internal: move shim and init into app

This structure makes more sense, as both processes are part of an app's lifecycle.

Signed-off-by: Ophestra <cat@gensokyo.uk>

1 files changed, 139 insertions, 0 deletions

diff --git a/internal/app/shim/manager.go b/internal/app/shim/manager.go
new file mode 100644
index 00000000..106e4865
--- /dev/null
+++ b/internal/app/shim/manager.go
@@ -0,0 +1,139 @@
+package shim
+
+import (
+	"context"
+	"encoding/gob"
+	"errors"
+	"os"
+	"os/exec"
+	"strconv"
+	"strings"
+	"time"
+
+	"git.gensokyo.uk/security/fortify/helper/proc"
+	"git.gensokyo.uk/security/fortify/internal"
+	"git.gensokyo.uk/security/fortify/internal/fmsg"
+)
+
+// used by the parent process
+
+type Shim struct {
+	// user switcher process
+	cmd *exec.Cmd
+	// fallback exit notifier with error returned killing the process
+	killFallback chan error
+	// monitor to shim encoder
+	encoder *gob.Encoder
+	// bwrap --sync-fd value
+	sync *uintptr
+}
+
+func (s *Shim) String() string {
+	if s.cmd == nil {
+		return "(unused shim manager)"
+	}
+	return s.cmd.String()
+}
+
+func (s *Shim) Unwrap() *exec.Cmd {
+	return s.cmd
+}
+
+func (s *Shim) WaitFallback() chan error {
+	return s.killFallback
+}
+
+func (s *Shim) Start(
+	// string representation of application id
+	aid string,
+	// string representation of supplementary group ids
+	supp []string,
+	// bwrap --sync-fd
+	syncFd *os.File,
+) (*time.Time, error) {
+	// prepare user switcher invocation
+	var fsu string
+	if p, ok := internal.Path(internal.Fsu); !ok {
+		fmsg.Fatal("invalid fsu path, this copy of fortify is not compiled correctly")
+		panic("unreachable")
+	} else {
+		fsu = p
+	}
+	s.cmd = exec.Command(fsu)
+
+	// pass shim setup pipe
+	if fd, e, err := proc.Setup(&s.cmd.ExtraFiles); err != nil {
+		return nil, fmsg.WrapErrorSuffix(err,
+			"cannot create shim setup pipe:")
+	} else {
+		s.encoder = e
+		s.cmd.Env = []string{
+			Env + "=" + strconv.Itoa(fd),
+			"FORTIFY_APP_ID=" + aid,
+		}
+	}
+
+	// format fsu supplementary groups
+	if len(supp) > 0 {
+		fmsg.VPrintf("attaching supplementary group ids %s", supp)
+		s.cmd.Env = append(s.cmd.Env, "FORTIFY_GROUPS="+strings.Join(supp, " "))
+	}
+	s.cmd.Stdin, s.cmd.Stdout, s.cmd.Stderr = os.Stdin, os.Stdout, os.Stderr
+	s.cmd.Dir = "/"
+
+	// pass sync fd if set
+	if syncFd != nil {
+		fd := proc.ExtraFile(s.cmd, syncFd)
+		s.sync = &fd
+	}
+
+	fmsg.VPrintln("starting shim via fsu:", s.cmd)
+	// withhold messages to stderr
+	fmsg.Suspend()
+	if err := s.cmd.Start(); err != nil {
+		return nil, fmsg.WrapErrorSuffix(err,
+			"cannot start fsu:")
+	}
+	startTime := time.Now().UTC()
+	return &startTime, nil
+}
+
+func (s *Shim) Serve(ctx context.Context, payload *Payload) error {
+	// kill shim if something goes wrong and an error is returned
+	s.killFallback = make(chan error, 1)
+	killShim := func() {
+		if err := s.cmd.Process.Signal(os.Interrupt); err != nil {
+			s.killFallback <- err
+		}
+	}
+	defer func() { killShim() }()
+
+	payload.Sync = s.sync
+	encodeErr := make(chan error)
+	go func() { encodeErr <- s.encoder.Encode(payload) }()
+
+	select {
+	// encode return indicates setup completion
+	case err := <-encodeErr:
+		if err != nil {
+			return fmsg.WrapErrorSuffix(err,
+				"cannot transmit shim config:")
+		}
+		killShim = func() {}
+		return nil
+
+	// setup canceled before payload was accepted
+	case <-ctx.Done():
+		err := ctx.Err()
+		if errors.Is(err, context.Canceled) {
+			return fmsg.WrapError(errors.New("shim setup canceled"),
+				"shim setup canceled")
+		}
+		if errors.Is(err, context.DeadlineExceeded) {
+			return fmsg.WrapError(errors.New("deadline exceeded waiting for shim"),
+				"deadline exceeded waiting for shim")
+		}
+		// unreachable
+		return err
+	}
+}