2 files changed, 127 insertions, 0 deletions
diff --git a/pkg/sentry/fsimpl/sockfs/BUILD b/pkg/sentry/fsimpl/sockfs/BUILD
new file mode 100644
index 000000000..9453277b8
--- /dev/null
+++ b/pkg/sentry/fsimpl/sockfs/BUILD
@@ -0,0 +1,18 @@
+load("//tools:defs.bzl", "go_library")
+
+licenses(["notice"])
+
+go_library(
+    name = "sockfs",
+    srcs = ["sockfs.go"],
+    visibility = ["//pkg/sentry:internal"],
+    deps = [
+        "//pkg/abi/linux",
+        "//pkg/context",
+        "//pkg/fspath",
+        "//pkg/sentry/fsimpl/kernfs",
+        "//pkg/sentry/kernel/auth",
+        "//pkg/sentry/vfs",
+        "//pkg/syserror",
+    ],
+)
diff --git a/pkg/sentry/fsimpl/sockfs/sockfs.go b/pkg/sentry/fsimpl/sockfs/sockfs.go
new file mode 100644
index 000000000..c61818ff6
--- /dev/null
+++ b/pkg/sentry/fsimpl/sockfs/sockfs.go
@@ -0,0 +1,109 @@
+// 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 sockfs provides a filesystem implementation for anonymous sockets.
+package sockfs
+
+import (
+	"fmt"
+
+	"gvisor.dev/gvisor/pkg/abi/linux"
+	"gvisor.dev/gvisor/pkg/context"
+	"gvisor.dev/gvisor/pkg/fspath"
+	"gvisor.dev/gvisor/pkg/sentry/fsimpl/kernfs"
+	"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
+	"gvisor.dev/gvisor/pkg/sentry/vfs"
+	"gvisor.dev/gvisor/pkg/syserror"
+)
+
+// filesystemType implements vfs.FilesystemType.
+type filesystemType struct{}
+
+// GetFilesystem implements FilesystemType.GetFilesystem.
+func (fsType filesystemType) GetFilesystem(_ context.Context, vfsObj *vfs.VirtualFilesystem, _ *auth.Credentials, _ string, _ vfs.GetFilesystemOptions) (*vfs.Filesystem, *vfs.Dentry, error) {
+	panic("sockfs.filesystemType.GetFilesystem should never be called")
+}
+
+// Name implements FilesystemType.Name.
+//
+// Note that registering sockfs is unnecessary, except for the fact that it
+// will not show up under /proc/filesystems as a result. This is a very minor
+// discrepancy from Linux.
+func (filesystemType) Name() string {
+	return "sockfs"
+}
+
+type filesystem struct {
+	kernfs.Filesystem
+
+	devMinor uint32
+}
+
+// NewFilesystem sets up and returns a new sockfs filesystem.
+//
+// Note that there should only ever be one instance of sockfs.Filesystem,
+// backing a global socket mount.
+func NewFilesystem(vfsObj *vfs.VirtualFilesystem) (*vfs.Filesystem, error) {
+	devMinor, err := vfsObj.GetAnonBlockDevMinor()
+	if err != nil {
+		return nil, err
+	}
+	fs := &filesystem{
+		devMinor: devMinor,
+	}
+	fs.Filesystem.VFSFilesystem().Init(vfsObj, filesystemType{}, fs)
+	return fs.Filesystem.VFSFilesystem(), nil
+}
+
+// Release implements vfs.FilesystemImpl.Release.
+func (fs *filesystem) Release(ctx context.Context) {
+	fs.Filesystem.VFSFilesystem().VirtualFilesystem().PutAnonBlockDevMinor(fs.devMinor)
+	fs.Filesystem.Release(ctx)
+}
+
+// PrependPath implements vfs.FilesystemImpl.PrependPath.
+func (fs *filesystem) PrependPath(ctx context.Context, vfsroot, vd vfs.VirtualDentry, b *fspath.Builder) error {
+	inode := vd.Dentry().Impl().(*kernfs.Dentry).Inode().(*inode)
+	b.PrependComponent(fmt.Sprintf("socket:[%d]", inode.InodeAttrs.Ino()))
+	return vfs.PrependPathSyntheticError{}
+}
+
+// inode implements kernfs.Inode.
+type inode struct {
+	kernfs.InodeNotDirectory
+	kernfs.InodeNotSymlink
+	kernfs.InodeAttrs
+	kernfs.InodeNoopRefCount
+}
+
+// Open implements kernfs.Inode.Open.
+func (i *inode) Open(ctx context.Context, rp *vfs.ResolvingPath, vfsd *vfs.Dentry, opts vfs.OpenOptions) (*vfs.FileDescription, error) {
+	return nil, syserror.ENXIO
+}
+
+// NewDentry constructs and returns a sockfs dentry.
+//
+// Preconditions: mnt.Filesystem() must have been returned by NewFilesystem().
+func NewDentry(creds *auth.Credentials, mnt *vfs.Mount) *vfs.Dentry {
+	fs := mnt.Filesystem().Impl().(*filesystem)
+
+	// File mode matches net/socket.c:sock_alloc.
+	filemode := linux.FileMode(linux.S_IFSOCK | 0600)
+	i := &inode{}
+	i.InodeAttrs.Init(creds, linux.UNNAMED_MAJOR, fs.devMinor, fs.Filesystem.NextIno(), filemode)
+
+	d := &kernfs.Dentry{}
+	d.Init(i)
+	return d.VFSDentry()
+}