plumbing/transport: ssh check if list of known_hosts files is empty

Signed-off-by: kuba-- <kuba@sourced.tech>

Author: kuba--

plumbing/transport/ssh/auth_method.go

@@ -236,21 +236,23 @@ func (a *PublicKeysCallback) ClientConfig() (*ssh.ClientConfig, error) {
 // NewKnownHostsCallback returns ssh.HostKeyCallback based on a file based on a
 // known_hosts file. http://man.openbsd.org/sshd#SSH_KNOWN_HOSTS_FILE_FORMAT
 //
-// If files is empty, the list of files will be read from the SSH_KNOWN_HOSTS
+// If list of files is empty, then it will be read from the SSH_KNOWN_HOSTS
 // environment variable, example:
 //   /home/foo/custom_known_hosts_file:/etc/custom_known/hosts_file
 //
 // If SSH_KNOWN_HOSTS is not set the following file locations will be used:
 //   ~/.ssh/known_hosts
 //   /etc/ssh/ssh_known_hosts
 func NewKnownHostsCallback(files ...string) (ssh.HostKeyCallback, error) {
-	files, err := getDefaultKnownHostsFiles()
-	if err != nil {
-		return nil, err
+	var err error
+
+	if len(files) == 0 {
+		if files, err = getDefaultKnownHostsFiles(); err != nil {
+			return nil, err
+		}
 	}
 
-	files, err = filterKnownHostsFiles(files...)
-	if err != nil {
+	if files, err = filterKnownHostsFiles(files...); err != nil {
 		return nil, err
 	}
 

plumbing/transport/ssh/auth_method_test.go

@@ -1,16 +1,30 @@
 package ssh
 
 import (
+	"bufio"
 	"fmt"
 	"io/ioutil"
 	"os"
+	"strings"
 
+	"golang.org/x/crypto/ssh"
 	"golang.org/x/crypto/ssh/testdata"
 
 	. "gopkg.in/check.v1"
 )
 
-type SuiteCommon struct{}
+type (
+	SuiteCommon struct{}
+
+	mockKnownHosts struct{}
+)
+
+func (mockKnownHosts) host() string { return "github.com" }
+func (mockKnownHosts) knownHosts() []byte {
+	return []byte(`github.com ssh-rsa AAAAB3NzaC1yc2EAAAABIwAAAQEAq2A7hRGmdnm9tUDbO9IDSwBK6TbQa+PXYPCPy6rbTrTtw7PHkccKrpp0yVhp5HdEIcKr6pLlVDBfOLX9QUsyCOV0wzfjIJNlGEYsdlLJizHhbn2mUjvSAHQqZETYP81eFzLQNnPHt4EVVUh7VfDESU84KezmD5QlWpXLmvU31/yMf+Se8xhHTvKSCZIFImWwoG6mbUoWf9nzpIoaSjB+weqqUUmpaaasXVal72J+UX2B+2RPW3RcT0eOzQgqlJL3RKrTJvdsjE3JEAvGq3lGHSZXy28G3skua2SmVi/w4yCE6gbODqnTWlg7+wC604ydGXA8VJiS5ap43JXiUFFAaQ==`)
+}
+func (mockKnownHosts) Network() string { return "tcp" }
+func (mockKnownHosts) String() string  { return "github.com:22" }
 
 var _ = Suite(&SuiteCommon{})
 
@@ -149,3 +163,49 @@ func (*SuiteCommon) TestNewPublicKeysWithInvalidPEM(c *C) {
 	c.Assert(err, NotNil)
 	c.Assert(auth, IsNil)
 }
+
+func (*SuiteCommon) TestNewKnownHostsCallback(c *C) {
+	var mock = mockKnownHosts{}
+
+	f, err := ioutil.TempFile("", "known-hosts")
+	c.Assert(err, IsNil)
+
+	_, err = f.Write(mock.knownHosts())
+	c.Assert(err, IsNil)
+
+	err = f.Close()
+	c.Assert(err, IsNil)
+
+	defer os.RemoveAll(f.Name())
+
+	f, err = os.Open(f.Name())
+	c.Assert(err, IsNil)
+
+	defer f.Close()
+
+	var hostKey ssh.PublicKey
+	scanner := bufio.NewScanner(f)
+	for scanner.Scan() {
+		fields := strings.Split(scanner.Text(), " ")
+		if len(fields) != 3 {
+			continue
+		}
+		if strings.Contains(fields[0], mock.host()) {
+			var err error
+			hostKey, _, _, _, err = ssh.ParseAuthorizedKey(scanner.Bytes())
+			if err != nil {
+				c.Fatalf("error parsing %q: %v", fields[2], err)
+			}
+			break
+		}
+	}
+	if hostKey == nil {
+		c.Fatalf("no hostkey for %s", mock.host())
+	}
+
+	clb, err := NewKnownHostsCallback(f.Name())
+	c.Assert(err, IsNil)
+
+	err = clb(mock.String(), mock, hostKey)
+	c.Assert(err, IsNil)
+}