projectquota: protect concurrent map access

Protect access to q.quotas map, and lock around changing nextProjectID.

Techinically, the lock in findNextProjectID() is not needed as it is
only called during initialization, but one can never be too careful.

Fixes: 52897d1c092 ("projectquota: utility class for project quota controls")
Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

daemon/graphdriver/quota/projectquota.go

@@ -153,9 +153,11 @@ func NewControl(basePath string) (*Control, error) {
 // SetQuota - assign a unique project id to directory and set the quota limits
 // for that project id
 func (q *Control) SetQuota(targetPath string, quota Quota) error {
-
+	q.RLock()
 	projectID, ok := q.quotas[targetPath]
+	q.RUnlock()
 	if !ok {
+		q.Lock()
 		projectID = q.nextProjectID
 
 		//
@@ -163,11 +165,12 @@ func (q *Control) SetQuota(targetPath string, quota Quota) error {
 		//
 		err := setProjectID(targetPath, projectID)
 		if err != nil {
+			q.Unlock()
 			return err
 		}
-
 		q.quotas[targetPath] = projectID
 		q.nextProjectID++
+		q.Unlock()
 	}
 
 	//
@@ -204,8 +207,9 @@ func setProjectQuota(backingFsBlockDev string, projectID uint32, quota Quota) er
 
 // GetQuota - get the quota limits of a directory that was configured with SetQuota
 func (q *Control) GetQuota(targetPath string, quota *Quota) error {
-
+	q.RLock()
 	projectID, ok := q.quotas[targetPath]
+	q.RUnlock()
 	if !ok {
 		return errors.Errorf("quota not found for path: %s", targetPath)
 	}
@@ -276,6 +280,8 @@ func setProjectID(targetPath string, projectID uint32) error {
 // findNextProjectID - find the next project id to be used for containers
 // by scanning driver home directory to find used project ids
 func (q *Control) findNextProjectID(home string) error {
+	q.Lock()
+	defer q.Unlock()
 	files, err := ioutil.ReadDir(home)
 	if err != nil {
 		return errors.Errorf("read directory failed: %s", home)

daemon/graphdriver/quota/types.go

@@ -2,6 +2,8 @@
 
 package quota // import "github.com/docker/docker/daemon/graphdriver/quota"
 
+import "sync"
+
 // Quota limit params - currently we only control blocks hard limit
 type Quota struct {
 	Size uint64
@@ -11,6 +13,7 @@ type Quota struct {
 // who wants to apply project quotas to container dirs
 type Control struct {
 	backingFsBlockDev string
+	sync.RWMutex      // protect nextProjectID and quotas map
 	nextProjectID     uint32
 	quotas            map[string]uint32
 }