Don't eat error from epoll_ctl EPOLL_CTL_ADD

Docker maps stdin to `/dev/null` which doesn't support epoll. Host FD
was ignoring the error and suceeding the epoll_ctl call from the
container, giving false impressing that epoll would be notified.

This required plumbing failure to all waiter.Waitable.EventRegister
callers and implementers.

Closes #6795

PiperOrigin-RevId: 414797621

images/basic/integrationtest/host_fd.c

@@ -13,17 +13,44 @@
 // limitations under the License.
 
 #include <err.h>
+#include <errno.h>
+#include <sys/epoll.h>
 #include <sys/ioctl.h>
 #include <unistd.h>
 
 // Tests that FIONREAD is supported with host FD.
-int main(int argc, char** argv) {
+void testFionread() {
   int size = 0;
   if (ioctl(STDOUT_FILENO, FIONREAD, &size) < 0) {
     err(1, "ioctl(stdin, FIONREAD)");
   }
   if (size != 0) {
     err(1, "FIONREAD wrong size, want: 0, got: %d", size);
   }
+}
+
+// Docker maps stdin to /dev/null which doesn't support epoll. Check that error
+// is correctly propagated.
+void testEpoll() {
+  int fd = epoll_create(1);
+  if (fd < 0) {
+    err(1, "epoll_create");
+  }
+
+  struct epoll_event event;
+  event.events = EPOLLIN;
+  event.data.u64 = 123;
+  int res = epoll_ctl(fd, EPOLL_CTL_ADD, 0, &event);
+  if (res != -1) {
+    err(1, "epoll_ctl(EPOLL_CTL_ADD, stdin) should have failed");
+  }
+  if (errno != EPERM) {
+    err(1, "epoll_ctl(EPOLL_CTL_ADD, stdin) should have returned EPERM");
+  }
+}
+
+int main(int argc, char** argv) {
+  testFionread();
+  testEpoll();
   return 0;
 }

pkg/sentry/devices/tundev/tundev.go

@@ -152,8 +152,9 @@ func (fd *tunFD) Readiness(mask waiter.EventMask) waiter.EventMask {
 }
 
 // EventRegister implements watier.Waitable.EventRegister.
-func (fd *tunFD) EventRegister(e *waiter.Entry) {
+func (fd *tunFD) EventRegister(e *waiter.Entry) error {
 	fd.device.EventRegister(e)
+	return nil
 }
 
 // EventUnregister implements watier.Waitable.EventUnregister.

pkg/sentry/fs/dev/net_tun.go

@@ -158,8 +158,9 @@ func (n *netTunFileOperations) Readiness(mask waiter.EventMask) waiter.EventMask
 }
 
 // EventRegister implements watier.Waitable.EventRegister.
-func (n *netTunFileOperations) EventRegister(e *waiter.Entry) {
+func (n *netTunFileOperations) EventRegister(e *waiter.Entry) error {
 	n.device.EventRegister(e)
+	return nil
 }
 
 // EventUnregister implements watier.Waitable.EventUnregister.

pkg/sentry/fs/fdpipe/pipe.go

@@ -16,6 +16,7 @@
 package fdpipe
 
 import (
+	"fmt"
 	"os"
 
 	"golang.org/x/sys/unix"
@@ -99,15 +100,21 @@ func (p *pipeOperations) init() error {
 }
 
 // EventRegister implements waiter.Waitable.EventRegister.
-func (p *pipeOperations) EventRegister(e *waiter.Entry) {
+func (p *pipeOperations) EventRegister(e *waiter.Entry) error {
 	p.Queue.EventRegister(e)
-	fdnotifier.UpdateFD(int32(p.file.FD()))
+	if err := fdnotifier.UpdateFD(int32(p.file.FD())); err != nil {
+		p.Queue.EventUnregister(e)
+		return err
+	}
+	return nil
 }
 
 // EventUnregister implements waiter.Waitable.EventUnregister.
 func (p *pipeOperations) EventUnregister(e *waiter.Entry) {
 	p.Queue.EventUnregister(e)
-	fdnotifier.UpdateFD(int32(p.file.FD()))
+	if err := fdnotifier.UpdateFD(int32(p.file.FD())); err != nil {
+		panic(fmt.Sprint("UpdateFD:", err))
+	}
 }
 
 // Readiness returns a mask of ready events for stream.

