2 files changed, 155 insertions, 0 deletions
diff --git a/pkg/sentry/fsimpl/signalfd/BUILD b/pkg/sentry/fsimpl/signalfd/BUILD
new file mode 100644
index 000000000..067c1657f
--- /dev/null
+++ b/pkg/sentry/fsimpl/signalfd/BUILD
@@ -0,0 +1,20 @@
+load("//tools:defs.bzl", "go_library")
+
+package(licenses = ["notice"])
+
+go_library(
+    name = "signalfd",
+    srcs = ["signalfd.go"],
+    visibility = ["//pkg/sentry:internal"],
+    deps = [
+        "//pkg/abi/linux",
+        "//pkg/binary",
+        "//pkg/context",
+        "//pkg/sentry/kernel",
+        "//pkg/sentry/vfs",
+        "//pkg/sync",
+        "//pkg/syserror",
+        "//pkg/usermem",
+        "//pkg/waiter",
+    ],
+)
diff --git a/pkg/sentry/fsimpl/signalfd/signalfd.go b/pkg/sentry/fsimpl/signalfd/signalfd.go
new file mode 100644
index 000000000..d29ef3f83
--- /dev/null
+++ b/pkg/sentry/fsimpl/signalfd/signalfd.go
@@ -0,0 +1,135 @@
+// Copyright 2019 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 signalfd
+
+import (
+	"gvisor.dev/gvisor/pkg/abi/linux"
+	"gvisor.dev/gvisor/pkg/binary"
+	"gvisor.dev/gvisor/pkg/context"
+	"gvisor.dev/gvisor/pkg/sentry/kernel"
+	"gvisor.dev/gvisor/pkg/sentry/vfs"
+	"gvisor.dev/gvisor/pkg/sync"
+	"gvisor.dev/gvisor/pkg/syserror"
+	"gvisor.dev/gvisor/pkg/usermem"
+	"gvisor.dev/gvisor/pkg/waiter"
+)
+
+// SignalFileDescription implements FileDescriptionImpl for signal fds.
+type SignalFileDescription struct {
+	vfsfd vfs.FileDescription
+	vfs.FileDescriptionDefaultImpl
+	vfs.DentryMetadataFileDescriptionImpl
+
+	// target is the original signal target task.
+	//
+	// The semantics here are a bit broken. Linux will always use current
+	// for all reads, regardless of where the signalfd originated. We can't
+	// do exactly that because we need to plumb the context through
+	// EventRegister in order to support proper blocking behavior. This
+	// will undoubtedly become very complicated quickly.
+	target *kernel.Task
+
+	// mu protects mask.
+	mu sync.Mutex
+
+	// mask is the signal mask. Protected by mu.
+	mask linux.SignalSet
+}
+
+var _ vfs.FileDescriptionImpl = (*SignalFileDescription)(nil)
+
+// New creates a new signal fd.
+func New(vfsObj *vfs.VirtualFilesystem, target *kernel.Task, mask linux.SignalSet, flags uint32) (*vfs.FileDescription, error) {
+	vd := vfsObj.NewAnonVirtualDentry("[signalfd]")
+	defer vd.DecRef()
+	sfd := &SignalFileDescription{
+		target: target,
+		mask:   mask,
+	}
+	if err := sfd.vfsfd.Init(sfd, flags, vd.Mount(), vd.Dentry(), &vfs.FileDescriptionOptions{
+		UseDentryMetadata: true,
+		DenyPRead:         true,
+		DenyPWrite:        true,
+	}); err != nil {
+		return nil, err
+	}
+	return &sfd.vfsfd, nil
+}
+
+// Mask returns the signal mask.
+func (sfd *SignalFileDescription) Mask() linux.SignalSet {
+	sfd.mu.Lock()
+	defer sfd.mu.Unlock()
+	return sfd.mask
+}
+
+// SetMask sets the signal mask.
+func (sfd *SignalFileDescription) SetMask(mask linux.SignalSet) {
+	sfd.mu.Lock()
+	defer sfd.mu.Unlock()
+	sfd.mask = mask
+}
+
+// Read implements FileDescriptionImpl.Read.
+func (sfd *SignalFileDescription) Read(ctx context.Context, dst usermem.IOSequence, _ vfs.ReadOptions) (int64, error) {
+	// Attempt to dequeue relevant signals.
+	info, err := sfd.target.Sigtimedwait(sfd.Mask(), 0)
+	if err != nil {
+		// There must be no signal available.
+		return 0, syserror.ErrWouldBlock
+	}
+
+	// Copy out the signal info using the specified format.
+	var buf [128]byte
+	binary.Marshal(buf[:0], usermem.ByteOrder, &linux.SignalfdSiginfo{
+		Signo:   uint32(info.Signo),
+		Errno:   info.Errno,
+		Code:    info.Code,
+		PID:     uint32(info.Pid()),
+		UID:     uint32(info.Uid()),
+		Status:  info.Status(),
+		Overrun: uint32(info.Overrun()),
+		Addr:    info.Addr(),
+	})
+	n, err := dst.CopyOut(ctx, buf[:])
+	return int64(n), err
+}
+
+// Readiness implements waiter.Waitable.Readiness.
+func (sfd *SignalFileDescription) Readiness(mask waiter.EventMask) waiter.EventMask {
+	sfd.mu.Lock()
+	defer sfd.mu.Unlock()
+	if mask&waiter.EventIn != 0 && sfd.target.PendingSignals()&sfd.mask != 0 {
+		return waiter.EventIn // Pending signals.
+	}
+	return 0
+}
+
+// EventRegister implements waiter.Waitable.EventRegister.
+func (sfd *SignalFileDescription) EventRegister(entry *waiter.Entry, _ waiter.EventMask) {
+	sfd.mu.Lock()
+	defer sfd.mu.Unlock()
+	// Register for the signal set; ignore the passed events.
+	sfd.target.SignalRegister(entry, waiter.EventMask(sfd.mask))
+}
+
+// EventUnregister implements waiter.Waitable.EventUnregister.
+func (sfd *SignalFileDescription) EventUnregister(entry *waiter.Entry) {
+	// Unregister the original entry.
+	sfd.target.SignalUnregister(entry)
+}
+
+// Release implements FileDescriptionImpl.Release()
+func (sfd *SignalFileDescription) Release() {}