This patch reworks the SELinux patch to be only run on demand by the daemon

Added --selinux-enable switch to daemon to enable SELinux labeling.

The daemon will now generate a new unique random SELinux label when a
container starts, and remove it when the container is removed.   The MCS
labels will be stored in the daemon memory.  The labels of containers will
be stored in the container.json file.

When the daemon restarts on boot or if done by an admin, it will read all containers json files and reserve the MCS labels.

A potential problem would be conflicts if you setup thousands of containers,
current scheme would handle ~500,000 containers.

Docker-DCO-1.1-Signed-off-by: Dan Walsh <dwalsh@redhat.com> (github: rhatdan)
Docker-DCO-1.1-Signed-off-by: Dan Walsh <dwalsh@redhat.com> (github: crosbymichael)

label/label.go

@@ -24,3 +24,7 @@ func GetPidCon(pid int) (string, error) {
 
 func Init() {
 }
+
+func ReserveLabel(label string) error {
+	return nil
+}

label/label_selinux.go

@@ -75,3 +75,7 @@ func GetPidCon(pid int) (string, error) {
 func Init() {
 	selinux.SelinuxEnabled()
 }
+
+func ReserveLabel(label string) {
+	selinux.ReserveLabel(label)
+}

selinux/selinux.go

@@ -204,6 +204,13 @@ func NewContext(scon string) SELinuxContext {
 	return c
 }
 
+func ReserveLabel(scon string) {
+	if len(scon) != 0 {
+		con := strings.SplitN(scon, ":", 4)
+		mcsAdd(con[3])
+	}
+}
+
 func SelinuxGetEnforce() int {
 	var enforce int
 
@@ -229,8 +236,12 @@ func SelinuxGetEnforceMode() int {
 	return Disabled
 }
 
-func mcsAdd(mcs string) {
+func mcsAdd(mcs string) error {
+	if mcsList[mcs] {
+		return fmt.Errorf("MCS Label already exists")
+	}
 	mcsList[mcs] = true
+	return nil
 }
 
 func mcsDelete(mcs string) {
@@ -283,15 +294,21 @@ func uniqMcs(catRange uint32) string {
 			}
 		}
 		mcs = fmt.Sprintf("s0:c%d,c%d", c1, c2)
-		if mcsExists(mcs) {
+		if err := mcsAdd(mcs); err != nil {
 			continue
 		}
-		mcsAdd(mcs)
 		break
 	}
 	return mcs
 }
 
+func FreeLxcContexts(scon string) {
+	if len(scon) != 0 {
+		con := strings.SplitN(scon, ":", 4)
+		mcsDelete(con[3])
+	}
+}
+
 func GetLxcContexts() (processLabel string, fileLabel string) {
 	var (
 		val, key string
@@ -344,7 +361,8 @@ func GetLxcContexts() (processLabel string, fileLabel string) {
 	}
 
 exit:
-	mcs := IntToMcs(os.Getpid(), 1024)
+	//	mcs := IntToMcs(os.Getpid(), 1024)
+	mcs := uniqMcs(1024)
 	scon := NewContext(processLabel)
 	scon["level"] = mcs
 	processLabel = scon.Get()
@@ -373,6 +391,8 @@ func CopyLevel(src, dest string) (string, error) {
 	}
 	scon := NewContext(src)
 	tcon := NewContext(dest)
+	mcsDelete(tcon["level"])
+	mcsAdd(scon["level"])
 	tcon["level"] = scon["level"]
 	return tcon.Get(), nil
 }

selinux/selinux_test.go

@@ -31,9 +31,11 @@ func TestSELinux(t *testing.T) {
 		plabel, flabel = selinux.GetLxcContexts()
 		t.Log(plabel)
 		t.Log(flabel)
+		selinux.FreeLxcContexts(plabel)
 		plabel, flabel = selinux.GetLxcContexts()
 		t.Log(plabel)
 		t.Log(flabel)
+		selinux.FreeLxcContexts(plabel)
 		t.Log("getenforce ", selinux.SelinuxGetEnforce())
 		t.Log("getenforcemode ", selinux.SelinuxGetEnforceMode())
 		pid := os.Getpid()