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// Copyright 2018 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 kernel
import (
"fmt"
"golang.org/x/sys/unix"
"gvisor.dev/gvisor/pkg/context"
"gvisor.dev/gvisor/pkg/refs"
"gvisor.dev/gvisor/pkg/sentry/socket/unix/transport"
"gvisor.dev/gvisor/pkg/sync"
)
// +stateify savable
type abstractEndpoint struct {
ep transport.BoundEndpoint
socket refs.TryRefCounter
name string
ns *AbstractSocketNamespace
}
// AbstractSocketNamespace is used to implement the Linux abstract socket functionality.
//
// +stateify savable
type AbstractSocketNamespace struct {
mu sync.Mutex `state:"nosave"`
// Keeps a mapping from name to endpoint. AbstractSocketNamespace does not hold
// any references on any sockets that it contains; when retrieving a socket,
// TryIncRef() must be called in case the socket is concurrently being
// destroyed. It is the responsibility of the socket to remove itself from the
// abstract socket namespace when it is destroyed.
endpoints map[string]abstractEndpoint
}
// NewAbstractSocketNamespace returns a new AbstractSocketNamespace.
func NewAbstractSocketNamespace() *AbstractSocketNamespace {
return &AbstractSocketNamespace{
endpoints: make(map[string]abstractEndpoint),
}
}
// A boundEndpoint wraps a transport.BoundEndpoint to maintain a reference on
// its backing socket.
type boundEndpoint struct {
transport.BoundEndpoint
socket refs.TryRefCounter
}
// Release implements transport.BoundEndpoint.Release.
func (e *boundEndpoint) Release(ctx context.Context) {
e.socket.DecRef(ctx)
e.BoundEndpoint.Release(ctx)
}
// BoundEndpoint retrieves the endpoint bound to the given name. The return
// value is nil if no endpoint was bound.
func (a *AbstractSocketNamespace) BoundEndpoint(name string) transport.BoundEndpoint {
a.mu.Lock()
defer a.mu.Unlock()
ep, ok := a.endpoints[name]
if !ok {
return nil
}
if !ep.socket.TryIncRef() {
// The socket has reached zero references and is being destroyed.
return nil
}
return &boundEndpoint{ep.ep, ep.socket}
}
// Bind binds the given socket.
//
// When the last reference managed by socket is dropped, ep may be removed from the
// namespace.
func (a *AbstractSocketNamespace) Bind(ctx context.Context, name string, ep transport.BoundEndpoint, socket refs.TryRefCounter) error {
a.mu.Lock()
defer a.mu.Unlock()
// Check if there is already a socket (which has not yet been destroyed) bound at name.
if ep, ok := a.endpoints[name]; ok {
if ep.socket.TryIncRef() {
ep.socket.DecRef(ctx)
return unix.EADDRINUSE
}
}
ae := abstractEndpoint{ep: ep, name: name, ns: a}
ae.socket = socket
a.endpoints[name] = ae
return nil
}
// Remove removes the specified socket at name from the abstract socket
// namespace, if it has not yet been replaced.
func (a *AbstractSocketNamespace) Remove(name string, socket refs.TryRefCounter) {
a.mu.Lock()
defer a.mu.Unlock()
ep, ok := a.endpoints[name]
if !ok {
// We never delete a map entry apart from a socket's destructor (although the
// map entry may be overwritten). Therefore, a socket should exist, even if it
// may not be the one we expect.
panic(fmt.Sprintf("expected socket to exist at '%s' in abstract socket namespace", name))
}
// A Bind() operation may race with callers of Remove(), e.g. in the
// following case:
// socket1 reaches zero references and begins destruction
// a.Bind("foo", ep, socket2) replaces socket1 with socket2
// socket1's destructor calls a.Remove("foo", socket1)
//
// Therefore, we need to check that the socket at name is what we expect
// before modifying the map.
if ep.socket == socket {
delete(a.endpoints, name)
}
}
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