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// Package helper runs external helpers with optional sandboxing and manages their status/args pipes.
package helper
import (
"context"
"fmt"
"io"
"os"
"os/exec"
"slices"
"syscall"
"time"
"git.gensokyo.uk/security/fortify/helper/proc"
)
var (
WaitDelay = 2 * time.Second
)
const (
// FortifyHelper is set to 1 when args fd is enabled and 0 otherwise.
FortifyHelper = "FORTIFY_HELPER"
// FortifyStatus is set to 1 when stat fd is enabled and 0 otherwise.
FortifyStatus = "FORTIFY_STATUS"
)
type Helper interface {
// Stdin sets the standard input of Helper.
Stdin(r io.Reader) Helper
// Stdout sets the standard output of Helper.
Stdout(w io.Writer) Helper
// Stderr sets the standard error of Helper.
Stderr(w io.Writer) Helper
// SetEnv sets the environment of Helper.
SetEnv(env []string) Helper
// Start starts the helper process.
// A status pipe is passed to the helper if stat is true.
Start(ctx context.Context, stat bool) error
// Wait blocks until Helper exits and releases all its resources.
Wait() error
fmt.Stringer
}
func newHelperCmd(
h Helper, name string,
wt io.WriterTo, argF func(argsFd, statFd int) []string,
extraFiles []*os.File,
) (cmd *helperCmd) {
cmd = new(helperCmd)
cmd.r = h
cmd.name = name
cmd.extraFiles = new(proc.ExtraFilesPre)
for _, f := range extraFiles {
_, v := cmd.extraFiles.Append()
*v = f
}
argsFd := -1
if wt != nil {
f := proc.NewWriterTo(wt)
argsFd = int(proc.InitFile(f, cmd.extraFiles))
cmd.files = append(cmd.files, f)
cmd.hasArgsFd = true
}
cmd.argF = func(statFd int) []string { return argF(argsFd, statFd) }
return
}
// helperCmd wraps Cmd and implements methods shared across all Helper implementations.
type helperCmd struct {
// ref to parent
r Helper
// returns an array of arguments passed directly
// to the helper process
argF func(statFd int) []string
// whether argsFd is present
hasArgsFd bool
// closes statFd
stat io.Closer
// deferred extraFiles fulfillment
files []proc.File
// passed through to [proc.Fulfill] and [proc.InitFile]
extraFiles *proc.ExtraFilesPre
name string
stdin io.Reader
stdout, stderr io.Writer
env []string
*exec.Cmd
}
func (h *helperCmd) Stdin(r io.Reader) Helper { h.stdin = r; return h.r }
func (h *helperCmd) Stdout(w io.Writer) Helper { h.stdout = w; return h.r }
func (h *helperCmd) Stderr(w io.Writer) Helper { h.stderr = w; return h.r }
func (h *helperCmd) SetEnv(env []string) Helper { h.env = env; return h.r }
// finalise initialises the underlying [exec.Cmd] object.
func (h *helperCmd) finalise(ctx context.Context, stat bool) (args []string) {
h.Cmd = commandContext(ctx, h.name)
h.Cmd.Stdin, h.Cmd.Stdout, h.Cmd.Stderr = h.stdin, h.stdout, h.stderr
h.Cmd.Env = slices.Grow(h.env, 2)
if h.hasArgsFd {
h.Cmd.Env = append(h.Cmd.Env, FortifyHelper+"=1")
} else {
h.Cmd.Env = append(h.Cmd.Env, FortifyHelper+"=0")
}
h.Cmd.Cancel = func() error { return h.Cmd.Process.Signal(syscall.SIGTERM) }
h.Cmd.WaitDelay = WaitDelay
statFd := -1
if stat {
f := proc.NewStat(&h.stat)
statFd = int(proc.InitFile(f, h.extraFiles))
h.files = append(h.files, f)
h.Cmd.Env = append(h.Cmd.Env, FortifyStatus+"=1")
// stat is populated on fulfill
h.Cmd.Cancel = func() error { return h.stat.Close() }
} else {
h.Cmd.Env = append(h.Cmd.Env, FortifyStatus+"=0")
}
return h.argF(statFd)
}
var commandContext = exec.CommandContext
|
