devices: vhost-user: fs: keep executor fd inside jail

A previous commit moved the creation of the executor for the vhost-user
device processes before the minijail jail_and_fork() call, and the file
descriptor of the executor was not marked for preservation when entering
the jail, so running the vhost-user-fs device would result in errors
like this:

  [WARNING:cros_async/src/sys/unix/uring_executor.rs:343] Failed to
  submit NOP for waking up executor: Failed to enter io uring: 9

This is because the io_uring context file descriptor was no longer
valid, so uring system calls would return 9 (EBADF).

Add AsRawDescriptors implementations to UringExecutor and FdExecutor so
we can preserve the fd across the minijail fork.

Other vhost-user devices were not affected because they don't enter a
jail; the fs device requires this so it can do uid/gid remapping.

BUG=b:231396155
TEST=crosvm device fs --socket /tmp/vhost.sock --tag test --shared-dir /

Fixes: d368c1520a ("devices: vhost-user: fs: remove global executor variable")
Change-Id: I38cf02034bbc28de2582e2ea92bdc13b1d6055d2
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosvm/+/3628292
Reviewed-by: Keiichi Watanabe <keiichiw@chromium.org>
Tested-by: kokoro <noreply+kokoro@google.com>
Commit-Queue: Lepton Wu <lepton@chromium.org>

cros_async/src/sys/unix/executor.rs

@@ -6,6 +6,8 @@ use std::future::Future;
 
 use async_task::Task;
 
+use base::{AsRawDescriptors, RawDescriptor};
+
 use super::{
     poll_source::Error as PollError, uring_executor::use_uring, FdExecutor, PollSource,
     URingExecutor, UringSource,
@@ -352,3 +354,12 @@ impl Executor {
         }
     }
 }
+
+impl AsRawDescriptors for Executor {
+    fn as_raw_descriptors(&self) -> Vec<RawDescriptor> {
+        match self {
+            Executor::Uring(ex) => ex.as_raw_descriptors(),
+            Executor::Fd(ex) => ex.as_raw_descriptors(),
+        }
+    }
+}

cros_async/src/sys/unix/fd_executor.rs

@@ -23,7 +23,10 @@ use std::{
 };
 
 use async_task::Task;
-use base::{add_fd_flags, warn, AsRawDescriptor, EpollContext, EpollEvents, Event, WatchingEvents};
+use base::{
+    add_fd_flags, warn, AsRawDescriptor, AsRawDescriptors, EpollContext, EpollEvents, Event,
+    RawDescriptor, WatchingEvents,
+};
 use futures::task::noop_waker;
 use pin_utils::pin_mut;
 use remain::sorted;
@@ -271,10 +274,17 @@ struct RawExecutor {
     blocking_pool: BlockingPool,
     state: AtomicI32,
     notify: Event,
+    // Descriptor of the original event that was cloned to create notify.
+    // This is only needed for the AsRawDescriptors implementation.
+    notify_dup: RawDescriptor,
 }
 
 impl RawExecutor {
-    fn new(notify: Event) -> Result<Self> {
+    fn new(notify: &Event) -> Result<Self> {
+        // Save the original descriptor before cloning. This descriptor will be used when creating
+        // the notify task, so we need to preserve it for AsRawDescriptors.
+        let notify_dup = notify.as_raw_descriptor();
+        let notify = notify.try_clone().map_err(Error::CloneEvent)?;
         Ok(RawExecutor {
             queue: RunnableQueue::new(),
             poll_ctx: EpollContext::new().map_err(Error::CreatingContext)?,
@@ -282,6 +292,7 @@ impl RawExecutor {
             blocking_pool: Default::default(),
             state: AtomicI32::new(PROCESSING),
             notify,
+            notify_dup,
         })
     }
 
