Check for misuse of kernel.Task as context.Context.

Checks in Task.block() and Task.Value() are conditional on race detection being
enabled, since these functions are relatively hot. Checks in Task.SleepStart()
and Task.UninterruptibleSleepStart() are enabled unconditionally, since these
functions are not thought to lie on any critical paths, and misuse of these
functions is required for b/168241471 to manifest.

PiperOrigin-RevId: 342342175

1 files changed, 189 insertions, 0 deletions

diff --git a/pkg/sentry/kernel/task_context.go b/pkg/sentry/kernel/task_context.go
new file mode 100644
index 000000000..70b0699dc
--- /dev/null
+++ b/pkg/sentry/kernel/task_context.go
@@ -0,0 +1,189 @@
+// 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 kernel
+
+import (
+	"time"
+
+	"gvisor.dev/gvisor/pkg/context"
+	"gvisor.dev/gvisor/pkg/log"
+	"gvisor.dev/gvisor/pkg/sentry/fs"
+	"gvisor.dev/gvisor/pkg/sentry/inet"
+	"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
+	ktime "gvisor.dev/gvisor/pkg/sentry/kernel/time"
+	"gvisor.dev/gvisor/pkg/sentry/limits"
+	"gvisor.dev/gvisor/pkg/sentry/pgalloc"
+	"gvisor.dev/gvisor/pkg/sentry/platform"
+	"gvisor.dev/gvisor/pkg/sentry/unimpl"
+	"gvisor.dev/gvisor/pkg/sentry/uniqueid"
+	"gvisor.dev/gvisor/pkg/sentry/vfs"
+	"gvisor.dev/gvisor/pkg/sync"
+)
+
+// Deadline implements context.Context.Deadline.
+func (t *Task) Deadline() (time.Time, bool) {
+	return time.Time{}, false
+}
+
+// Done implements context.Context.Done.
+func (t *Task) Done() <-chan struct{} {
+	return nil
+}
+
+// Err implements context.Context.Err.
+func (t *Task) Err() error {
+	return nil
+}
+
+// Value implements context.Context.Value.
+//
+// Preconditions: The caller must be running on the task goroutine.
+func (t *Task) Value(key interface{}) interface{} {
+	// This function is very hot; skip this check outside of +race builds.
+	if sync.RaceEnabled {
+		t.assertTaskGoroutine()
+	}
+	return t.contextValue(key, true /* isTaskGoroutine */)
+}
+
+func (t *Task) contextValue(key interface{}, isTaskGoroutine bool) interface{} {
+	switch key {
+	case CtxCanTrace:
+		return t.CanTrace
+	case CtxKernel:
+		return t.k
+	case CtxPIDNamespace:
+		return t.tg.pidns
+	case CtxUTSNamespace:
+		if !isTaskGoroutine {
+			t.mu.Lock()
+			defer t.mu.Unlock()
+		}
+		return t.utsns
+	case CtxIPCNamespace:
+		if !isTaskGoroutine {
+			t.mu.Lock()
+			defer t.mu.Unlock()
+		}
+		ipcns := t.ipcns
+		ipcns.IncRef()
+		return ipcns
+	case CtxTask:
+		return t
+	case auth.CtxCredentials:
+		return t.creds.Load()
+	case context.CtxThreadGroupID:
+		return int32(t.tg.ID())
+	case fs.CtxRoot:
+		if !isTaskGoroutine {
+			t.mu.Lock()
+			defer t.mu.Unlock()
+		}
+		return t.fsContext.RootDirectory()
+	case vfs.CtxRoot:
+		if !isTaskGoroutine {
+			t.mu.Lock()
+			defer t.mu.Unlock()
+		}
+		return t.fsContext.RootDirectoryVFS2()
+	case vfs.CtxMountNamespace:
+		if !isTaskGoroutine {
+			t.mu.Lock()
+			defer t.mu.Unlock()
+		}
+		t.mountNamespaceVFS2.IncRef()
+		return t.mountNamespaceVFS2
+	case fs.CtxDirentCacheLimiter:
+		return t.k.DirentCacheLimiter
+	case inet.CtxStack:
+		return t.NetworkContext()
+	case ktime.CtxRealtimeClock:
+		return t.k.RealtimeClock()
+	case limits.CtxLimits:
+		return t.tg.limits
+	case pgalloc.CtxMemoryFile:
+		return t.k.mf
+	case pgalloc.CtxMemoryFileProvider:
+		return t.k
+	case platform.CtxPlatform:
+		return t.k
+	case uniqueid.CtxGlobalUniqueID:
+		return t.k.UniqueID()
+	case uniqueid.CtxGlobalUniqueIDProvider:
+		return t.k
+	case uniqueid.CtxInotifyCookie:
+		return t.k.GenerateInotifyCookie()
+	case unimpl.CtxEvents:
+		return t.k
+	default:
+		return nil
+	}
+}
+
+// taskAsyncContext implements context.Context for a goroutine that performs
+// work on behalf of a Task, but is not the task goroutine.
+type taskAsyncContext struct {
+	context.NoopSleeper
+
+	t *Task
+}
+
+// AsyncContext returns a context.Context representing t. The returned
+// context.Context is intended for use by goroutines other than t's task
+// goroutine; for example, signal delivery to t will not interrupt goroutines
+// that are blocking using the returned context.Context.
+func (t *Task) AsyncContext() context.Context {
+	return taskAsyncContext{t: t}
+}
+
+// Debugf implements log.Logger.Debugf.
+func (ctx taskAsyncContext) Debugf(format string, v ...interface{}) {
+	ctx.t.Debugf(format, v...)
+}
+
+// Infof implements log.Logger.Infof.
+func (ctx taskAsyncContext) Infof(format string, v ...interface{}) {
+	ctx.t.Infof(format, v...)
+}
+
+// Warningf implements log.Logger.Warningf.
+func (ctx taskAsyncContext) Warningf(format string, v ...interface{}) {
+	ctx.t.Warningf(format, v...)
+}
+
+// IsLogging implements log.Logger.IsLogging.
+func (ctx taskAsyncContext) IsLogging(level log.Level) bool {
+	return ctx.t.IsLogging(level)
+}
+
+// Deadline implements context.Context.Deadline.
+func (ctx taskAsyncContext) Deadline() (time.Time, bool) {
+	return time.Time{}, false
+}
+
+// Done implements context.Context.Done.
+func (ctx taskAsyncContext) Done() <-chan struct{} {
+	return nil
+}
+
+// Err implements context.Context.Err.
+func (ctx taskAsyncContext) Err() error {
+	return nil
+}
+
+// Value implements context.Context.Value.
+func (ctx taskAsyncContext) Value(key interface{}) interface{} {
+	return ctx.t.contextValue(key, false /* isTaskGoroutine */)
+}