Added fuzzer for frontend dockerfile parser

Makefile

@@ -18,6 +18,9 @@ clean: FORCE
 test:
 	./hack/test integration gateway dockerfile
 
+fuzz:
+	./hack/fuzz
+
 lint:
 	./hack/lint
 

hack/dockerfiles/fuzz.Dockerfile

@@ -0,0 +1,15 @@
+FROM golang:1.15-alpine
+ENV DEBIAN_FRONTEND=noninteractive
+
+RUN mkdir /root/src
+ENV GOPATH /root/go
+ENV GOROOT /usr/local/go
+ENV PATH $PATH:/usr/local/go/bin
+
+RUN apk add --no-cache git mercurial \
+    && go get -u github.com/dvyukov/go-fuzz/go-fuzz \
+    github.com/dvyukov/go-fuzz/go-fuzz-build \
+    github.com/moby/buildkit \
+    && apk del git mercurial
+#RUN cd $GOPATH/src/github.com/moby/buildkit/util/testutil/fuzz \
+#    && $GOPATH/bin/go-fuzz-build && $GOPATH/bin/go-fuzz

hack/fuzz

@@ -0,0 +1,3 @@
+#!/usr/bin/env bash
+
+cd hack/dockerfiles && sudo docker build -f fuzz.Dockerfile .

util/testutil/fuzz/fuzz.go

@@ -0,0 +1,17 @@
+// +build gofuzz
+
+package fuzz
+
+import (
+	"bytes"
+
+	"github.com/moby/buildkit/frontend/dockerfile/parser"
+)
+
+func Fuzz(data []byte) int {
+	_, err := parser.Parse(bytes.NewReader(data))
+	if err != nil {
+		return 0
+	}
+	return 1
+}