shim: user switcher process management struct

This change moves all user switcher and shim management to the shim package and withholds output while shim is alive. This also eliminated all exit scenarios where revert is skipped.

Signed-off-by: Ophestra Umiker <cat@ophivana.moe>

internal/shim/wayland.go

@@ -1,8 +1,12 @@
 package shim
 
 import (
+	"fmt"
 	"net"
 	"sync"
+	"syscall"
+
+	"git.ophivana.moe/security/fortify/internal/fmsg"
 )
 
 // Wayland implements wayland mediation.
@@ -11,7 +15,7 @@ type Wayland struct {
 	Path string
 
 	// wayland connection
-	*net.UnixConn
+	conn *net.UnixConn
 
 	connErr error
 	sync.Once
@@ -19,10 +23,46 @@ type Wayland struct {
 	done chan struct{}
 }
 
+func (wl *Wayland) WriteUnix(conn *net.UnixConn) error {
+	// connect to host wayland socket
+	if f, err := net.DialUnix("unix", nil, &net.UnixAddr{Name: wl.Path, Net: "unix"}); err != nil {
+		return fmsg.WrapErrorSuffix(err,
+			fmt.Sprintf("cannot connect to wayland at %q:", wl.Path))
+	} else {
+		fmsg.VPrintf("connected to wayland at %q", wl.Path)
+		wl.conn = f
+	}
+
+	// set up for passing wayland socket
+	if rc, err := wl.conn.SyscallConn(); err != nil {
+		return fmsg.WrapErrorSuffix(err, "cannot obtain raw wayland connection:")
+	} else {
+		ec := make(chan error)
+		go func() {
+			// pass wayland connection fd
+			if err = rc.Control(func(fd uintptr) {
+				if _, _, err = conn.WriteMsgUnix(nil, syscall.UnixRights(int(fd)), nil); err != nil {
+					ec <- fmsg.WrapErrorSuffix(err, "cannot pass wayland connection to shim:")
+					return
+				}
+				ec <- nil
+
+				// block until shim exits
+				<-wl.done
+				fmsg.VPrintln("releasing wayland connection")
+			}); err != nil {
+				ec <- fmsg.WrapErrorSuffix(err, "cannot obtain wayland connection fd:")
+				return
+			}
+		}()
+		return <-ec
+	}
+}
+
 func (wl *Wayland) Close() error {
 	wl.Do(func() {
 		close(wl.done)
-		wl.connErr = wl.UnixConn.Close()
+		wl.connErr = wl.conn.Close()
 	})
 
 	return wl.connErr