From 1cf1811d7195fe9bb436a00e335567575fac9b07 Mon Sep 17 00:00:00 2001
From: Matt Dainty <matt@bodgit-n-scarper.com>
Date: Mon, 25 Jan 2021 10:36:18 +0000
Subject: [PATCH] ssh: use the correct token from the client

This fixes the case where AcceptSecContext is always called with the
first token sent by the client instead of the most recently sent one.
Previously, despite being being read from the client and unmarshalled,
it was never actually used.

Fixes golang/go#43875

Change-Id: I1967d9a107af03d6778a9437b48e785d61710ee5
GitHub-Last-Rev: 0d58e4d50014fac0a9ea1eef85489172137eb8aa
GitHub-Pull-Request: golang/crypto#176
Reviewed-on: https://go-review.googlesource.com/c/crypto/+/286252
Run-TryBot: Filippo Valsorda <filippo@golang.org>
Auto-Submit: Filippo Valsorda <filippo@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Run-TryBot: Nicola Murino <nicola.murino@gmail.com>
Reviewed-by: Nicola Murino <nicola.murino@gmail.com>
Reviewed-by: Filippo Valsorda <filippo@golang.org>
Reviewed-by: Than McIntosh <thanm@google.com>
---
 ssh/server.go | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/ssh/server.go b/ssh/server.go
index 8f1505af94..7f0c236a9a 100644
--- a/ssh/server.go
+++ b/ssh/server.go
@@ -337,7 +337,7 @@ func checkSourceAddress(addr net.Addr, sourceAddrs string) error {
 	return fmt.Errorf("ssh: remote address %v is not allowed because of source-address restriction", addr)
 }
 
-func gssExchangeToken(gssapiConfig *GSSAPIWithMICConfig, firstToken []byte, s *connection,
+func gssExchangeToken(gssapiConfig *GSSAPIWithMICConfig, token []byte, s *connection,
 	sessionID []byte, userAuthReq userAuthRequestMsg) (authErr error, perms *Permissions, err error) {
 	gssAPIServer := gssapiConfig.Server
 	defer gssAPIServer.DeleteSecContext()
@@ -347,7 +347,7 @@ func gssExchangeToken(gssapiConfig *GSSAPIWithMICConfig, firstToken []byte, s *c
 			outToken     []byte
 			needContinue bool
 		)
-		outToken, srcName, needContinue, err = gssAPIServer.AcceptSecContext(firstToken)
+		outToken, srcName, needContinue, err = gssAPIServer.AcceptSecContext(token)
 		if err != nil {
 			return err, nil, nil
 		}
@@ -369,6 +369,7 @@ func gssExchangeToken(gssapiConfig *GSSAPIWithMICConfig, firstToken []byte, s *c
 		if err := Unmarshal(packet, userAuthGSSAPITokenReq); err != nil {
 			return nil, nil, err
 		}
+		token = userAuthGSSAPITokenReq.Token
 	}
 	packet, err := s.transport.readPacket()
 	if err != nil {