helper/bwrap: ordered filesystem args

The argument builder was written based on the incorrect assumption that bwrap arguments are unordered. The argument builder is replaced in this commit to correct that mistake.

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

internal/app/system.go

@@ -59,6 +59,7 @@ type appSeal struct {
 // appSealTx contains the system-level component of the app seal
 type appSealTx struct {
 	bwrap *bwrap.Config
+	tmpfs []string
 
 	// reference to D-Bus proxy instance, nil if disabled
 	dbus *dbus.Proxy
@@ -110,15 +111,6 @@ func (tx *appSealTx) setEnv(k, v string) {
 	tx.bwrap.SetEnv[k] = v
 }
 
-// bind mounts a directory within the sandbox
-func (tx *appSealTx) bind(src, dest string, ro bool) {
-	if !ro {
-		tx.bwrap.Bind = append(tx.bwrap.Bind, [2]string{src, dest})
-	} else {
-		tx.bwrap.ROBind = append(tx.bwrap.ROBind, [2]string{src, dest})
-	}
-}
-
 // ensure appends a directory ensure action
 func (tx *appSealTx) ensure(path string, perm os.FileMode) {
 	tx.mkdir = append(tx.mkdir, appEnsureEntry{path, perm, false})
@@ -183,14 +175,14 @@ func (tx *appSealTx) changeHosts(username string) {
 func (tx *appSealTx) writeFile(dst string, data []byte) {
 	tx.files = append(tx.files, [2]string{dst, string(data)})
 	tx.updatePerm(dst, acl.Read)
-	tx.bind(dst, dst, true)
+	tx.bwrap.Bind(dst, dst)
 }
 
 // copyFile appends a tmpfiles action
 func (tx *appSealTx) copyFile(dst, src string) {
 	tx.tmpfiles = append(tx.tmpfiles, [2]string{dst, src})
 	tx.updatePerm(dst, acl.Read)
-	tx.bind(dst, dst, true)
+	tx.bwrap.Bind(dst, dst)
 }
 
 // link appends a hardlink action
@@ -324,6 +316,12 @@ func (tx *appSealTx) commit() error {
 
 	// disarm partial commit rollback
 	txp = nil
+
+	// queue tmpfs at the end of tx.bwrap.Filesystem
+	for _, dest := range tx.tmpfs {
+		tx.bwrap.Tmpfs(dest, 8*1024)
+	}
+
 	return nil
 }
 
@@ -416,10 +414,10 @@ func (seal *appSeal) shareAll(bus [2]*dbus.Config) error {
 	}
 	seal.shared = true
 
+	targetTmpdir := seal.shareTmpdirChild()
+	verbose.Printf("child tmpdir %q configured\n", targetTmpdir)
 	seal.shareRuntime()
 	seal.shareSystem()
-	targetRuntime := seal.shareRuntimeChild()
-	verbose.Printf("child runtime data dir '%s' configured\n", targetRuntime)
 	if err := seal.shareDisplay(); err != nil {
 		return err
 	}