1 files changed, 392 insertions, 0 deletions
diff --git a/pkg/sentry/fsimpl/cgroupfs/cgroupfs.go b/pkg/sentry/fsimpl/cgroupfs/cgroupfs.go
new file mode 100644
index 000000000..3d4005fd8
--- /dev/null
+++ b/pkg/sentry/fsimpl/cgroupfs/cgroupfs.go
@@ -0,0 +1,392 @@
+// Copyright 2021 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 cgroupfs implements cgroupfs.
+//
+// A cgroup is a collection of tasks on the system, organized into a tree-like
+// structure similar to a filesystem directory tree. In fact, each cgroup is
+// represented by a directory on cgroupfs, and is manipulated through control
+// files in the directory.
+//
+// All cgroups on a system are organized into hierarchies. Hierarchies are a
+// distinct tree of cgroups, with a common set of controllers. One or more
+// cgroupfs mounts may point to each hierarchy. These mounts provide a common
+// view into the same tree of cgroups.
+//
+// A controller (also known as a "resource controller", or a cgroup "subsystem")
+// determines the behaviour of each cgroup.
+//
+// In addition to cgroupfs, the kernel has a cgroup registry that tracks
+// system-wide state related to cgroups such as active hierarchies and the
+// controllers associated with them.
+//
+// Since cgroupfs doesn't allow hardlinks, there is a unique mapping between
+// cgroupfs dentries and inodes.
+//
+// # Synchronization
+//
+// Cgroup hierarchy creation and destruction is protected by the
+// kernel.CgroupRegistry.mu. Once created, a hierarchy's set of controllers, the
+// filesystem associated with it, and the root cgroup for the hierarchy are
+// immutable.
+//
+// Membership of tasks within cgroups is protected by
+// cgroupfs.filesystem.tasksMu. Tasks also maintain a set of all cgroups they're
+// in, and this list is protected by Task.mu.
+//
+// Lock order:
+//
+// kernel.CgroupRegistry.mu
+//   cgroupfs.filesystem.mu
+//     Task.mu
+//       cgroupfs.filesystem.tasksMu.
+package cgroupfs
+
+import (
+	"fmt"
+	"sort"
+	"strconv"
+	"strings"
+
+	"gvisor.dev/gvisor/pkg/abi/linux"
+	"gvisor.dev/gvisor/pkg/context"
+	"gvisor.dev/gvisor/pkg/sentry/fsimpl/kernfs"
+	"gvisor.dev/gvisor/pkg/sentry/kernel"
+	"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
+	"gvisor.dev/gvisor/pkg/sentry/vfs"
+	"gvisor.dev/gvisor/pkg/sync"
+	"gvisor.dev/gvisor/pkg/syserror"
+)
+
+const (
+	// Name is the default filesystem name.
+	Name                     = "cgroup"
+	readonlyFileMode         = linux.FileMode(0444)
+	writableFileMode         = linux.FileMode(0644)
+	defaultMaxCachedDentries = uint64(1000)
+)
+
+const (
+	controllerCPU     = kernel.CgroupControllerType("cpu")
+	controllerCPUAcct = kernel.CgroupControllerType("cpuacct")
+	controllerCPUSet  = kernel.CgroupControllerType("cpuset")
+	controllerMemory  = kernel.CgroupControllerType("memory")
+)
+
+var allControllers = []kernel.CgroupControllerType{controllerCPU, controllerCPUAcct, controllerCPUSet, controllerMemory}
+
+// SupportedMountOptions is the set of supported mount options for cgroupfs.
+var SupportedMountOptions = []string{"all", "cpu", "cpuacct", "cpuset", "memory"}
+
+// FilesystemType implements vfs.FilesystemType.
+//
+// +stateify savable
+type FilesystemType struct{}
+
+// filesystem implements vfs.FilesystemImpl.
+//
+// +stateify savable
+type filesystem struct {
+	kernfs.Filesystem
+	devMinor uint32
+
+	// hierarchyID is the id the cgroup registry assigns to this hierarchy. Has
+	// the value kernel.InvalidCgroupHierarchyID until the FS is fully
+	// initialized.
