config: Protect file_mem_backend against annotation attacks

This one could theoretically be used to overwrite data on the host.
It seems somewhat less risky than the earlier ones for a number
of reasons, but worth protecting a little anyway.

Fixes: #901

Signed-off-by: Christophe de Dinechin <dinechin@redhat.com>

src/runtime/virtcontainers/hypervisor.go

@@ -330,6 +330,9 @@ type HypervisorConfig struct {
 	// File based memory backend root directory
 	FileBackedMemRootDir string
 
+	// FileBackedMemRootList is the list of valid root directories values for annotations
+	FileBackedMemRootList []string
+
 	// customAssets is a map of assets.
 	// Each value in that map takes precedence over the configured assets.
 	// For example, if there is a value for the "kernel" key in this map,

src/runtime/virtcontainers/persist.go

@@ -236,6 +236,7 @@ func (s *Sandbox) dumpConfig(ss *persistapi.SandboxState) {
 		MemPrealloc:             sconfig.HypervisorConfig.MemPrealloc,
 		HugePages:               sconfig.HypervisorConfig.HugePages,
 		FileBackedMemRootDir:    sconfig.HypervisorConfig.FileBackedMemRootDir,
+		FileBackedMemRootList:   sconfig.HypervisorConfig.FileBackedMemRootList,
 		Realtime:                sconfig.HypervisorConfig.Realtime,
 		Mlock:                   sconfig.HypervisorConfig.Mlock,
 		DisableNestingChecks:    sconfig.HypervisorConfig.DisableNestingChecks,
@@ -503,6 +504,7 @@ func loadSandboxConfig(id string) (*SandboxConfig, error) {
 		MemPrealloc:             hconf.MemPrealloc,
 		HugePages:               hconf.HugePages,
 		FileBackedMemRootDir:    hconf.FileBackedMemRootDir,
+		FileBackedMemRootList:   hconf.FileBackedMemRootList,
 		Realtime:                hconf.Realtime,
 		Mlock:                   hconf.Mlock,
 		DisableNestingChecks:    hconf.DisableNestingChecks,

src/runtime/virtcontainers/persist/api/config.go

@@ -116,6 +116,9 @@ type HypervisorConfig struct {
 	// File based memory backend root directory
 	FileBackedMemRootDir string
 
+	// FileBackedMemRootList is the list of valid root directories values for annotations
+	FileBackedMemRootList []string
+
 	// BlockDeviceCacheSet specifies cache-related options will be set to block devices or not.
 	BlockDeviceCacheSet bool
 

src/runtime/virtcontainers/pkg/oci/utils.go

@@ -375,7 +375,7 @@ func addHypervisorConfigOverrides(ocispec specs.Spec, config *vc.SandboxConfig,
 		return err
 	}
 
-	if err := addHypervisorMemoryOverrides(ocispec, config); err != nil {
+	if err := addHypervisorMemoryOverrides(ocispec, config, runtime); err != nil {
 		return err
 	}
 
@@ -497,7 +497,7 @@ func addHypervisorConfigOverrides(ocispec specs.Spec, config *vc.SandboxConfig,
 	return nil
 }
 
-func addHypervisorMemoryOverrides(ocispec specs.Spec, sbConfig *vc.SandboxConfig) error {
+func addHypervisorMemoryOverrides(ocispec specs.Spec, sbConfig *vc.SandboxConfig, runtime RuntimeConfig) error {
 	if value, ok := ocispec.Annotations[vcAnnotations.DefaultMemory]; ok {
 		memorySz, err := strconv.ParseUint(value, 10, 32)
 		if err != nil {
@@ -561,6 +561,9 @@ func addHypervisorMemoryOverrides(ocispec specs.Spec, sbConfig *vc.SandboxConfig
 	}
 
 	if value, ok := ocispec.Annotations[vcAnnotations.FileBackedMemRootDir]; ok {
+		if !regexpContains(runtime.HypervisorConfig.FileBackedMemRootList, value) {
+			return fmt.Errorf("file_mem_backend value %v required from annotation is not valid", value)
+		}
 		sbConfig.HypervisorConfig.FileBackedMemRootDir = value
 	}