tools/syz-linter: add custom linter

For now we have 2 simple checks:

1. for multiline comments:
/* */ -> //

2. for string len comparison with 0:
len(str) != 0 -> str != ""

Update #1876

3 files changed, 132 insertions, 0 deletions

diff --git a/tools/syz-linter/linter.go b/tools/syz-linter/linter.go
new file mode 100644
index 000000000..c4b6837b2
--- /dev/null
+++ b/tools/syz-linter/linter.go
@@ -0,0 +1,98 @@
+// Copyright 2020 syzkaller project authors. All rights reserved.
+// Use of this source code is governed by Apache 2 LICENSE that can be found in the LICENSE file.
+
+// This is our linter with custom checks for the project.
+// See the following tutorial on writing Go analyzers:
+// https://disaev.me/p/writing-useful-go-analysis-linter/
+// See the following tutorial on adding custom golangci-lint linters:
+// https://golangci-lint.run/contributing/new-linters/
+// See comments below and testdata/src/lintertest/lintertest.go for the actual checks we do.
+package main
+
+import (
+	"go/ast"
+	"go/token"
+	"strings"
+
+	"golang.org/x/tools/go/analysis"
+)
+
+var AnalyzerPlugin analyzerPlugin
+
+type analyzerPlugin struct{}
+
+func (*analyzerPlugin) GetAnalyzers() []*analysis.Analyzer {
+	return []*analysis.Analyzer{
+		SyzAnalyzer,
+	}
+}
+
+var SyzAnalyzer = &analysis.Analyzer{
+	Name: "lint",
+	Doc:  "custom syzkaller project checks",
+	Run:  run,
+}
+
+func run(pass *analysis.Pass) (interface{}, error) {
+	for _, file := range pass.Files {
+		ast.Inspect(file, func(n ast.Node) bool {
+			switch n := n.(type) {
+			case *ast.Comment:
+				checkMulitlineComments(pass, n)
+			case *ast.BinaryExpr:
+				checkStringLenCompare(pass, n)
+			}
+			return true
+		})
+	}
+	return nil, nil
+}
+
+// checkMulitlineComments warns about C++-style multiline comments.
+// We don't use them in the codebase.
+func checkMulitlineComments(pass *analysis.Pass, n *ast.Comment) {
+	if !strings.HasPrefix(n.Text, "/*") {
+		return
+	}
+	pass.Report(analysis.Diagnostic{
+		Pos:     n.Pos(),
+		Message: "Use C-style comments // instead of /* */",
+	})
+}
+
+// checkStringLenCompare checks for string len comparisons with 0.
+// E.g.: if len(str) == 0 {} should be if str == "" {}.
+func checkStringLenCompare(pass *analysis.Pass, n *ast.BinaryExpr) {
+	if n.Op != token.EQL && n.Op != token.NEQ && n.Op != token.LSS &&
+		n.Op != token.GTR && n.Op != token.LEQ && n.Op != token.GEQ {
+		return
+	}
+	if isStringLenCall(pass, n.X) && isIntZeroLiteral(n.Y) ||
+		isStringLenCall(pass, n.Y) && isIntZeroLiteral(n.X) {
+		pass.Report(analysis.Diagnostic{
+			Pos:     n.Pos(),
+			Message: "Compare string with \"\", don't compare len with 0",
+		})
+	}
+}
+
+func isStringLenCall(pass *analysis.Pass, n ast.Expr) bool {
+	call, ok := n.(*ast.CallExpr)
+	if !ok || len(call.Args) != 1 {
+		return false
+	}
+	fun, ok := call.Fun.(*ast.Ident)
+	if !ok || fun.Name != "len" {
+		return false
+	}
+	return pass.TypesInfo.Types[call.Args[0]].Type.String() == "string"
+}
+
+func isIntZeroLiteral(n ast.Expr) bool {
+	lit, ok := n.(*ast.BasicLit)
+	return ok && lit.Kind == token.INT && lit.Value == "0"
+}
+
+func main() {
+	_ = AnalyzerPlugin
+}
diff --git a/tools/syz-linter/linter_test.go b/tools/syz-linter/linter_test.go
new file mode 100644
index 000000000..a356f5cf5
--- /dev/null
+++ b/tools/syz-linter/linter_test.go
@@ -0,0 +1,15 @@
+// Copyright 2020 syzkaller project authors. All rights reserved.
+// Use of this source code is governed by Apache 2 LICENSE that can be found in the LICENSE file.
+
+package main
+
+import (
+	"testing"
+
+	"github.com/google/syzkaller/pkg/osutil"
+	"golang.org/x/tools/go/analysis/analysistest"
+)
+
+func TestLinter(t *testing.T) {
+	analysistest.Run(t, osutil.Abs("testdata"), SyzAnalyzer, "lintertest")
+}
diff --git a/tools/syz-linter/testdata/src/lintertest/lintertest.go b/tools/syz-linter/testdata/src/lintertest/lintertest.go
new file mode 100644
index 000000000..b507bc1ee
--- /dev/null
+++ b/tools/syz-linter/testdata/src/lintertest/lintertest.go
@@ -0,0 +1,19 @@
+// Copyright 2020 syzkaller project authors. All rights reserved.
+// Use of this source code is governed by Apache 2 LICENSE that can be found in the LICENSE file.
+
+package lintertest
+
+/* some comment */ // want "Use C-style comments // instead of /* */"
+var comment = 1    /* some comment */ // want "Use C-style comments // instead of /* */"
+
+func stringComparison() {
+	str := ""
+	if len(str) == 0 { // want "Compare string with \"\", don't compare len with 0"
+	}
+	if 0 != len(str) { // want "Compare string with \"\", don't compare len with 0"
+	}
+	if len(returnString()+"foo") > 0 { // want "Compare string with \"\", don't compare len with 0"
+	}
+}
+
+func returnString() string { return "foo" }