+	//
+	// hierarchyID is immutable after initialization.
+	hierarchyID uint32
+
+	// controllers and kcontrollers are both the list of controllers attached to
+	// this cgroupfs. Both lists are the same set of controllers, but typecast
+	// to different interfaces for convenience. Both must stay in sync, and are
+	// immutable.
+	controllers  []controller
+	kcontrollers []kernel.CgroupController
+
+	numCgroups uint64 // Protected by atomic ops.
+
+	root *kernfs.Dentry
+
+	// tasksMu serializes task membership changes across all cgroups within a
+	// filesystem.
+	tasksMu sync.Mutex `state:"nosave"`
+}
+
+// Name implements vfs.FilesystemType.Name.
+func (FilesystemType) Name() string {
+	return Name
+}
+
+// Release implements vfs.FilesystemType.Release.
+func (FilesystemType) Release(ctx context.Context) {}
+
+// GetFilesystem implements vfs.FilesystemType.GetFilesystem.
+func (fsType FilesystemType) GetFilesystem(ctx context.Context, vfsObj *vfs.VirtualFilesystem, creds *auth.Credentials, source string, opts vfs.GetFilesystemOptions) (*vfs.Filesystem, *vfs.Dentry, error) {
+	devMinor, err := vfsObj.GetAnonBlockDevMinor()
+	if err != nil {
+		return nil, nil, err
+	}
+
+	mopts := vfs.GenericParseMountOptions(opts.Data)
+	maxCachedDentries := defaultMaxCachedDentries
+	if str, ok := mopts["dentry_cache_limit"]; ok {
+		delete(mopts, "dentry_cache_limit")
+		maxCachedDentries, err = strconv.ParseUint(str, 10, 64)
+		if err != nil {
+			ctx.Warningf("sys.FilesystemType.GetFilesystem: invalid dentry cache limit: dentry_cache_limit=%s", str)
+			return nil, nil, syserror.EINVAL
+		}
+	}
+
+	var wantControllers []kernel.CgroupControllerType
+	if _, ok := mopts["cpu"]; ok {
+		delete(mopts, "cpu")
+		wantControllers = append(wantControllers, controllerCPU)
+	}
+	if _, ok := mopts["cpuacct"]; ok {
+		delete(mopts, "cpuacct")
+		wantControllers = append(wantControllers, controllerCPUAcct)
+	}
+	if _, ok := mopts["cpuset"]; ok {
+		delete(mopts, "cpuset")
+		wantControllers = append(wantControllers, controllerCPUSet)
+	}
+	if _, ok := mopts["memory"]; ok {
+		delete(mopts, "memory")
+		wantControllers = append(wantControllers, controllerMemory)
+	}
+	if _, ok := mopts["all"]; ok {
+		if len(wantControllers) > 0 {
+			ctx.Debugf("cgroupfs.FilesystemType.GetFilesystem: other controllers specified with all: %v", wantControllers)
+			return nil, nil, syserror.EINVAL
+		}
+
+		delete(mopts, "all")
+		wantControllers = allControllers
+	}
+
+	if len(wantControllers) == 0 {
+		// Specifying no controllers implies all controllers.
+		wantControllers = allControllers
+	}
+
+	if len(mopts) != 0 {
+		ctx.Debugf("cgroupfs.FilesystemType.GetFilesystem: unknown options: %v", mopts)
+		return nil, nil, syserror.EINVAL
+	}
+
+	k := kernel.KernelFromContext(ctx)
+	r := k.CgroupRegistry()
+
+	// "It is not possible to mount the same controller against multiple
+	// cgroup hierarchies. For example, it is not possible to mount both
+	// the cpu and cpuacct controllers against one hierarchy, and to mount
+	// the cpu controller alone against another hierarchy." - man cgroups(7)
+	//
+	// Is there a hierarchy available with all the controllers we want? If so,
+	// this mount is a view into the same hierarchy.
+	//
+	// Note: we're guaranteed to have at least one requested controller, since
+	// no explicit controller name implies all controllers.
