scc sort by priority

api/swagger-spec/api-v1.json

@@ -14741,6 +14741,7 @@
    "v1.SecurityContextConstraints": {
     "id": "v1.SecurityContextConstraints",
     "required": [
+     "priority",
      "allowPrivilegedContainer",
      "allowedCapabilities",
      "allowHostDirVolumePlugin",
@@ -14761,6 +14762,11 @@
      "metadata": {
       "$ref": "v1.ObjectMeta"
      },
+     "priority": {
+      "type": "integer",
+      "format": "int32",
+      "description": "determines which SCC is used when multiple SCCs allow a particular pod; higher priority SCCs are preferred"
+     },
      "allowPrivilegedContainer": {
       "type": "boolean",
       "description": "allow containers to run as privileged"

pkg/cmd/server/bootstrappolicy/securitycontextconstraints.go

@@ -246,6 +246,8 @@ func GetBootstrapSecurityContextConstraints(sccNameToAdditionalGroups map[string
 			SupplementalGroups: kapi.SupplementalGroupsStrategyOptions{
 				Type: kapi.SupplementalGroupsStrategyRunAsAny,
 			},
+			// prefer the anyuid SCC over ones that force a uid
+			Priority: 1,
 		},
 	}
 

pkg/security/admission/admission.go

@@ -127,7 +127,7 @@ func (c *constraint) Admit(a kadmission.Attributes) error {
 
 	// remove duplicate constraints and sort
 	matchedConstraints = deduplicateSecurityContextConstraints(matchedConstraints)
-	sort.Sort(ByRestrictions(matchedConstraints))
+	sort.Sort(ByPriority(matchedConstraints))
 	providers, errs := c.createProvidersFromConstraints(a.GetNamespace(), matchedConstraints)
 	logProviders(pod, providers, errs)
 

pkg/security/admission/admission_test.go

@@ -70,7 +70,7 @@ func TestAdmit(t *testing.T) {
 		Groups: []string{"system:serviceaccounts"},
 	}
 	// create scc that has specific requirements that shouldn't match but is permissioned to
-	// service accounts to test exact matches
+	// service accounts to test that we're matching first against the higher priority SCC.
 	var exactUID int64 = 999
 	saExactSCC := &kapi.SecurityContextConstraints{
 		ObjectMeta: kapi.ObjectMeta{

pkg/security/admission/bypriority.go

@@ -0,0 +1,44 @@
+package admission
+
+import (
+	kapi "k8s.io/kubernetes/pkg/api"
+)
+
+// ByRestrictions is a helper to sort SCCs based on priority.  If priorities are equal
+// a string compare of the name is used.
+type ByPriority []*kapi.SecurityContextConstraints
+
+func (s ByPriority) Len() int {
+	return len(s)
+}
+func (s ByPriority) Swap(i, j int) { s[i], s[j] = s[j], s[i] }
+func (s ByPriority) Less(i, j int) bool {
+	iSCC := s[i]
+	jSCC := s[j]
+
+	// a higher priority is considered "less" so that it moves to the front of the line
+	if iSCC.Priority > jSCC.Priority {
+		return true
+	}
+
+	if iSCC.Priority < jSCC.Priority {
+		return false
+	}
+
+	// they are equal, let's try point values
+	iRestrictionScore := pointValue(iSCC)
+	jRestrictionScore := pointValue(jSCC)
+
+	// a lower restriction score is considered "less" so that it moves to the front of the line
+	// (the greater the score, the more lax the SCC is)
+	if iRestrictionScore < jRestrictionScore {
+		return true
+	}
+
+	if iRestrictionScore > jRestrictionScore {
+		return false
+	}
+
+	// they are still equal, sort by name
+	return iSCC.Name < jSCC.Name
+}

