make sshContext thread safe and fix the data race bug

Author: wxiaoguang

context.go

@@ -94,11 +94,14 @@ type Context interface {
 type sshContext struct {
 	context.Context
 	*sync.Mutex
+
+	values   map[interface{}]interface{}
+	valuesMu sync.Mutex
 }
 
 func newContext(srv *Server) (*sshContext, context.CancelFunc) {
 	innerCtx, cancel := context.WithCancel(context.Background())
-	ctx := &sshContext{innerCtx, &sync.Mutex{}}
+	ctx := &sshContext{Context: innerCtx, Mutex: &sync.Mutex{}, values: make(map[interface{}]interface{})}
 	ctx.SetValue(ContextKeyServer, srv)
 	perms := &Permissions{&gossh.Permissions{}}
 	ctx.SetValue(ContextKeyPermissions, perms)
@@ -119,8 +122,19 @@ func applyConnMetadata(ctx Context, conn gossh.ConnMetadata) {
 	ctx.SetValue(ContextKeyRemoteAddr, conn.RemoteAddr())
 }
 
+func (ctx *sshContext) Value(key interface{}) interface{} {
+	ctx.valuesMu.Lock()
+	defer ctx.valuesMu.Unlock()
+	if v, ok := ctx.values[key]; ok {
+		return v
+	}
+	return ctx.Context.Value(key)
+}
+
 func (ctx *sshContext) SetValue(key, value interface{}) {
-	ctx.Context = context.WithValue(ctx.Context, key, value)
+	ctx.valuesMu.Lock()
+	defer ctx.valuesMu.Unlock()
+	ctx.values[key] = value
 }
 
 func (ctx *sshContext) User() string {

context_test.go

@@ -1,6 +1,9 @@
 package ssh
 
-import "testing"
+import (
+	"testing"
+	"time"
+)
 
 func TestSetPermissions(t *testing.T) {
 	t.Parallel()
@@ -45,3 +48,38 @@ func TestSetValue(t *testing.T) {
 		t.Fatal(err)
 	}
 }
+
+func TestSetValueConcurrency(t *testing.T) {
+	ctx, cancel := newContext(nil)
+	defer cancel()
+
+	go func() {
+		for { // use a loop to access context.Context functions to make sure they are thread-safe with SetValue
+			_, _ = ctx.Deadline()
+			_ = ctx.Err()
+			_ = ctx.Value("foo")
+			select {
+			case <-ctx.Done():
+				break
+			default:
+			}
+		}
+	}()
+	ctx.SetValue("bar", -1) // a context value which never changes
+	now := time.Now()
+	var cnt int64
+	go func() {
+		for time.Since(now) < 100*time.Millisecond {
+			cnt++
+			ctx.SetValue("foo", cnt) // a context value which changes a lot
+		}
+		cancel()
+	}()
+	<-ctx.Done()
+	if ctx.Value("foo") != cnt {
+		t.Fatal("context.Value(foo) doesn't match latest SetValue")
+	}
+	if ctx.Value("bar") != -1 {
+		t.Fatal("context.Value(bar) doesn't match latest SetValue")
+	}
+}