pkg/sentry/fs/file.go

@@ -159,7 +159,8 @@ func (f *File) SetFlags(newFlags SettableFileFlags) {
 	f.flags.Append = newFlags.Append
 	if f.async != nil {
 		if newFlags.Async && !f.flags.Async {
-			f.async.Register(f)
+			// Ignore error given that VFS1 will not be here much longer.
+			_ = f.async.Register(f)
 		}
 		if !newFlags.Async && f.flags.Async {
 			f.async.Unregister(f)
@@ -180,8 +181,8 @@ func (f *File) Readiness(mask waiter.EventMask) waiter.EventMask {
 }
 
 // EventRegister implements waiter.Waitable.EventRegister.
-func (f *File) EventRegister(e *waiter.Entry) {
-	f.FileOperations.EventRegister(e)
+func (f *File) EventRegister(e *waiter.Entry) error {
+	return f.FileOperations.EventRegister(e)
 }
 
 // EventUnregister implements waiter.Waitable.EventUnregister.
@@ -424,23 +425,25 @@ func (f *File) Msync(ctx context.Context, mr memmap.MappableRange) error {
 
 // A FileAsync sends signals to its owner when w is ready for IO.
 type FileAsync interface {
-	Register(w waiter.Waitable)
+	Register(w waiter.Waitable) error
 	Unregister(w waiter.Waitable)
 }
 
 // Async gets the stored FileAsync or creates a new one with the supplied
 // function. If the supplied function is nil, no FileAsync is created and the
 // current value is returned.
-func (f *File) Async(newAsync func() FileAsync) FileAsync {
+func (f *File) Async(newAsync func() FileAsync) (FileAsync, error) {
 	f.flagsMu.Lock()
 	defer f.flagsMu.Unlock()
 	if f.async == nil && newAsync != nil {
 		f.async = newAsync()
 		if f.flags.Async {
-			f.async.Register(f)
+			if err := f.async.Register(f); err != nil {
+				return nil, err
+			}
 		}
 	}
-	return f.async
+	return f.async, nil
 }
 
 // lockedReader implements io.Reader and io.ReaderAt.

pkg/sentry/fs/file_overlay.go

@@ -100,14 +100,13 @@ func (f *overlayFileOperations) Release(ctx context.Context) {
 }
 
 // EventRegister implements FileOperations.EventRegister.
-func (f *overlayFileOperations) EventRegister(we *waiter.Entry) {
+func (f *overlayFileOperations) EventRegister(we *waiter.Entry) error {
 	f.upperMu.Lock()
 	defer f.upperMu.Unlock()
 	if f.upper != nil {
-		f.upper.EventRegister(we)
-		return
+		return f.upper.EventRegister(we)
 	}
-	f.lower.EventRegister(we)
+	return f.lower.EventRegister(we)
 }
 
 // EventUnregister implements FileOperations.Unregister.

pkg/sentry/fs/file_state.go

@@ -14,6 +14,8 @@
 
 package fs
 
+import "fmt"
+
 // beforeSave is invoked by stateify.
 func (f *File) beforeSave() {
 	f.saving = true
@@ -25,6 +27,8 @@ func (f *File) beforeSave() {
 // afterLoad is invoked by stateify.
 func (f *File) afterLoad() {
 	if f.flags.Async && f.async != nil {
-		f.async.Register(f)
+		if err := f.async.Register(f); err != nil {
+			panic(fmt.Sprint("async.Register:", err))
+		}
 	}
 }

pkg/sentry/fs/host/file.go

@@ -149,15 +149,21 @@ func newFile(ctx context.Context, dirent *fs.Dirent, flags fs.FileFlags, iops *i
 }
 
 // EventRegister implements waiter.Waitable.EventRegister.
-func (f *fileOperations) EventRegister(e *waiter.Entry) {
+func (f *fileOperations) EventRegister(e *waiter.Entry) error {
 	f.iops.fileState.queue.EventRegister(e)
-	fdnotifier.UpdateFD(int32(f.iops.fileState.FD()))
+	if err := fdnotifier.UpdateFD(int32(f.iops.fileState.FD())); err != nil {
+		f.iops.fileState.queue.EventUnregister(e)
+		return err
+	}
+	return nil
 }
 