+	if vfsfs := r.FindHierarchy(wantControllers); vfsfs != nil {
+		fs := vfsfs.Impl().(*filesystem)
+		ctx.Debugf("cgroupfs.FilesystemType.GetFilesystem: mounting new view to hierarchy %v", fs.hierarchyID)
+		fs.root.IncRef()
+		return vfsfs, fs.root.VFSDentry(), nil
+	}
+
+	// No existing hierarchy with the exactly controllers found. Make a new
+	// one. Note that it's possible this mount creation is unsatisfiable, if one
+	// or more of the requested controllers are already on existing
+	// hierarchies. We'll find out about such collisions when we try to register
+	// the new hierarchy later.
+	fs := &filesystem{
+		devMinor: devMinor,
+	}
+	fs.MaxCachedDentries = maxCachedDentries
+	fs.VFSFilesystem().Init(vfsObj, &fsType, fs)
+
+	for _, ty := range wantControllers {
+		var c controller
+		switch ty {
+		case controllerMemory:
+			c = newMemoryController(fs)
+		case controllerCPU:
+			c = newCPUController(fs)
+		case controllerCPUAcct:
+			c = newCPUAcctController(fs)
+		case controllerCPUSet:
+			c = newCPUSetController(fs)
+		default:
+			panic(fmt.Sprintf("Unreachable: unknown cgroup controller %q", ty))
+		}
+		fs.controllers = append(fs.controllers, c)
+	}
+
+	// Controllers usually appear in alphabetical order when displayed. Sort it
+	// here now, so it never needs to be sorted elsewhere.
+	sort.Slice(fs.controllers, func(i, j int) bool { return fs.controllers[i].Type() < fs.controllers[j].Type() })
+	fs.kcontrollers = make([]kernel.CgroupController, 0, len(fs.controllers))
+	for _, c := range fs.controllers {
+		fs.kcontrollers = append(fs.kcontrollers, c)
+	}
+
+	root := fs.newCgroupInode(ctx, creds)
+	var rootD kernfs.Dentry
+	rootD.InitRoot(&fs.Filesystem, root)
+	fs.root = &rootD
+
+	// Register controllers. The registry may be modified concurrently, so if we
+	// get an error, we raced with someone else who registered the same
+	// controllers first.
+	hid, err := r.Register(fs.kcontrollers)
+	if err != nil {
+		ctx.Infof("cgroupfs.FilesystemType.GetFilesystem: failed to register new hierarchy with controllers %v: %v", wantControllers, err)
+		rootD.DecRef(ctx)
+		fs.VFSFilesystem().DecRef(ctx)
+		return nil, nil, syserror.EBUSY
+	}
+	fs.hierarchyID = hid
+
+	// Move all existing tasks to the root of the new hierarchy.
+	k.PopulateNewCgroupHierarchy(fs.rootCgroup())
+
+	return fs.VFSFilesystem(), rootD.VFSDentry(), nil
+}
+
+func (fs *filesystem) rootCgroup() kernel.Cgroup {
+	return kernel.Cgroup{
+		Dentry:     fs.root,
+		CgroupImpl: fs.root.Inode().(kernel.CgroupImpl),
+	}
+}
+
+// Release implements vfs.FilesystemImpl.Release.
+func (fs *filesystem) Release(ctx context.Context) {
+	k := kernel.KernelFromContext(ctx)
+	r := k.CgroupRegistry()
+
+	if fs.hierarchyID != kernel.InvalidCgroupHierarchyID {
+		k.ReleaseCgroupHierarchy(fs.hierarchyID)
+		r.Unregister(fs.hierarchyID)
+	}
+
+	fs.Filesystem.VFSFilesystem().VirtualFilesystem().PutAnonBlockDevMinor(fs.devMinor)
+	fs.Filesystem.Release(ctx)
+}
+
+// MountOptions implements vfs.FilesystemImpl.MountOptions.
+func (fs *filesystem) MountOptions() string {
+	var cnames []string
+	for _, c := range fs.controllers {
+		cnames = append(cnames, string(c.Type()))
+	}
+	return strings.Join(cnames, ",")
+}
+
+// +stateify savable
+type implStatFS struct{}
+
+// StatFS implements kernfs.Inode.StatFS.
