Support pipes and sockets in VFS2 gofer fs.

Named pipes and sockets can be represented in two ways in gofer fs:
1. As a file on the remote filesystem. In this case, all file operations are
   passed through 9p.
2. As a synthetic file that is internal to the sandbox. In this case, the
   dentry stores an endpoint or VFSPipe for sockets and pipes respectively,
   which replaces interactions with the remote fs through the gofer.
In gofer.filesystem.MknodAt, we attempt to call mknod(2) through 9p,
and if it fails, fall back to the synthetic version.

Updates #1200.

PiperOrigin-RevId: 308828161

1 files changed, 141 insertions, 0 deletions

diff --git a/pkg/sentry/fsimpl/gofer/socket.go b/pkg/sentry/fsimpl/gofer/socket.go
new file mode 100644
index 000000000..73835df91
--- /dev/null
+++ b/pkg/sentry/fsimpl/gofer/socket.go
@@ -0,0 +1,141 @@
+// 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 gofer
+
+import (
+	"syscall"
+
+	"gvisor.dev/gvisor/pkg/abi/linux"
+	"gvisor.dev/gvisor/pkg/context"
+	"gvisor.dev/gvisor/pkg/log"
+	"gvisor.dev/gvisor/pkg/p9"
+	"gvisor.dev/gvisor/pkg/sentry/fsimpl/host"
+	"gvisor.dev/gvisor/pkg/sentry/socket/unix/transport"
+	"gvisor.dev/gvisor/pkg/syserr"
+	"gvisor.dev/gvisor/pkg/waiter"
+)
+
+func (d *dentry) isSocket() bool {
+	return d.fileType() == linux.S_IFSOCK
+}
+
+// endpoint is a Gofer-backed transport.BoundEndpoint.
+//
+// An endpoint's lifetime is the time between when filesystem.BoundEndpointAt()
+// is called and either BoundEndpoint.BidirectionalConnect or
+// BoundEndpoint.UnidirectionalConnect is called.
+type endpoint struct {
+	// dentry is the filesystem dentry which produced this endpoint.
+	dentry *dentry
+
+	// file is the p9 file that contains a single unopened fid.
+	file p9.File
+
+	// path is the sentry path where this endpoint is bound.
+	path string
+}
+
+func sockTypeToP9(t linux.SockType) (p9.ConnectFlags, bool) {
+	switch t {
+	case linux.SOCK_STREAM:
+		return p9.StreamSocket, true
+	case linux.SOCK_SEQPACKET:
+		return p9.SeqpacketSocket, true
+	case linux.SOCK_DGRAM:
+		return p9.DgramSocket, true
+	}
+	return 0, false
+}
+
+// BidirectionalConnect implements ConnectableEndpoint.BidirectionalConnect.
+func (e *endpoint) BidirectionalConnect(ctx context.Context, ce transport.ConnectingEndpoint, returnConnect func(transport.Receiver, transport.ConnectedEndpoint)) *syserr.Error {
+	cf, ok := sockTypeToP9(ce.Type())
+	if !ok {
+		return syserr.ErrConnectionRefused
+	}
+
+	// No lock ordering required as only the ConnectingEndpoint has a mutex.
+	ce.Lock()
+
+	// Check connecting state.
+	if ce.Connected() {
+		ce.Unlock()
+		return syserr.ErrAlreadyConnected
+	}
+	if ce.Listening() {
+		ce.Unlock()
+		return syserr.ErrInvalidEndpointState
+	}
+
+	c, err := e.newConnectedEndpoint(ctx, cf, ce.WaiterQueue())
+	if err != nil {
+		ce.Unlock()
+		return err
+	}
+
+	returnConnect(c, c)
+	ce.Unlock()
+	c.Init()
+
+	return nil
+}
+
+// UnidirectionalConnect implements
+// transport.BoundEndpoint.UnidirectionalConnect.
+func (e *endpoint) UnidirectionalConnect(ctx context.Context) (transport.ConnectedEndpoint, *syserr.Error) {
+	c, err := e.newConnectedEndpoint(ctx, p9.DgramSocket, &waiter.Queue{})
+	if err != nil {
+		return nil, err
+	}
+	c.Init()
+
+	// We don't need the receiver.
+	c.CloseRecv()
+	c.Release()
+
+	return c, nil
+}
+
+func (e *endpoint) newConnectedEndpoint(ctx context.Context, flags p9.ConnectFlags, queue *waiter.Queue) (*host.SCMConnectedEndpoint, *syserr.Error) {
+	hostFile, err := e.file.Connect(flags)
+	if err != nil {
+		return nil, syserr.ErrConnectionRefused
+	}
+	// Dup the fd so that the new endpoint can manage its lifetime.
+	hostFD, err := syscall.Dup(hostFile.FD())
+	if err != nil {
+		log.Warningf("Could not dup host socket fd %d: %v", hostFile.FD(), err)
+		return nil, syserr.FromError(err)
+	}
+	// After duplicating, we no longer need hostFile.
+	hostFile.Close()
+
+	c, serr := host.NewSCMEndpoint(ctx, hostFD, queue, e.path)
+	if serr != nil {
+		log.Warningf("Gofer returned invalid host socket for BidirectionalConnect; file %+v flags %+v: %v", e.file, flags, serr)
+		return nil, serr
+	}
+	return c, nil
+}
+
+// Release implements transport.BoundEndpoint.Release.
+func (e *endpoint) Release() {
+	e.dentry.DecRef()
+}
+
+// Passcred implements transport.BoundEndpoint.Passcred.
+func (e *endpoint) Passcred() bool {
+	return false
+}