Roland Shoemaker | b64e53b | 2021-01-11 10:06:18 -0800 | [diff] [blame] | 1 | // Copyright 2020 The Go Authors. All rights reserved. |
| 2 | // Use of this source code is governed by a BSD-style |
| 3 | // license that can be found in the LICENSE file. |
| 4 | |
| 5 | // Package execabs is a drop-in replacement for os/exec |
| 6 | // that requires PATH lookups to find absolute paths. |
| 7 | // That is, execabs.Command("cmd") runs the same PATH lookup |
| 8 | // as exec.Command("cmd"), but if the result is a path |
| 9 | // which is relative, the Run and Start methods will report |
| 10 | // an error instead of running the executable. |
| 11 | // |
| 12 | // See https://blog.golang.org/path-security for more information |
| 13 | // about when it may be necessary or appropriate to use this package. |
| 14 | package execabs |
| 15 | |
| 16 | import ( |
| 17 | "context" |
| 18 | "fmt" |
| 19 | "os/exec" |
| 20 | "path/filepath" |
| 21 | "reflect" |
| 22 | "unsafe" |
| 23 | ) |
| 24 | |
| 25 | // ErrNotFound is the error resulting if a path search failed to find an executable file. |
| 26 | // It is an alias for exec.ErrNotFound. |
| 27 | var ErrNotFound = exec.ErrNotFound |
| 28 | |
| 29 | // Cmd represents an external command being prepared or run. |
| 30 | // It is an alias for exec.Cmd. |
| 31 | type Cmd = exec.Cmd |
| 32 | |
| 33 | // Error is returned by LookPath when it fails to classify a file as an executable. |
| 34 | // It is an alias for exec.Error. |
| 35 | type Error = exec.Error |
| 36 | |
| 37 | // An ExitError reports an unsuccessful exit by a command. |
| 38 | // It is an alias for exec.ExitError. |
| 39 | type ExitError = exec.ExitError |
| 40 | |
| 41 | func relError(file, path string) error { |
| 42 | return fmt.Errorf("%s resolves to executable in current directory (.%c%s)", file, filepath.Separator, path) |
| 43 | } |
| 44 | |
| 45 | // LookPath searches for an executable named file in the directories |
| 46 | // named by the PATH environment variable. If file contains a slash, |
| 47 | // it is tried directly and the PATH is not consulted. The result will be |
| 48 | // an absolute path. |
| 49 | // |
| 50 | // LookPath differs from exec.LookPath in its handling of PATH lookups, |
| 51 | // which are used for file names without slashes. If exec.LookPath's |
| 52 | // PATH lookup would have returned an executable from the current directory, |
| 53 | // LookPath instead returns an error. |
| 54 | func LookPath(file string) (string, error) { |
| 55 | path, err := exec.LookPath(file) |
Russ Cox | b6088cc | 2022-04-29 20:33:09 -0400 | [diff] [blame] | 56 | if err != nil && !isGo119ErrDot(err) { |
Roland Shoemaker | b64e53b | 2021-01-11 10:06:18 -0800 | [diff] [blame] | 57 | return "", err |
| 58 | } |
| 59 | if filepath.Base(file) == file && !filepath.IsAbs(path) { |
| 60 | return "", relError(file, path) |
| 61 | } |
| 62 | return path, nil |
| 63 | } |
| 64 | |
| 65 | func fixCmd(name string, cmd *exec.Cmd) { |
| 66 | if filepath.Base(name) == name && !filepath.IsAbs(cmd.Path) { |
| 67 | // exec.Command was called with a bare binary name and |
| 68 | // exec.LookPath returned a path which is not absolute. |
| 69 | // Set cmd.lookPathErr and clear cmd.Path so that it |
| 70 | // cannot be run. |
| 71 | lookPathErr := (*error)(unsafe.Pointer(reflect.ValueOf(cmd).Elem().FieldByName("lookPathErr").Addr().Pointer())) |
| 72 | if *lookPathErr == nil { |
| 73 | *lookPathErr = relError(name, cmd.Path) |
| 74 | } |
| 75 | cmd.Path = "" |
| 76 | } |
| 77 | } |
| 78 | |
| 79 | // CommandContext is like Command but includes a context. |
| 80 | // |
| 81 | // The provided context is used to kill the process (by calling os.Process.Kill) |
| 82 | // if the context becomes done before the command completes on its own. |
| 83 | func CommandContext(ctx context.Context, name string, arg ...string) *exec.Cmd { |
| 84 | cmd := exec.CommandContext(ctx, name, arg...) |
| 85 | fixCmd(name, cmd) |
| 86 | return cmd |
| 87 | |
| 88 | } |
| 89 | |
| 90 | // Command returns the Cmd struct to execute the named program with the given arguments. |
| 91 | // See exec.Command for most details. |
| 92 | // |
| 93 | // Command differs from exec.Command in its handling of PATH lookups, |
| 94 | // which are used when the program name contains no slashes. |
| 95 | // If exec.Command would have returned an exec.Cmd configured to run an |
| 96 | // executable from the current directory, Command instead |
| 97 | // returns an exec.Cmd that will return an error from Start or Run. |
| 98 | func Command(name string, arg ...string) *exec.Cmd { |
| 99 | cmd := exec.Command(name, arg...) |
| 100 | fixCmd(name, cmd) |
| 101 | return cmd |
| 102 | } |