os/exec: return error when PATH lookup would use current directory

Following discussion on #43724, change os/exec to take the
approach of golang.org/x/sys/execabs, refusing to respect
path entries mentioning relative paths by default.

Code that insists on being able to find executables in relative
directories in the path will need to add a couple lines to override the error.

See the updated package docs in exec.go for more details.

Fixes #43724.
Fixes #43947.

Change-Id: I73c1214f322b60b4167a23e956e933d50470fe13
Reviewed-on: https://go-review.googlesource.com/c/go/+/381374
Reviewed-by: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Bryan Mills <bcmills@google.com>

2 files changed, 3 insertions, 140 deletions

diff --git a/src/internal/execabs/execabs.go b/src/internal/execabs/execabs.go
index 9a05d971da..5f60fbb119 100644
--- a/src/internal/execabs/execabs.go
+++ b/src/internal/execabs/execabs.go
@@ -12,11 +12,7 @@ package execabs
 
 import (
 	"context"
-	"fmt"
 	"os/exec"
-	"path/filepath"
-	"reflect"
-	"unsafe"
 )
 
 var ErrNotFound = exec.ErrNotFound
@@ -27,44 +23,14 @@ type (
 	ExitError = exec.ExitError
 )
 
-func relError(file, path string) error {
-	return fmt.Errorf("%s resolves to executable relative to current directory (.%c%s)", file, filepath.Separator, path)
-}
-
 func LookPath(file string) (string, error) {
-	path, err := exec.LookPath(file)
-	if err != nil {
-		return "", err
-	}
-	if filepath.Base(file) == file && !filepath.IsAbs(path) {
-		return "", relError(file, path)
-	}
-	return path, nil
-}
-
-func fixCmd(name string, cmd *exec.Cmd) {
-	if filepath.Base(name) == name && !filepath.IsAbs(cmd.Path) {
-		// exec.Command was called with a bare binary name and
-		// exec.LookPath returned a path which is not absolute.
-		// Set cmd.lookPathErr and clear cmd.Path so that it
-		// cannot be run.
-		lookPathErr := (*error)(unsafe.Pointer(reflect.ValueOf(cmd).Elem().FieldByName("lookPathErr").Addr().Pointer()))
-		if *lookPathErr == nil {
-			*lookPathErr = relError(name, cmd.Path)
-		}
-		cmd.Path = ""
-	}
+	return exec.LookPath(file)
 }
 
 func CommandContext(ctx context.Context, name string, arg ...string) *exec.Cmd {
-	cmd := exec.CommandContext(ctx, name, arg...)
-	fixCmd(name, cmd)
-	return cmd
-
+	return exec.CommandContext(ctx, name, arg...)
 }
 
 func Command(name string, arg ...string) *exec.Cmd {
-	cmd := exec.Command(name, arg...)
-	fixCmd(name, cmd)
-	return cmd
+	return exec.Command(name, arg...)
 }
diff --git a/src/internal/execabs/execabs_test.go b/src/internal/execabs/execabs_test.go
deleted file mode 100644
index 97a3f39b4a..0000000000
--- a/src/internal/execabs/execabs_test.go
+++ /dev/null
@@ -1,103 +0,0 @@
-// Copyright 2020 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.
-
-package execabs
-
-import (
-	"context"
-	"fmt"
-	"internal/testenv"
-	"os"
-	"os/exec"
-	"path/filepath"
-	"runtime"
-	"testing"
-)
-
-func TestFixCmd(t *testing.T) {
-	cmd := &exec.Cmd{Path: "hello"}
-	fixCmd("hello", cmd)
-	if cmd.Path != "" {
-		t.Error("fixCmd didn't clear cmd.Path")
-	}
-	expectedErr := fmt.Sprintf("hello resolves to executable relative to current directory (.%chello)", filepath.Separator)
-	if err := cmd.Run(); err == nil {
-		t.Fatal("Command.Run didn't fail")
-	} else if err.Error() != expectedErr {
-		t.Fatalf("Command.Run returned unexpected error: want %q, got %q", expectedErr, err.Error())
-	}
-}
-
-func TestCommand(t *testing.T) {
-	testenv.MustHaveExec(t)
-
-	for _, cmd := range []func(string) *Cmd{
-		func(s string) *Cmd { return Command(s) },
-		func(s string) *Cmd { return CommandContext(context.Background(), s) },
-	} {
-		tmpDir := t.TempDir()
-		executable := "execabs-test"
-		if runtime.GOOS == "windows" {
-			executable += ".exe"
-		}
-		if err := os.WriteFile(filepath.Join(tmpDir, executable), []byte{1, 2, 3}, 0111); err != nil {
-			t.Fatalf("os.WriteFile failed: %s", err)
-		}
-		cwd, err := os.Getwd()
-		if err != nil {
-			t.Fatalf("os.Getwd failed: %s", err)
-		}
-		defer os.Chdir(cwd)
-		if err = os.Chdir(tmpDir); err != nil {
-			t.Fatalf("os.Chdir failed: %s", err)
-		}
-		if runtime.GOOS != "windows" {
-			// add "." to PATH so that exec.LookPath looks in the current directory on
-			// non-windows platforms as well
-			origPath := os.Getenv("PATH")
-			defer os.Setenv("PATH", origPath)
-			os.Setenv("PATH", fmt.Sprintf(".:%s", origPath))
-		}
-		expectedErr := fmt.Sprintf("execabs-test resolves to executable relative to current directory (.%c%s)", filepath.Separator, executable)
-		if err = cmd("execabs-test").Run(); err == nil {
-			t.Fatalf("Command.Run didn't fail when exec.LookPath returned a relative path")
-		} else if err.Error() != expectedErr {
-			t.Errorf("Command.Run returned unexpected error: want %q, got %q", expectedErr, err.Error())
-		}
-	}
-}
-
-func TestLookPath(t *testing.T) {
-	testenv.MustHaveExec(t)
-
-	tmpDir := t.TempDir()
-	executable := "execabs-test"
-	if runtime.GOOS == "windows" {
-		executable += ".exe"
-	}
-	if err := os.WriteFile(filepath.Join(tmpDir, executable), []byte{1, 2, 3}, 0111); err != nil {
-		t.Fatalf("os.WriteFile failed: %s", err)
-	}
-	cwd, err := os.Getwd()
-	if err != nil {
-		t.Fatalf("os.Getwd failed: %s", err)
-	}
-	defer os.Chdir(cwd)
-	if err = os.Chdir(tmpDir); err != nil {
-		t.Fatalf("os.Chdir failed: %s", err)
-	}
-	if runtime.GOOS != "windows" {
-		// add "." to PATH so that exec.LookPath looks in the current directory on
-		// non-windows platforms as well
-		origPath := os.Getenv("PATH")
-		defer os.Setenv("PATH", origPath)
-		os.Setenv("PATH", fmt.Sprintf(".:%s", origPath))
-	}
-	expectedErr := fmt.Sprintf("execabs-test resolves to executable relative to current directory (.%c%s)", filepath.Separator, executable)
-	if _, err := LookPath("execabs-test"); err == nil {
-		t.Fatalf("LookPath didn't fail when finding a non-relative path")
-	} else if err.Error() != expectedErr {
-		t.Errorf("LookPath returned unexpected error: want %q, got %q", expectedErr, err.Error())
-	}
-}