cmd/go: sanitize go env outputs

go env, without any arguments, outputs the environment variables in
the form of a script that can be run on the host OS. On Unix, single
quote the strings and place single quotes themselves outside the
single quoted strings. On windows use the set "var=val" syntax with
the quote starting before the variable.

Fixes #58508

Change-Id: Iecd379a4af7285ea9b2024f0202250c74fd9a2bd
Reviewed-on: https://go-review.googlesource.com/c/go/+/488375
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Michael Matloob <matloob@golang.org>
Reviewed-by: Damien Neil <dneil@google.com>
Run-TryBot: Michael Matloob <matloob@golang.org>
Reviewed-by: Bryan Mills <bcmills@google.com>
Reviewed-by: Quim Muntal <quimmuntal@gmail.com>

src/cmd/go/internal/envcmd/env.go

@@ -6,6 +6,7 @@
 package envcmd
 
 import (
+	"bytes"
 	"context"
 	"encoding/json"
 	"fmt"
@@ -17,6 +18,7 @@ import (
 	"runtime"
 	"sort"
 	"strings"
+	"unicode"
 	"unicode/utf8"
 
 	"cmd/go/internal/base"
@@ -413,9 +415,12 @@ func checkBuildConfig(add map[string]string, del map[string]bool) error {
 func PrintEnv(w io.Writer, env []cfg.EnvVar) {
 	for _, e := range env {
 		if e.Name != "TERM" {
+			if runtime.GOOS != "plan9" && bytes.Contains([]byte(e.Value), []byte{0}) {
+				base.Fatalf("go: internal error: encountered null byte in environment variable %s on non-plan9 platform", e.Name)
+			}
 			switch runtime.GOOS {
 			default:
-				fmt.Fprintf(w, "%s=\"%s\"\n", e.Name, e.Value)
+				fmt.Fprintf(w, "%s=%s\n", e.Name, shellQuote(e.Value))
 			case "plan9":
 				if strings.IndexByte(e.Value, '\x00') < 0 {
 					fmt.Fprintf(w, "%s='%s'\n", e.Name, strings.ReplaceAll(e.Value, "'", "''"))
@@ -426,17 +431,68 @@ func PrintEnv(w io.Writer, env []cfg.EnvVar) {
 						if x > 0 {
 							fmt.Fprintf(w, " ")
 						}
+						// TODO(#59979): Does this need to be quoted like above?
 						fmt.Fprintf(w, "%s", s)
 					}
 					fmt.Fprintf(w, ")\n")
 				}
 			case "windows":
-				fmt.Fprintf(w, "set %s=%s\n", e.Name, e.Value)
+				if hasNonGraphic(e.Value) {
+					base.Errorf("go: stripping unprintable or unescapable characters from %%%q%%", e.Name)
+				}
+				fmt.Fprintf(w, "set %s=%s\n", e.Name, batchEscape(e.Value))
 			}
 		}
 	}
 }
 
+func hasNonGraphic(s string) bool {
+	for _, c := range []byte(s) {
+		if c == '\r' || c == '\n' || (!unicode.IsGraphic(rune(c)) && !unicode.IsSpace(rune(c))) {
+			return true
+		}
+	}
+	return false
+}
+
+func shellQuote(s string) string {
+	var b bytes.Buffer
+	b.WriteByte('\'')
+	for _, x := range []byte(s) {
+		if x == '\'' {
+			// Close the single quoted string, add an escaped single quote,
+			// and start another single quoted string.
+			b.WriteString(`'\''`)
+		} else {
+			b.WriteByte(x)
+		}
+	}
+	b.WriteByte('\'')
+	return b.String()
+}
+
+func batchEscape(s string) string {
+	var b bytes.Buffer
+	for _, x := range []byte(s) {
+		if x == '\r' || x == '\n' || (!unicode.IsGraphic(rune(x)) && !unicode.IsSpace(rune(x))) {
+			b.WriteRune(unicode.ReplacementChar)
+			continue
+		}
+		switch x {
+		case '%':
+			b.WriteString("%%")
+		case '<', '>', '|', '&', '^':
+			// These are special characters that need to be escaped with ^. See
+			// https://learn.microsoft.com/en-us/windows-server/administration/windows-commands/set_1.
+			b.WriteByte('^')
+			b.WriteByte(x)
+		default:
+			b.WriteByte(x)
+		}
+	}
+	return b.String()
+}
+
 func printEnvAsJSON(env []cfg.EnvVar) {
 	m := make(map[string]string)
 	for _, e := range env {