 // EventUnregister implements waiter.Waitable.EventUnregister.
 func (f *fileOperations) EventUnregister(e *waiter.Entry) {
 	f.iops.fileState.queue.EventUnregister(e)
-	fdnotifier.UpdateFD(int32(f.iops.fileState.FD()))
+	if err := fdnotifier.UpdateFD(int32(f.iops.fileState.FD())); err != nil {
+		panic(fmt.Sprint("UpdateFD:", err))
+	}
 }
 
 // Readiness uses the poll() syscall to check the status of the underlying FD.

pkg/sentry/fs/host/socket.go

@@ -259,12 +259,15 @@ func (c *ConnectedEndpoint) GetLocalAddress() (tcpip.FullAddress, tcpip.Error) {
 }
 
 // EventUpdate implements transport.ConnectedEndpoint.EventUpdate.
-func (c *ConnectedEndpoint) EventUpdate() {
+func (c *ConnectedEndpoint) EventUpdate() error {
 	c.mu.RLock()
 	defer c.mu.RUnlock()
 	if c.file.FD() != -1 {
-		fdnotifier.UpdateFD(int32(c.file.FD()))
+		if err := fdnotifier.UpdateFD(int32(c.file.FD())); err != nil {
+			return err
+		}
 	}
+	return nil
 }
 
 // Recv implements transport.Receiver.Recv.

pkg/sentry/fs/inotify.go

@@ -351,3 +351,9 @@ func (i *Inotify) RmWatch(ctx context.Context, wd int32) error {
 
 	return nil
 }
+
+// EventRegister implements waiter.Waitable.
+func (i *Inotify) EventRegister(e *waiter.Entry) error {
+	i.Queue.EventRegister(e)
+	return nil
+}

pkg/sentry/fs/timerfd/timerfd.go

@@ -108,8 +108,9 @@ func (t *TimerOperations) Readiness(mask waiter.EventMask) waiter.EventMask {
 }
 
 // EventRegister implements waiter.Waitable.EventRegister.
-func (t *TimerOperations) EventRegister(e *waiter.Entry) {
+func (t *TimerOperations) EventRegister(e *waiter.Entry) error {
 	t.events.EventRegister(e)
+	return nil
 }
 
 // EventUnregister implements waiter.Waitable.EventUnregister.

pkg/sentry/fs/tty/master.go

@@ -128,8 +128,9 @@ func (mf *masterFileOperations) Release(ctx context.Context) {
 }
 
 // EventRegister implements waiter.Waitable.EventRegister.
-func (mf *masterFileOperations) EventRegister(e *waiter.Entry) {
+func (mf *masterFileOperations) EventRegister(e *waiter.Entry) error {
 	mf.t.ld.masterWaiter.EventRegister(e)
+	return nil
 }
 
 // EventUnregister implements waiter.Waitable.EventUnregister.

pkg/sentry/fs/tty/replica.go

@@ -113,8 +113,9 @@ func (sf *replicaFileOperations) Release(context.Context) {
 }
 
 // EventRegister implements waiter.Waitable.EventRegister.
-func (sf *replicaFileOperations) EventRegister(e *waiter.Entry) {
+func (sf *replicaFileOperations) EventRegister(e *waiter.Entry) error {
 	sf.si.t.ld.replicaWaiter.EventRegister(e)
+	return nil
 }
 
 // EventUnregister implements waiter.Waitable.EventUnregister.

pkg/sentry/fsimpl/devpts/master.go

@@ -103,8 +103,9 @@ func (mfd *masterFileDescription) Release(ctx context.Context) {
 }
 
 // EventRegister implements waiter.Waitable.EventRegister.
-func (mfd *masterFileDescription) EventRegister(e *waiter.Entry) {
+func (mfd *masterFileDescription) EventRegister(e *waiter.Entry) error {
 	mfd.t.ld.masterWaiter.EventRegister(e)
+	return nil
 }
 
 // EventUnregister implements waiter.Waitable.EventUnregister.

pkg/sentry/fsimpl/devpts/replica.go

@@ -112,8 +112,9 @@ var _ vfs.FileDescriptionImpl = (*replicaFileDescription)(nil)
 func (rfd *replicaFileDescription) Release(ctx context.Context) {}
 
 // EventRegister implements waiter.Waitable.EventRegister.
-func (rfd *replicaFileDescription) EventRegister(e *waiter.Entry) {
+func (rfd *replicaFileDescription) EventRegister(e *waiter.Entry) error {
 	rfd.inode.t.ld.replicaWaiter.EventRegister(e)
+	return nil
 }
 
