ -2490,7 +2490,7 @@ func (m *ExpirationManager) WalkTokens(walkFn ExpirationWalkFunction) error {
 	}
 
 	m.pendingLock.RLock()
-	toWalk := []sync.Map{m.pending, m.nonexpiring}
+	toWalk := []*sync.Map{&m.pending, &m.nonexpiring}
 	m.pendingLock.RUnlock()
 
 	for _, m := range toWalk {
@@ -2519,7 +2519,7 @@ func (m *ExpirationManager) walkLeases(walkFn leaseWalkFunction) error {
 	}
 
 	m.pendingLock.RLock()
-	toWalk := []sync.Map{m.pending, m.nonexpiring}
+	toWalk := []*sync.Map{&m.pending, &m.nonexpiring}
 	m.pendingLock.RUnlock()
 
 	for _, m := range toWalk {