From df3a98214148db0f499ae4ab32bc81cbac716a25 Mon Sep 17 00:00:00 2001
From: lyc8503 <36782264+lyc8503@users.noreply.github.com>
Date: Wed, 8 Feb 2023 16:20:48 +0800
Subject: [PATCH] Add SSH outbound host key validation

---
 docs/configuration/outbound/ssh.md    |  7 +++++++
 docs/configuration/outbound/ssh.zh.md |  7 +++++++
 option/ssh.go                         |  1 +
 outbound/ssh.go                       | 23 ++++++++++++++++++++++-
 4 files changed, 37 insertions(+), 1 deletion(-)

diff --git a/docs/configuration/outbound/ssh.md b/docs/configuration/outbound/ssh.md
index cf948f45..1384f8dd 100644
--- a/docs/configuration/outbound/ssh.md
+++ b/docs/configuration/outbound/ssh.md
@@ -12,6 +12,9 @@
   "private_key": "",
   "private_key_path": "$HOME/.ssh/id_rsa",
   "private_key_passphrase": "",
+  "host_key": [
+    "ecdsa-sha2-nistp256 AAAAE2VjZHNhLXNoYTItbmlzdH..."
+  ],
   "host_key_algorithms": [],
   "client_version": "SSH-2.0-OpenSSH_7.4p1",
 
@@ -51,6 +54,10 @@ Private key path.
 
 Private key passphrase.
 
+#### host_key
+
+Host key. Accept any if empty.
+
 #### host_key_algorithms
 
 Host key algorithms.
diff --git a/docs/configuration/outbound/ssh.zh.md b/docs/configuration/outbound/ssh.zh.md
index e14e9fd4..e538e64a 100644
--- a/docs/configuration/outbound/ssh.zh.md
+++ b/docs/configuration/outbound/ssh.zh.md
@@ -12,6 +12,9 @@
   "private_key": "",
   "private_key_path": "$HOME/.ssh/id_rsa",
   "private_key_passphrase": "",
+  "host_key": [
+    "ecdsa-sha2-nistp256 AAAAE2VjZHNhLXNoYTItbmlzdH..."
+  ],
   "host_key_algorithms": [],
   "client_version": "SSH-2.0-OpenSSH_7.4p1",
 
@@ -51,6 +54,10 @@ SSH 用户, 默认使用 root。
 
 密钥密码。
 
+#### host_key
+
+主机密钥，留空接受所有。
+
 #### host_key_algorithms
 
 主机密钥算法。
diff --git a/option/ssh.go b/option/ssh.go
index 30321705..1f25caf8 100644
--- a/option/ssh.go
+++ b/option/ssh.go
@@ -8,6 +8,7 @@ type SSHOutboundOptions struct {
 	PrivateKey           string           `json:"private_key,omitempty"`
 	PrivateKeyPath       string           `json:"private_key_path,omitempty"`
 	PrivateKeyPassphrase string           `json:"private_key_passphrase,omitempty"`
+	HostKey              Listable[string] `json:"host_key,omitempty"`
 	HostKeyAlgorithms    Listable[string] `json:"host_key_algorithms,omitempty"`
 	ClientVersion        string           `json:"client_version,omitempty"`
 }
diff --git a/outbound/ssh.go b/outbound/ssh.go
index 33579a7e..ad1ca2e3 100644
--- a/outbound/ssh.go
+++ b/outbound/ssh.go
@@ -1,7 +1,9 @@
 package outbound
 
 import (
+	"bytes"
 	"context"
+	"encoding/base64"
 	"math/rand"
 	"net"
 	"os"
@@ -32,6 +34,7 @@ type SSH struct {
 	dialer            N.Dialer
 	serverAddr        M.Socksaddr
 	user              string
+	hostKey           []ssh.PublicKey
 	hostKeyAlgorithms []string
 	clientVersion     string
 	authMethod        []ssh.AuthMethod
@@ -91,6 +94,15 @@ func NewSSH(ctx context.Context, router adapter.Router, logger log.ContextLogger
 		}
 		outbound.authMethod = append(outbound.authMethod, ssh.PublicKeys(signer))
 	}
+	if len(options.HostKey) > 0 {
+		for _, hostKey := range options.HostKey {
+			key, _, _, _, err := ssh.ParseAuthorizedKey([]byte(hostKey))
+			if err != nil {
+				return nil, E.New("parse host key ", key)
+			}
+			outbound.hostKey = append(outbound.hostKey, key)
+		}
+	}
 	return outbound, nil
 }
 
@@ -126,7 +138,16 @@ func (s *SSH) connect() (*ssh.Client, error) {
 		ClientVersion:     s.clientVersion,
 		HostKeyAlgorithms: s.hostKeyAlgorithms,
 		HostKeyCallback: func(hostname string, remote net.Addr, key ssh.PublicKey) error {
-			return nil
+			if len(s.hostKey) == 0 {
+				return nil
+			}
+			serverKey := key.Marshal()
+			for _, hostKey := range s.hostKey {
+				if bytes.Equal(serverKey, hostKey.Marshal()) {
+					return nil
+				}
+			}
+			return E.New("host key mismatch, server send ", key.Type(), " ", base64.StdEncoding.EncodeToString(serverKey))
 		},
 	}
 	clientConn, chans, reqs, err := ssh.NewClientConn(conn, s.serverAddr.Addr.String(), config)