client template configuration for file sandboxing

client/allocrunner/taskrunner/template/template.go

@@ -573,12 +573,9 @@ func parseTemplateConfigs(config *TaskTemplateManagerConfig) (map[*ctconf.Templa
 		ct.Contents = &tmpl.EmbeddedTmpl
 		ct.LeftDelim = &tmpl.LeftDelim
 		ct.RightDelim = &tmpl.RightDelim
-
-		// By default we pass a blacklist of functions to prevent
-		// task operators from bypassing client-task isolation.
-		// This protection can be disabled by the client config.
-		if !config.ClientConfig.EnableInsecureTemplateFunctions {
-			ct.FunctionBlacklist = []string{"plugin", "file"}
+		ct.FunctionBlacklist = config.ClientConfig.TemplateConfig.FunctionBlacklist
+		if !config.ClientConfig.TemplateConfig.DisableSandbox {
+			ct.SandboxPath = &config.TaskDir
 		}
 
 		// Set the permissions

client/config/config.go

@@ -201,9 +201,8 @@ type Config struct {
 	// DisableRemoteExec disables remote exec targeting tasks on this client
 	DisableRemoteExec bool
 
-	// EnableInsecureTemplateFunctions enables templates to include functions
-	// that are unsafe because they expose information from the client host.
-	EnableInsecureTemplateFunctions bool
+	// TemplateConfig includes configuration for template rendering
+	TemplateConfig *ClientTemplateConfig
 
 	// BackwardsCompatibleMetrics determines whether to show methods of
 	// displaying metrics for older versions, or to only show the new format
@@ -252,6 +251,11 @@ type Config struct {
 	AutoFetchCNIDir string
 }
 
+type ClientTemplateConfig struct {
+	FunctionBlacklist []string
+	DisableSandbox    bool
+}
+
 func (c *Config) Copy() *Config {
 	nc := new(Config)
 	*nc = *c
@@ -266,26 +270,29 @@ func (c *Config) Copy() *Config {
 // DefaultConfig returns the default configuration
 func DefaultConfig() *Config {
 	return &Config{
-		Version:                         version.GetVersion(),
-		VaultConfig:                     config.DefaultVaultConfig(),
-		ConsulConfig:                    config.DefaultConsulConfig(),
-		LogOutput:                       os.Stderr,
-		Region:                          "global",
-		StatsCollectionInterval:         1 * time.Second,
-		TLSConfig:                       &config.TLSConfig{},
-		LogLevel:                        "DEBUG",
-		GCInterval:                      1 * time.Minute,
-		GCParallelDestroys:              2,
-		GCDiskUsageThreshold:            80,
-		GCInodeUsageThreshold:           70,
-		GCMaxAllocs:                     50,
-		NoHostUUID:                      true,
-		DisableTaggedMetrics:            false,
-		DisableRemoteExec:               false,
-		EnableInsecureTemplateFunctions: false,
-		BackwardsCompatibleMetrics:      false,
-		RPCHoldTimeout:                  5 * time.Second,
-		AutoFetchCNI:                    false,
+		Version:                 version.GetVersion(),
+		VaultConfig:             config.DefaultVaultConfig(),
+		ConsulConfig:            config.DefaultConsulConfig(),
+		LogOutput:               os.Stderr,
+		Region:                  "global",
+		StatsCollectionInterval: 1 * time.Second,
+		TLSConfig:               &config.TLSConfig{},
+		LogLevel:                "DEBUG",
+		GCInterval:              1 * time.Minute,
+		GCParallelDestroys:      2,
+		GCDiskUsageThreshold:    80,
+		GCInodeUsageThreshold:   70,
+		GCMaxAllocs:             50,
+		NoHostUUID:              true,
+		DisableTaggedMetrics:    false,
+		DisableRemoteExec:       false,
+		TemplateConfig: &ClientTemplateConfig{
+			FunctionBlacklist: []string{"plugin"},
+			DisableSandbox:    false,
+		},
+		BackwardsCompatibleMetrics: false,
+		RPCHoldTimeout:             5 * time.Second,
+		AutoFetchCNI:               false,
 	}
 }
 

command/agent/agent.go

@@ -469,7 +469,8 @@ func convertClientConfig(agentConfig *Config) (*clientconfig.Config, error) {
 	conf.ClientMaxPort = uint(agentConfig.Client.ClientMaxPort)
 	conf.ClientMinPort = uint(agentConfig.Client.ClientMinPort)
 	conf.DisableRemoteExec = agentConfig.Client.DisableRemoteExec
-	conf.EnableInsecureTemplateFunctions = agentConfig.Client.EnableInsecureTemplateFunctions
+	conf.TemplateConfig.FunctionBlacklist = agentConfig.Client.TemplateConfig.FunctionBlacklist
+	conf.TemplateConfig.DisableSandbox = agentConfig.Client.TemplateConfig.DisableSandbox
 
 	// Setup the node
 	conf.Node = new(structs.Node)

command/agent/config.go

@@ -242,9 +242,8 @@ type ClientConfig struct {
 	// DisableRemoteExec disables remote exec targeting tasks on this client
 	DisableRemoteExec bool `hcl:"disable_remote_exec"`
 
-	// EnableInsecureTemplateFunctions enables templates to include functions
-	// that are unsafe because they expose information from the client host.
-	EnableInsecureTemplateFunctions bool `hcl:"enable_insecure_template_functions"`
+	// TemplateConfig includes configuration for template rendering
+	TemplateConfig *ClientTemplateConfig `hcl:"template"`
 
