Allow . in the usernames of create-user

LP: #1603018

osutil/user.go

@@ -26,13 +26,21 @@ import (
 	"os/exec"
 	"os/user"
 	"path/filepath"
+	"regexp"
 	"strings"
 )
 
 var userLookup = user.Lookup
 
 func AddExtraUser(name string, sshKeys []string, gecos string) error {
-	cmd := exec.Command("adduser", "--gecos", gecos, "--extrausers", "--disabled-password", name)
+	// we check the (user)name ourselfs, adduser is a bit too
+	// strict (i.e. no `.`)
+	validNames := regexp.MustCompile(`^[a-z][-a-z0-9_.]*$`)
+	if !validNames.MatchString(name) {
+		return fmt.Errorf("cannot add user %q: name contains invalid charackters", name)
+	}
+
+	cmd := exec.Command("adduser", "--force-badname", "--gecos", gecos, "--extrausers", "--disabled-password", name)
 	if output, err := cmd.CombinedOutput(); err != nil {
 		return fmt.Errorf("adduser failed with %s: %s", err, output)
 	}

osutil/user_test.go

@@ -52,9 +52,14 @@ func (s *createUserSuite) TestAddExtraUser(c *check.C) {
 	err := osutil.AddExtraUser("karl", []string{"ssh-key1", "ssh-key2"}, "my gecos")
 	c.Assert(err, check.IsNil)
 	c.Check(mc.Calls(), check.DeepEquals, [][]string{
-		{"adduser", "--gecos", "my gecos", "--extrausers", "--disabled-password", "karl"},
+		{"adduser", "--force-badname", "--gecos", "my gecos", "--extrausers", "--disabled-password", "karl"},
 	})
 	sshKeys, err := ioutil.ReadFile(filepath.Join(mockHome, ".ssh", "authorized_keys"))
 	c.Assert(err, check.IsNil)
 	c.Check(string(sshKeys), check.Equals, "ssh-key1\nssh-key2")
 }
+
+func (s *createUserSuite) TestAddExtraUserInvalid(c *check.C) {
+	err := osutil.AddExtraUser("k!", nil, "my gecos")
+	c.Assert(err, check.ErrorMatches, `cannot add user "k!": name contains invalid charackters`)
+}