+func (*implStatFS) StatFS(context.Context, *vfs.Filesystem) (linux.Statfs, error) {
+	return vfs.GenericStatFS(linux.CGROUP_SUPER_MAGIC), nil
+}
+
+// dir implements kernfs.Inode for a generic cgroup resource controller
+// directory. Specific controllers extend this to add their own functionality.
+//
+// +stateify savable
+type dir struct {
+	dirRefs
+	kernfs.InodeAlwaysValid
+	kernfs.InodeAttrs
+	kernfs.InodeNotSymlink
+	kernfs.InodeDirectoryNoNewChildren // TODO(b/183137098): Implement mkdir.
+	kernfs.OrderedChildren
+	implStatFS
+
+	locks vfs.FileLocks
+}
+
+// Keep implements kernfs.Inode.Keep.
+func (*dir) Keep() bool {
+	return true
+}
+
+// SetStat implements kernfs.Inode.SetStat not allowing inode attributes to be changed.
+func (*dir) SetStat(context.Context, *vfs.Filesystem, *auth.Credentials, vfs.SetStatOptions) error {
+	return syserror.EPERM
+}
+
+// Open implements kernfs.Inode.Open.
+func (d *dir) Open(ctx context.Context, rp *vfs.ResolvingPath, kd *kernfs.Dentry, opts vfs.OpenOptions) (*vfs.FileDescription, error) {
+	fd, err := kernfs.NewGenericDirectoryFD(rp.Mount(), kd, &d.OrderedChildren, &d.locks, &opts, kernfs.GenericDirectoryFDOptions{
+		SeekEnd: kernfs.SeekEndStaticEntries,
+	})
+	if err != nil {
+		return nil, err
+	}
+	return fd.VFSFileDescription(), nil
+}
+
+// DecRef implements kernfs.Inode.DecRef.
+func (d *dir) DecRef(ctx context.Context) {
+	d.dirRefs.DecRef(func() { d.Destroy(ctx) })
+}
+
+// StatFS implements kernfs.Inode.StatFS.
+func (d *dir) StatFS(ctx context.Context, fs *vfs.Filesystem) (linux.Statfs, error) {
+	return vfs.GenericStatFS(linux.CGROUP_SUPER_MAGIC), nil
+}
+
+// controllerFile represents a generic control file that appears within a cgroup
+// directory.
+//
+// +stateify savable
+type controllerFile struct {
+	kernfs.DynamicBytesFile
+}
+
+func (fs *filesystem) newControllerFile(ctx context.Context, creds *auth.Credentials, data vfs.DynamicBytesSource) kernfs.Inode {
+	f := &controllerFile{}
+	f.Init(ctx, creds, linux.UNNAMED_MAJOR, fs.devMinor, fs.NextIno(), data, readonlyFileMode)
+	return f
+}
+
+func (fs *filesystem) newControllerWritableFile(ctx context.Context, creds *auth.Credentials, data vfs.WritableDynamicBytesSource) kernfs.Inode {
+	f := &controllerFile{}
+	f.Init(ctx, creds, linux.UNNAMED_MAJOR, fs.devMinor, fs.NextIno(), data, writableFileMode)
+	return f
+}
+
+// staticControllerFile represents a generic control file that appears within a
+// cgroup directory which always returns the same data when read.
+// staticControllerFiles are not writable.
+//
+// +stateify savable
+type staticControllerFile struct {
+	kernfs.DynamicBytesFile
+	vfs.StaticData
+}
+
+// Note: We let the caller provide the mode so that static files may be used to
+// fake both readable and writable control files. However, static files are
+// effectively readonly, as attempting to write to them will return EIO
+// regardless of the mode.
+func (fs *filesystem) newStaticControllerFile(ctx context.Context, creds *auth.Credentials, mode linux.FileMode, data string) kernfs.Inode {
+	f := &staticControllerFile{StaticData: vfs.StaticData{Data: data}}
+	f.Init(ctx, creds, linux.UNNAMED_MAJOR, fs.devMinor, fs.NextIno(), f, mode)
+	return f
+}