@@ -445,6 +456,16 @@ impl RawExecutor {
     }
 }
 
+impl AsRawDescriptors for RawExecutor {
+    fn as_raw_descriptors(&self) -> Vec<RawDescriptor> {
+        vec![
+            self.poll_ctx.as_raw_descriptor(),
+            self.notify.as_raw_descriptor(),
+            self.notify_dup,
+        ]
+    }
+}
+
 impl WeakWake for RawExecutor {
     fn wake_by_ref(weak_self: &Weak<Self>) {
         if let Some(arc_self) = weak_self.upgrade() {
@@ -494,11 +515,7 @@ pub struct FdExecutor {
 impl FdExecutor {
     pub fn new() -> Result<FdExecutor> {
         let notify = Event::new().map_err(Error::CreateEvent)?;
-        let raw = notify
-            .try_clone()
-            .map_err(Error::CloneEvent)
-            .and_then(RawExecutor::new)
-            .map(Arc::new)?;
+        let raw = RawExecutor::new(&notify).map(Arc::new)?;
 
         raw.spawn(notify_task(notify, Arc::downgrade(&raw)))
             .detach();
@@ -553,6 +570,12 @@ impl FdExecutor {
     }
 }
 
+impl AsRawDescriptors for FdExecutor {
+    fn as_raw_descriptors(&self) -> Vec<RawDescriptor> {
+        self.raw.as_raw_descriptors()
+    }
+}
+
 // Used to `dup` the FDs passed to the executor so there is a guarantee they aren't closed while
 // waiting in TLS to be added to the main polling context.
 unsafe fn dup_fd(fd: RawFd) -> Result<RawFd> {

cros_async/src/sys/unix/uring_executor.rs

@@ -73,7 +73,7 @@ use std::{
 };
 
 use async_task::Task;
-use base::{warn, AsRawDescriptor, WatchingEvents};
+use base::{warn, AsRawDescriptor, RawDescriptor, WatchingEvents};
 use futures::task::noop_waker;
 use io_uring::URingContext;
 use once_cell::sync::Lazy;
@@ -726,6 +726,12 @@ impl RawExecutor {
     }
 }
 
+impl AsRawDescriptor for RawExecutor {
+    fn as_raw_descriptor(&self) -> RawDescriptor {
+        self.ctx.as_raw_descriptor()
+    }
+}
+
 impl WeakWake for RawExecutor {
     fn wake_by_ref(weak_self: &Weak<Self>) {
         if let Some(arc_self) = weak_self.upgrade() {
@@ -850,6 +856,12 @@ impl URingExecutor {
     }
 }
 
+impl AsRawDescriptor for URingExecutor {
+    fn as_raw_descriptor(&self) -> RawDescriptor {
+        self.raw.as_raw_descriptor()
+    }
+}
+
 // Used to dup the FDs passed to the executor so there is a guarantee they aren't closed while
 // waiting in TLS to be added to the main polling context.
 unsafe fn dup_fd(fd: RawFd) -> Result<RawFd> {

devices/src/virtio/vhost/user/device/fs.rs

@@ -10,7 +10,10 @@ use std::sync::Arc;
 
 use anyhow::{anyhow, bail, Context};
 use argh::FromArgs;
-use base::{error, get_max_open_files, warn, Event, RawDescriptor, Tube, UnlinkUnixListener};
+use base::{
+    error, get_max_open_files, warn, AsRawDescriptors, Event, RawDescriptor, Tube,
+    UnlinkUnixListener,
+};
 use cros_async::{EventAsync, Executor};
 use data_model::{DataInit, Le32};
 use fuse::Server;
@@ -142,10 +145,13 @@ impl FsBackend {
         let mut keep_rds: Vec<RawDescriptor> = [0, 1, 2].to_vec();
         keep_rds.append(&mut fs.keep_rds());
 
+        let ex = ex.clone();
+        keep_rds.extend(ex.as_raw_descriptors());
+
         let server = Arc::new(Server::new(fs));
 
         Ok(FsBackend {
-            ex: ex.clone(),
+            ex,
             server,
             tag: fs_tag,
             avail_features,