3 files changed, 151 insertions, 0 deletions
diff --git a/pkg/sentry/vfs/BUILD b/pkg/sentry/vfs/BUILD
index bf4d27c7d..9aeb83fb0 100644
--- a/pkg/sentry/vfs/BUILD
+++ b/pkg/sentry/vfs/BUILD
@@ -36,6 +36,7 @@ go_library(
         "pathname.go",
         "permissions.go",
         "resolving_path.go",
+        "timerfd.go",
         "vfs.go",
     ],
     visibility = ["//pkg/sentry:internal"],
@@ -51,6 +52,7 @@ go_library(
         "//pkg/sentry/fs",
         "//pkg/sentry/fs/lock",
         "//pkg/sentry/kernel/auth",
+        "//pkg/sentry/kernel/time",
         "//pkg/sentry/limits",
         "//pkg/sentry/memmap",
         "//pkg/sentry/socket/unix/transport",
diff --git a/pkg/sentry/vfs/file_description.go b/pkg/sentry/vfs/file_description.go
index 28e93a441..20c545fca 100644
--- a/pkg/sentry/vfs/file_description.go
+++ b/pkg/sentry/vfs/file_description.go
@@ -91,6 +91,10 @@ type FileDescriptionOptions struct {
 	// ESPIPE.
 	DenyPWrite bool
 
+	// if InvalidWrite is true, calls to FileDescription.Write() return
+	// EINVAL.
+	InvalidWrite bool
+
 	// If UseDentryMetadata is true, calls to FileDescription methods that
 	// interact with file and filesystem metadata (Stat, SetStat, StatFS,
 	// Listxattr, Getxattr, Setxattr, Removexattr) are implemented by calling
@@ -562,6 +566,9 @@ func (fd *FileDescription) PWrite(ctx context.Context, src usermem.IOSequence, o
 
 // Write is similar to PWrite, but does not specify an offset.
 func (fd *FileDescription) Write(ctx context.Context, src usermem.IOSequence, opts WriteOptions) (int64, error) {
+	if fd.opts.InvalidWrite {
+		return 0, syserror.EINVAL
+	}
 	if !fd.writable {
 		return 0, syserror.EBADF
 	}
diff --git a/pkg/sentry/vfs/timerfd.go b/pkg/sentry/vfs/timerfd.go
new file mode 100644
index 000000000..42b880656
--- /dev/null
+++ b/pkg/sentry/vfs/timerfd.go
@@ -0,0 +1,142 @@
+// Copyright 2020 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package vfs
+
+import (
+	"sync/atomic"
+
+	"gvisor.dev/gvisor/pkg/context"
+	ktime "gvisor.dev/gvisor/pkg/sentry/kernel/time"
+	"gvisor.dev/gvisor/pkg/syserror"
+	"gvisor.dev/gvisor/pkg/usermem"
+	"gvisor.dev/gvisor/pkg/waiter"
+)
+
+// TimerFileDescription implements FileDescriptionImpl for timer fds. It also
+// implements ktime.TimerListener.
+type TimerFileDescription struct {
+	vfsfd FileDescription
+	FileDescriptionDefaultImpl
+	DentryMetadataFileDescriptionImpl
+
+	events waiter.Queue
+	timer  *ktime.Timer
+
+	// val is the number of timer expirations since the last successful
+	// call to PRead, or SetTime. val must be accessed using atomic memory
+	// operations.
+	val uint64
+}
+
+var _ FileDescriptionImpl = (*TimerFileDescription)(nil)
+var _ ktime.TimerListener = (*TimerFileDescription)(nil)
+
+// NewTimerFD returns a new timer fd.
