app: support mapping target uid as privileged uid in sandbox

Chromium's D-Bus client implementation refuses to work when its getuid call returns a different value than what the D-Bus server is running as. The reason behind this is not fully understood, but this workaround is implemented to support chromium and electron apps. This is not used by default since it has many side effects that break many other programs, like SSH on NixOS.

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

internal/app/system.go

@@ -20,6 +20,11 @@ type appSealSys struct {
 	// target user sealed from config
 	user *user.User
 
+	// mapped uid and gid in user namespace
+	mappedID int
+	// string representation of mappedID
+	mappedIDString string
+
 	needRevert bool
 	saveState  bool
 	*system.I