Allow numeric groups for containers without /etc/group

/etc/groups is not needed when specifying numeric group ids. This
change allows containers without /etc/groups to specify numeric
supplemental groups.

Signed-off-by: Sami Wagiaalla <swagiaal@redhat.com>

libcontainer/user/user.go

@@ -349,21 +349,26 @@ func GetExecUser(userSpec string, defaults *ExecUser, passwd, group io.Reader) (
 	return user, nil
 }
 
-// GetAdditionalGroups looks up a list of groups by name or group id against
-// against the given /etc/group formatted data. If a group name cannot be found,
-// an error will be returned. If a group id cannot be found, it will be returned
-// as-is.
+// GetAdditionalGroups looks up a list of groups by name or group id
+// against the given /etc/group formatted data. If a group name cannot
+// be found, an error will be returned. If a group id cannot be found,
+// or the given group data is nil, the id will be returned as-is
+// provided it is in the legal range.
 func GetAdditionalGroups(additionalGroups []string, group io.Reader) ([]int, error) {
-	groups, err := ParseGroupFilter(group, func(g Group) bool {
-		for _, ag := range additionalGroups {
-			if g.Name == ag || strconv.Itoa(g.Gid) == ag {
-				return true
+	var groups = []Group{}
+	if group != nil {
+		var err error
+		groups, err = ParseGroupFilter(group, func(g Group) bool {
+			for _, ag := range additionalGroups {
+				if g.Name == ag || strconv.Itoa(g.Gid) == ag {
+					return true
+				}
 			}
+			return false
+		})
+		if err != nil {
+			return nil, fmt.Errorf("Unable to find additional groups %v: %v", additionalGroups, err)
 		}
-		return false
-	})
-	if err != nil {
-		return nil, fmt.Errorf("Unable to find additional groups %v: %v", additionalGroups, err)
 	}
 
 	gidMap := make(map[int]struct{})
@@ -401,13 +406,13 @@ func GetAdditionalGroups(additionalGroups []string, group io.Reader) ([]int, err
 	return gids, nil
 }
 
-// Wrapper around GetAdditionalGroups that opens the groupPath given and gives
-// it as an argument to GetAdditionalGroups.
+// GetAdditionalGroupsPath is a wrapper around GetAdditionalGroups
+// that opens the groupPath given and gives it as an argument to
+// GetAdditionalGroups.
 func GetAdditionalGroupsPath(additionalGroups []string, groupPath string) ([]int, error) {
 	group, err := os.Open(groupPath)
-	if err != nil {
-		return nil, fmt.Errorf("Failed to open group file: %v", err)
+	if err == nil {
+		defer group.Close()
 	}
-	defer group.Close()
 	return GetAdditionalGroups(additionalGroups, group)
 }

libcontainer/user/user_test.go

@@ -434,3 +434,39 @@ this is just some garbage data
 		}
 	}
 }
+
+func TestGetAdditionalGroupsNumeric(t *testing.T) {
+	tests := []struct {
+		groups   []string
+		expected []int
+		hasError bool
+	}{
+		{
+			// numeric groups only
+			groups:   []string{"1234", "5678"},
+			expected: []int{1234, 5678},
+		},
+		{
+			// numeric and alphabetic
+			groups:   []string{"1234", "fake"},
+			expected: nil,
+			hasError: true,
+		},
+	}
+
+	for _, test := range tests {
+		gids, err := GetAdditionalGroups(test.groups, nil)
+		if test.hasError && err == nil {
+			t.Errorf("Parse(%#v) expects error but has none", test)
+			continue
+		}
+		if !test.hasError && err != nil {
+			t.Errorf("Parse(%#v) has error %v", test, err)
+			continue
+		}
+		sort.Sort(sort.IntSlice(gids))
+		if !reflect.DeepEqual(gids, test.expected) {
+			t.Errorf("Gids(%v), expect %v from groups %v", gids, test.expected, test.groups)
+		}
+	}
+}