 // EventUnregister implements waiter.Waitable.EventUnregister.

pkg/sentry/fsimpl/eventfd/eventfd.go

@@ -16,6 +16,7 @@
 package eventfd
 
 import (
+	"fmt"
 	"math"
 	"sync"
 
@@ -266,14 +267,18 @@ func (efd *EventFileDescription) Readiness(mask waiter.EventMask) waiter.EventMa
 }
 
 // EventRegister implements waiter.Waitable.EventRegister.
-func (efd *EventFileDescription) EventRegister(entry *waiter.Entry) {
+func (efd *EventFileDescription) EventRegister(entry *waiter.Entry) error {
 	efd.queue.EventRegister(entry)
 
 	efd.mu.Lock()
 	defer efd.mu.Unlock()
 	if efd.hostfd >= 0 {
-		fdnotifier.UpdateFD(int32(efd.hostfd))
+		if err := fdnotifier.UpdateFD(int32(efd.hostfd)); err != nil {
+			efd.queue.EventUnregister(entry)
+			return err
+		}
 	}
+	return nil
 }
 
 // EventUnregister implements waiter.Waitable.EventUnregister.
@@ -283,6 +288,8 @@ func (efd *EventFileDescription) EventUnregister(entry *waiter.Entry) {
 	efd.mu.Lock()
 	defer efd.mu.Unlock()
 	if efd.hostfd >= 0 {
-		fdnotifier.UpdateFD(int32(efd.hostfd))
+		if err := fdnotifier.UpdateFD(int32(efd.hostfd)); err != nil {
+			panic(fmt.Sprint("UpdateFD:", err))
+		}
 	}
 }

pkg/sentry/fsimpl/eventfd/eventfd_test.go

@@ -49,7 +49,9 @@ func TestEventFD(t *testing.T) {
 
 		// Register a callback for a write event.
 		w, ch := waiter.NewChannelEntry(waiter.ReadableEvents)
-		eventfd.EventRegister(&w)
+		if err := eventfd.EventRegister(&w); err != nil {
+			t.Fatalf("EventRegister(): %v", err)
+		}
 		defer eventfd.EventUnregister(&w)
 
 		data := []byte("00000124")

pkg/sentry/fsimpl/fuse/dev.go

@@ -378,8 +378,9 @@ func (fd *DeviceFD) readinessLocked(mask waiter.EventMask) waiter.EventMask {
 }
 
 // EventRegister implements waiter.Waitable.EventRegister.
-func (fd *DeviceFD) EventRegister(e *waiter.Entry) {
+func (fd *DeviceFD) EventRegister(e *waiter.Entry) error {
 	fd.waitQueue.EventRegister(e)
+	return nil
 }
 
 // EventUnregister implements waiter.Waitable.EventUnregister.

pkg/sentry/fsimpl/gofer/special_file.go

@@ -15,6 +15,7 @@
 package gofer
 
 import (
+	"fmt"
 	"sync/atomic"
 
 	"golang.org/x/sys/unix"
@@ -165,20 +166,25 @@ func (fd *specialFileFD) Readiness(mask waiter.EventMask) waiter.EventMask {
 }
 
 // EventRegister implements waiter.Waitable.EventRegister.
-func (fd *specialFileFD) EventRegister(e *waiter.Entry) {
+func (fd *specialFileFD) EventRegister(e *waiter.Entry) error {
 	if fd.haveQueue {
 		fd.queue.EventRegister(e)
-		fdnotifier.UpdateFD(fd.handle.fd)
-		return
+		if err := fdnotifier.UpdateFD(fd.handle.fd); err != nil {
+			fd.queue.EventUnregister(e)
+			return err
+		}
+		return nil
 	}
-	fd.fileDescription.EventRegister(e)
+	return fd.fileDescription.EventRegister(e)
 }
 
 // EventUnregister implements waiter.Waitable.EventUnregister.
 func (fd *specialFileFD) EventUnregister(e *waiter.Entry) {
 	if fd.haveQueue {
 		fd.queue.EventUnregister(e)
-		fdnotifier.UpdateFD(fd.handle.fd)
+		if err := fdnotifier.UpdateFD(fd.handle.fd); err != nil {
+			panic(fmt.Sprint("UpdateFD:", err))
+		}
 		return
 	}
 	fd.fileDescription.EventUnregister(e)