caddytls: fix permission requirement with AutomationPolicy (#6328)

Certificate automation has permission modules that are designed to
prevent inappropriate issuance of unbounded or wildcard certificates.
When an explicit cert manager is used, no additional permission should
be necessary. For example, this should be a valid caddyfile:

    https:// {
      tls {
        get_certificate tailscale
      }
      respond OK
    }

This is accomplished when provisioning an AutomationPolicy by tracking
whether there were explicit managers configured directly on the policy
(in the ManagersRaw field). Only when a number of potentially unsafe
conditions are present AND no explicit cert managers are configured is
an error returned.

The problem arises from the fact that ctx.LoadModule deletes the raw
bytes after loading in order to save memory. The first time an
AutomationPolicy is provisioned, the ManagersRaw field is populated, and
everything is fine.

An AutomationPolicy with no subjects is treated as a special "catch-all"
policy. App.createAutomationPolicies ensures that this catch-all policy
has an ACME issuer, and then calls its Provision method again because it
may have changed. This second time Provision is called, ManagesRaw is no
longer populated, and the permission check fails because it appears as
though the policy has no explicit managers.

Address this by storing a new boolean on AutomationPolicy recording
whether it had explicit cert managers configured on it.

Also fix an inverted boolean check on this value when setting
failClosed.

Updates #6060
Updates #6229
Updates #6327

Signed-off-by: Will Norris <will@tailscale.com>

1 files changed, 6 insertions, 3 deletions

diff --git a/modules/caddytls/automation.go b/modules/caddytls/automation.go
index 3f98125d..781818ed 100644
--- a/modules/caddytls/automation.go
+++ b/modules/caddytls/automation.go
@@ -170,6 +170,9 @@ type AutomationPolicy struct {
 	subjects []string
 	magic    *certmagic.Config
 	storage  certmagic.Storage
+
+	// Whether this policy had explicit managers configured directly on it.
+	hadExplicitManagers bool
 }
 
 // Provision sets up ap and builds its underlying CertMagic config.
@@ -201,8 +204,8 @@ func (ap *AutomationPolicy) Provision(tlsApp *TLS) error {
 	// store them on the policy before putting it on the config
 
 	// load and provision any cert manager modules
-	hadExplicitManagers := len(ap.ManagersRaw) > 0
 	if ap.ManagersRaw != nil {
+		ap.hadExplicitManagers = true
 		vals, err := tlsApp.ctx.LoadModule(ap, "ManagersRaw")
 		if err != nil {
 			return fmt.Errorf("loading external certificate manager modules: %v", err)
@@ -262,9 +265,9 @@ func (ap *AutomationPolicy) Provision(tlsApp *TLS) error {
 		// prevent issuance from Issuers (when Managers don't provide a certificate) if there's no
 		// permission module configured
 		noProtections := ap.isWildcardOrDefault() && !ap.onlyInternalIssuer() && (tlsApp.Automation == nil || tlsApp.Automation.OnDemand == nil || tlsApp.Automation.OnDemand.permission == nil)
-		failClosed := noProtections && hadExplicitManagers // don't allow on-demand issuance (other than implicit managers) if no managers have been explicitly configured
+		failClosed := noProtections && !ap.hadExplicitManagers // don't allow on-demand issuance (other than implicit managers) if no managers have been explicitly configured
 		if noProtections {
-			if !hadExplicitManagers {
+			if !ap.hadExplicitManagers {
 				// no managers, no explicitly-configured permission module, this is a config error
 				return fmt.Errorf("on-demand TLS cannot be enabled without a permission module to prevent abuse; please refer to documentation for details")
 			}