pkg/security/admission/bypriority_test.go

@@ -0,0 +1,86 @@
+package admission
+
+import (
+	"sort"
+	"testing"
+
+	kapi "k8s.io/kubernetes/pkg/api"
+)
+
+func TestByPriority(t *testing.T) {
+	sccs := []*kapi.SecurityContextConstraints{testSCC("one", 1), testSCC("two", 2), testSCC("three", 3), testSCC("negative", -1), testSCC("super", 100)}
+	expected := []string{"super", "three", "two", "one", "negative"}
+
+	sort.Sort(ByPriority(sccs))
+
+	for i, scc := range sccs {
+		if scc.Name != expected[i] {
+			t.Errorf("sort by priority found %s at element %d but expected %s", scc.Name, i, expected[i])
+		}
+	}
+}
+
+func TestByPrioritiesScore(t *testing.T) {
+	privilegedSCC := testSCC("privileged", 1)
+	privilegedSCC.AllowPrivilegedContainer = true
+
+	nonPriviledSCC := testSCC("nonprivileged", 1)
+
+	hostDirSCC := testSCC("hostdir", 1)
+	hostDirSCC.AllowHostDirVolumePlugin = true
+
+	sccs := []*kapi.SecurityContextConstraints{nonPriviledSCC, privilegedSCC, hostDirSCC}
+	// with equal priorities expect that the SCCs will be sorted with hold behavior based on their score,
+	// most restrictive first
+	expected := []string{"nonprivileged", "hostdir", "privileged"}
+
+	sort.Sort(ByPriority(sccs))
+
+	for i, scc := range sccs {
+		if scc.Name != expected[i] {
+			t.Errorf("sort by score found %s at element %d but expected %s", scc.Name, i, expected[i])
+		}
+	}
+}
+
+func TestByPrioritiesName(t *testing.T) {
+	sccs := []*kapi.SecurityContextConstraints{testSCC("e", 1), testSCC("d", 1), testSCC("a", 1), testSCC("c", 1), testSCC("b", 1)}
+	// expect that with equal priorities AND an equal point value that SCCs are sorted by name
+	expected := []string{"a", "b", "c", "d", "e"}
+
+	sort.Sort(ByPriority(sccs))
+
+	for i, scc := range sccs {
+		if scc.Name != expected[i] {
+			t.Errorf("sort by priority found %s at element %d but expected %s", scc.Name, i, expected[i])
+		}
+	}
+}
+
+func TestByPrioritiesMixedSCCs(t *testing.T) {
+	privilegedSCC := testSCC("privileged", 1)
+	privilegedSCC.AllowPrivilegedContainer = true
+
+	nonPriviledSCC := testSCC("nonprivileged", 1)
+
+	sccs := []*kapi.SecurityContextConstraints{testSCC("priorityB", 5), testSCC("priorityA", 5), testSCC("super", 100), privilegedSCC, nonPriviledSCC}
+	// highest priority first, equal priority and equal score sorted by name, equal priority and non-equal score sorted most restrictive to least.
+	expected := []string{"super", "priorityA", "priorityB", "nonprivileged", "privileged"}
+
+	sort.Sort(ByPriority(sccs))
+
+	for i, scc := range sccs {
+		if scc.Name != expected[i] {
+			t.Errorf("sort by priority found %s at element %d but expected %s", scc.Name, i, expected[i])
+		}
+	}
+}
+
+func testSCC(name string, priority int) *kapi.SecurityContextConstraints {
+	return &kapi.SecurityContextConstraints{
+		ObjectMeta: kapi.ObjectMeta{
+			Name: name,
+		},
+		Priority: priority,
+	}
+}

pkg/security/admission/byrestrictions.go

@@ -12,12 +12,12 @@ func (s ByRestrictions) Len() int {
 }
 func (s ByRestrictions) Swap(i, j int) { s[i], s[j] = s[j], s[i] }
 func (s ByRestrictions) Less(i, j int) bool {
-	return s.pointValue(s[i]) < s.pointValue(s[j])
+	return pointValue(s[i]) < pointValue(s[j])
 }
 
 // pointValue places a value on the SCC based on the settings of the SCC that can be used
 // to determine how restrictive it is.  The lower the number, the more restrictive it is.
-func (s ByRestrictions) pointValue(constraint *kapi.SecurityContextConstraints) int {
+func pointValue(constraint *kapi.SecurityContextConstraints) int {
 	points := 0
 
 	// make sure these are always valued higher than the combination of the highest strategies