src/cmd/go/internal/envcmd/env_test.go

@@ -0,0 +1,94 @@
+// Copyright 2022 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build unix || windows
+
+package envcmd
+
+import (
+	"bytes"
+	"cmd/go/internal/cfg"
+	"fmt"
+	"internal/testenv"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"runtime"
+	"testing"
+	"unicode"
+)
+
+func FuzzPrintEnvEscape(f *testing.F) {
+	f.Add(`$(echo 'cc"'; echo 'OOPS="oops')`)
+	f.Add("$(echo shell expansion 1>&2)")
+	f.Add("''")
+	f.Add(`C:\"Program Files"\`)
+	f.Add(`\\"Quoted Host"\\share`)
+	f.Add("\xfb")
+	f.Add("0")
+	f.Add("")
+	f.Add("''''''''")
+	f.Add("\r")
+	f.Add("\n")
+	f.Add("E,%")
+	f.Fuzz(func(t *testing.T, s string) {
+		t.Parallel()
+
+		for _, c := range []byte(s) {
+			if c == 0 {
+				t.Skipf("skipping %q: contains a null byte. Null bytes can't occur in the environment"+
+					" outside of Plan 9, which has different code path than Windows and Unix that this test"+
+					" isn't testing.", s)
+			}
+			if c > unicode.MaxASCII {
+				t.Skipf("skipping %#q: contains a non-ASCII character %q", s, c)
+			}
+			if !unicode.IsGraphic(rune(c)) && !unicode.IsSpace(rune(c)) {
+				t.Skipf("skipping %#q: contains non-graphic character %q", s, c)
+			}
+			if runtime.GOOS == "windows" && c == '\r' || c == '\n' {
+				t.Skipf("skipping %#q on Windows: contains unescapable character %q", s, c)
+			}
+		}
+
+		var b bytes.Buffer
+		if runtime.GOOS == "windows" {
+			b.WriteString("@echo off\n")
+		}
+		PrintEnv(&b, []cfg.EnvVar{{Name: "var", Value: s}})
+		var want string
+		if runtime.GOOS == "windows" {
+			fmt.Fprintf(&b, "echo \"%%var%%\"\n")
+			want += "\"" + s + "\"\r\n"
+		} else {
+			fmt.Fprintf(&b, "printf '%%s\\n' \"$var\"\n")
+			want += s + "\n"
+		}
+		scriptfilename := "script.sh"
+		if runtime.GOOS == "windows" {
+			scriptfilename = "script.bat"
+		}
+		scriptfile := filepath.Join(t.TempDir(), scriptfilename)
+		if err := os.WriteFile(scriptfile, b.Bytes(), 0777); err != nil {
+			t.Fatal(err)
+		}
+		t.Log(b.String())
+		var cmd *exec.Cmd
+		if runtime.GOOS == "windows" {
+			cmd = testenv.Command(t, "cmd.exe", "/C", scriptfile)
+		} else {
+			cmd = testenv.Command(t, "sh", "-c", scriptfile)
+		}
+		out, err := cmd.Output()
+		t.Log(string(out))
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		if string(out) != want {
+			t.Fatalf("output of running PrintEnv script and echoing variable: got: %q, want: %q",
+				string(out), want)
+		}
+	})
+}

src/cmd/go/testdata/script/env_sanitize.txt

@@ -0,0 +1,5 @@
+env GOFLAGS='$(echo ''cc"''; echo ''OOPS="oops'')'
+go env
+[GOOS:darwin] stdout 'GOFLAGS=''\$\(echo ''\\''''cc"''\\''''; echo ''\\''''OOPS="oops''\\''''\)'''
+[GOOS:linux] stdout 'GOFLAGS=''\$\(echo ''\\''''cc"''\\''''; echo ''\\''''OOPS="oops''\\''''\)'''
+[GOOS:windows] stdout 'set GOFLAGS=\$\(echo ''cc"''; echo ''OOPS="oops''\)'

src/cmd/go/testdata/script/work_env.txt

@@ -1,7 +1,7 @@
 go env GOWORK
 stdout '^'$GOPATH'[\\/]src[\\/]go.work$'
 go env
-stdout '^(set )?GOWORK="?'$GOPATH'[\\/]src[\\/]go.work"?$'
+stdout '^(set )?GOWORK=''?'$GOPATH'[\\/]src[\\/]go.work''?$'
 
 cd ..
 go env GOWORK