 	// ServerJoin contains information that is used to attempt to join servers
 	ServerJoin *ServerJoin `hcl:"server_join"`
@@ -276,6 +275,20 @@ type ClientConfig struct {
 	AutoFetchCNIPluginsURL string `hcl:"auto_fetch_cni_plugins_url"`
 }
 
+// ClientTemplateConfig is configuration on the client specific to template
+// rendering
+type ClientTemplateConfig struct {
+
+	// FunctionBlacklist disables functions in consul-template that
+	// are unsafe because they expose information from the client host.
+	FunctionBlacklist []string `hcl:"function_blacklist"`
+
+	// DisableSandbox allows templates to access arbitrary files on the
+	// client host. By default templates can access files only within
+	// the task directory.
+	DisableSandbox bool `hcl:"disable_sandbox"`
+}
+
 // ACLConfig is configuration specific to the ACL system
 type ACLConfig struct {
 	// Enabled controls if we are enforce and manage ACLs
@@ -685,7 +698,10 @@ func DevConfig() *Config {
 	conf.Client.GCDiskUsageThreshold = 99
 	conf.Client.GCInodeUsageThreshold = 99
 	conf.Client.GCMaxAllocs = 50
-	conf.Client.EnableInsecureTemplateFunctions = false
+	conf.Client.TemplateConfig = &ClientTemplateConfig{
+		FunctionBlacklist: []string{"plugin"},
+		DisableSandbox:    false,
+	}
 	conf.Telemetry.PrometheusMetrics = true
 	conf.Telemetry.PublishAllocationMetrics = true
 	conf.Telemetry.PublishNodeMetrics = true
@@ -728,6 +744,10 @@ func DefaultConfig() *Config {
 				RetryInterval:    30 * time.Second,
 				RetryMaxAttempts: 0,
 			},
+			TemplateConfig: &ClientTemplateConfig{
+				FunctionBlacklist: []string{"plugin"},
+				DisableSandbox:    false,
+			},
 		},
 		Server: &ServerConfig{
 			Enabled:   false,
@@ -1307,8 +1327,8 @@ func (a *ClientConfig) Merge(b *ClientConfig) *ClientConfig {
 		result.DisableRemoteExec = b.DisableRemoteExec
 	}
 
-	if b.EnableInsecureTemplateFunctions {
-		result.EnableInsecureTemplateFunctions = true
+	if b.TemplateConfig != nil {
+		result.TemplateConfig = b.TemplateConfig
 	}
 
 	// Add the servers

command/agent/config_test.go

@@ -88,13 +88,16 @@ func TestConfig_Merge(t *testing.T) {
 			Options: map[string]string{
 				"foo": "bar",
 			},
-			NetworkSpeed:                    100,
-			CpuCompute:                      100,
-			MemoryMB:                        100,
-			MaxKillTimeout:                  "20s",
-			ClientMaxPort:                   19996,
-			DisableRemoteExec:               false,
-			EnableInsecureTemplateFunctions: true,
+			NetworkSpeed:      100,
+			CpuCompute:        100,
+			MemoryMB:          100,
+			MaxKillTimeout:    "20s",
+			ClientMaxPort:     19996,
+			DisableRemoteExec: false,
+			TemplateConfig: &ClientTemplateConfig{
+				FunctionBlacklist: []string{"plugin"},
+				DisableSandbox:    false,
+			},
 			Reserved: &Resources{
 				CPU:           10,
 				MemoryMB:      10,
@@ -246,15 +249,18 @@ func TestConfig_Merge(t *testing.T) {
 				"foo": "bar",
 				"baz": "zip",
 			},
-			ChrootEnv:                       map[string]string{},
-			ClientMaxPort:                   20000,
-			ClientMinPort:                   22000,
-			NetworkSpeed:                    105,
-			CpuCompute:                      105,
-			MemoryMB:                        105,
-			MaxKillTimeout:                  "50s",
-			DisableRemoteExec:               false,
-			EnableInsecureTemplateFunctions: true,
+			ChrootEnv:         map[string]string{},
+			ClientMaxPort:     20000,
+			ClientMinPort:     22000,
+			NetworkSpeed:      105,
+			CpuCompute:        105,
+			MemoryMB:          105,
+			MaxKillTimeout:    "50s",
+			DisableRemoteExec: false,
+			TemplateConfig: &ClientTemplateConfig{
+				FunctionBlacklist: []string{"plugin"},
+				DisableSandbox:    false,
+			},
 			Reserved: &Resources{
 				CPU:           15,
 				MemoryMB:      15,

website/source/docs/configuration/client.html.md

@@ -58,9 +58,9 @@ driver) but will be removed in a future release.
 - `disable_remote_exec` `(bool: false)` - Specifies if the client should disable
   remote task execution to tasks running on this client.
 
-- `enable_insecure_template_functions` `(bool: false)` - Specifies if the client
-  should enable template rendering functions that can leak information from the
-  client host to templates.
+- `template_function_blacklist` `([]string: ["plugin", "file"])` - Specifies a
+  list of template rendering functions that should be disallowed in job specs
+  because they can leak information from the client host to templates.
 
 - `meta` `(map[string]string: nil)` - Specifies a key-value map that annotates
   with user-defined metadata.