cmd/go: reject relative tmpdir

Fixes #23264

Change-Id: Ib6c343dc8e32949c6de72cb628cace2e8fabc302
Reviewed-on: https://go-review.googlesource.com/103236
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/cmd/go/go_test.go

@@ -5991,3 +5991,26 @@ func TestDontReportRemoveOfEmptyDir(t *testing.T) {
 		t.Error("unnecessary output when installing installed package")
 	}
 }
+
+// Issue 23264.
+func TestNoRelativeTmpdir(t *testing.T) {
+	tg := testgo(t)
+	defer tg.cleanup()
+
+	tg.tempFile("src/a/a.go", `package a`)
+	tg.cd(tg.path("."))
+	tg.must(os.Mkdir("tmp", 0777))
+
+	tg.setenv("GOCACHE", "off")
+	tg.setenv("GOPATH", tg.path("."))
+	tg.setenv("GOTMPDIR", "tmp")
+	tg.runFail("build", "a")
+	tg.grepStderr("relative tmpdir", "wrong error")
+
+	if runtime.GOOS != "windows" && runtime.GOOS != "plan9" {
+		tg.unsetenv("GOTMPDIR")
+		tg.setenv("TMPDIR", "tmp")
+		tg.runFail("build", "a")
+		tg.grepStderr("relative tmpdir", "wrong error")
+	}
+}

src/cmd/go/internal/work/action.go

@@ -223,6 +223,10 @@ func (b *Builder) Init() {
 		if err != nil {
 			base.Fatalf("%s", err)
 		}
+		if !filepath.IsAbs(b.WorkDir) {
+			os.RemoveAll(b.WorkDir)
+			base.Fatalf("cmd/go: relative tmpdir not supported")
+		}
 		if cfg.BuildX || cfg.BuildWork {
 			fmt.Fprintf(os.Stderr, "WORK=%s\n", b.WorkDir)
 		}