fix: register external fds with userspace FILETABLE

Socket and RawEventQueue create fds via libredox raw syscalls that
bypass the redox-rt userspace FILETABLE. FdGuard::dup then reserves
these positions, causing SYS_DUP_INTO to destroy the existing fds.

bootstrap/src/exec.rs

@@ -253,9 +253,14 @@ pub fn main() -> ! {
         &extrainfo,
         None,
     )
-    .ok()
+    .unwrap_or_else(|e| {
-    .flatten()
+        let step = unsafe { redox_rt::proc::FEXEC_STEP };
-    .expect("failed to execute init");
+        panic!("fexec_impl error: {:?} at step {}", e, step);
+    })
+    .unwrap_or_else(|| panic!("fexec_impl returned None (no interpreter)"))
+    else {
+        panic!("fexec_impl returned unexpected variant");
+    };
 
     // According to elf(5), PT_INTERP requires that the interpreter path be
     // null-terminated. Violating this should therefore give the "format error" ENOEXEC.

bootstrap/src/initfs.rs

@@ -123,7 +123,7 @@ impl SchemeSync for InitFsScheme {
     ) -> Result<OpenResult> {
         if !matches!(
             self.handles.get(&dirfd).ok_or(Error::new(EBADF))?,
-            Handle::SchemeRoot
+            Handle::SchemeRoot | Handle::Node(_)
         ) {
             return Err(Error::new(EACCES));
         }

bootstrap/src/procmgr.rs

@@ -49,7 +49,12 @@ pub fn run(write_fd: FdGuard, socket: Socket, auth: FdGuard, event: FdGuard) ->
     // TODO?
     let socket_ident = socket.inner().raw();
 
+    redox_rt::proc::register_external_fd(socket.inner().raw())
+        .expect("failed to register socket fd with userspace filetable");
+
     let queue = RawEventQueue::new(event.as_raw_fd()).expect("failed to create event queue");
+    redox_rt::proc::register_external_fd(queue.0.as_raw_fd())
+        .expect("failed to register event queue fd with userspace filetable");
     drop(event);
 
     queue