+func (vfs *VirtualFilesystem) NewTimerFD(clock ktime.Clock, flags uint32) (*FileDescription, error) {
+	vd := vfs.NewAnonVirtualDentry("[timerfd]")
+	defer vd.DecRef()
+	tfd := &TimerFileDescription{}
+	tfd.timer = ktime.NewTimer(clock, tfd)
+	if err := tfd.vfsfd.Init(tfd, flags, vd.Mount(), vd.Dentry(), &FileDescriptionOptions{
+		UseDentryMetadata: true,
+		DenyPRead:         true,
+		DenyPWrite:        true,
+		InvalidWrite:      true,
+	}); err != nil {
+		return nil, err
+	}
+	return &tfd.vfsfd, nil
+}
+
+// Read implements FileDescriptionImpl.Read.
+func (tfd *TimerFileDescription) Read(ctx context.Context, dst usermem.IOSequence, opts ReadOptions) (int64, error) {
+	const sizeofUint64 = 8
+	if dst.NumBytes() < sizeofUint64 {
+		return 0, syserror.EINVAL
+	}
+	if val := atomic.SwapUint64(&tfd.val, 0); val != 0 {
+		var buf [sizeofUint64]byte
+		usermem.ByteOrder.PutUint64(buf[:], val)
+		if _, err := dst.CopyOut(ctx, buf[:]); err != nil {
+			// Linux does not undo consuming the number of
+			// expirations even if writing to userspace fails.
+			return 0, err
+		}
+		return sizeofUint64, nil
+	}
+	return 0, syserror.ErrWouldBlock
+}
+
+// Clock returns the timer fd's Clock.
+func (tfd *TimerFileDescription) Clock() ktime.Clock {
+	return tfd.timer.Clock()
+}
+
+// GetTime returns the associated Timer's setting and the time at which it was
+// observed.
+func (tfd *TimerFileDescription) GetTime() (ktime.Time, ktime.Setting) {
+	return tfd.timer.Get()
+}
+
+// SetTime atomically changes the associated Timer's setting, resets the number
+// of expirations to 0, and returns the previous setting and the time at which
+// it was observed.
+func (tfd *TimerFileDescription) SetTime(s ktime.Setting) (ktime.Time, ktime.Setting) {
+	return tfd.timer.SwapAnd(s, func() { atomic.StoreUint64(&tfd.val, 0) })
+}
+
+// Readiness implements waiter.Waitable.Readiness.
+func (tfd *TimerFileDescription) Readiness(mask waiter.EventMask) waiter.EventMask {
+	var ready waiter.EventMask
+	if atomic.LoadUint64(&tfd.val) != 0 {
+		ready |= waiter.EventIn
+	}
+	return ready
+}
+
+// EventRegister implements waiter.Waitable.EventRegister.
+func (tfd *TimerFileDescription) EventRegister(e *waiter.Entry, mask waiter.EventMask) {
+	tfd.events.EventRegister(e, mask)
+}
+
+// EventUnregister implements waiter.Waitable.EventUnregister.
+func (tfd *TimerFileDescription) EventUnregister(e *waiter.Entry) {
+	tfd.events.EventUnregister(e)
+}
+
+// PauseTimer pauses the associated Timer.
+func (tfd *TimerFileDescription) PauseTimer() {
+	tfd.timer.Pause()
+}
+
+// ResumeTimer resumes the associated Timer.
+func (tfd *TimerFileDescription) ResumeTimer() {
+	tfd.timer.Resume()
+}
+
+// Release implements FileDescriptionImpl.Release()
+func (tfd *TimerFileDescription) Release() {
+	tfd.timer.Destroy()
+}
+
+// Notify implements ktime.TimerListener.Notify.
+func (tfd *TimerFileDescription) Notify(exp uint64, setting ktime.Setting) (ktime.Setting, bool) {
+	atomic.AddUint64(&tfd.val, exp)
+	tfd.events.Notify(waiter.EventIn)
+	return ktime.Setting{}, false
+}
+
+// Destroy implements ktime.TimerListener.Destroy.
+func (tfd *TimerFileDescription) Destroy() {}