From 7131c7d40d4f5bd32b16031e884153548eee133f Mon Sep 17 00:00:00 2001
From: spacetourist <guy.callum@gmail.com>
Date: Sat, 21 Oct 2017 14:13:41 +0100
Subject: [PATCH] Configurable SSH cipher suite (#913)

* Configurable SSH cipher suite

* Update configuration file comment

* Add default in settings loading code

* Fix fmt and log messsage

* Remove default from code as this could probably might not be good idea
---
 conf/app.ini               | 3 +++
 modules/setting/setting.go | 2 ++
 modules/ssh/ssh.go         | 5 ++++-
 routers/init.go            | 4 ++--
 4 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/conf/app.ini b/conf/app.ini
index 6524486b82..3b1bccf816 100644
--- a/conf/app.ini
+++ b/conf/app.ini
@@ -125,6 +125,9 @@ SSH_PORT = 22
 SSH_LISTEN_PORT = %(SSH_PORT)s
 ; Root path of SSH directory, default is '~/.ssh', but you have to use '/home/git/.ssh'.
 SSH_ROOT_PATH =
+; For built-in SSH server only, choose the ciphers to support for SSH connections,
+; for system SSH this setting has no effect
+SSH_SERVER_CIPHERS = aes128-ctr, aes192-ctr, aes256-ctr, aes128-gcm@openssh.com, arcfour256, arcfour128
 ; Directory to create temporary files when test public key using ssh-keygen,
 ; default is system temporary directory.
 SSH_KEY_TEST_PATH =
diff --git a/modules/setting/setting.go b/modules/setting/setting.go
index 0bd73b8cba..0be95daadd 100644
--- a/modules/setting/setting.go
+++ b/modules/setting/setting.go
@@ -96,6 +96,7 @@ var (
 		ListenHost           string         `ini:"SSH_LISTEN_HOST"`
 		ListenPort           int            `ini:"SSH_LISTEN_PORT"`
 		RootPath             string         `ini:"SSH_ROOT_PATH"`
+		ServerCiphers        []string       `ini:"SSH_SERVER_CIPHERS"`
 		KeyTestPath          string         `ini:"SSH_KEY_TEST_PATH"`
 		KeygenPath           string         `ini:"SSH_KEYGEN_PATH"`
 		AuthorizedKeysBackup bool           `ini:"SSH_AUTHORIZED_KEYS_BACKUP"`
@@ -708,6 +709,7 @@ func NewContext() {
 		SSH.Domain = Domain
 	}
 	SSH.RootPath = path.Join(homeDir, ".ssh")
+	SSH.ServerCiphers = sec.Key("SSH_SERVER_CIPHERS").Strings(",")
 	SSH.KeyTestPath = os.TempDir()
 	if err = Cfg.Section("server").MapTo(&SSH); err != nil {
 		log.Fatal(4, "Failed to map SSH settings: %v", err)
diff --git a/modules/ssh/ssh.go b/modules/ssh/ssh.go
index 36a383fa86..62edaf15bc 100644
--- a/modules/ssh/ssh.go
+++ b/modules/ssh/ssh.go
@@ -151,8 +151,11 @@ func listen(config *ssh.ServerConfig, host string, port int) {
 }
 
 // Listen starts a SSH server listens on given port.
-func Listen(host string, port int) {
+func Listen(host string, port int, ciphers []string) {
 	config := &ssh.ServerConfig{
+		Config: ssh.Config{
+			Ciphers: ciphers,
+		},
 		PublicKeyCallback: func(conn ssh.ConnMetadata, key ssh.PublicKey) (*ssh.Permissions, error) {
 			pkey, err := models.SearchPublicKeyByContent(strings.TrimSpace(string(ssh.MarshalAuthorizedKey(key))))
 			if err != nil {
diff --git a/routers/init.go b/routers/init.go
index d04ffea4c1..006f285266 100644
--- a/routers/init.go
+++ b/routers/init.go
@@ -77,7 +77,7 @@ func GlobalInit() {
 	checkRunMode()
 
 	if setting.InstallLock && setting.SSH.StartBuiltinServer {
-		ssh.Listen(setting.SSH.ListenHost, setting.SSH.ListenPort)
-		log.Info("SSH server started on %s:%v", setting.SSH.ListenHost, setting.SSH.ListenPort)
+		ssh.Listen(setting.SSH.ListenHost, setting.SSH.ListenPort, setting.SSH.ServerCiphers)
+		log.Info("SSH server started on %s:%d. Cipher list (%v)", setting.SSH.ListenHost, setting.SSH.ListenPort, setting.SSH.ServerCiphers)
 	}
 }