10 files changed, 220 insertions, 22 deletions

diff --git a/pkg/sentry/kernel/context.go b/pkg/sentry/kernel/context.go
index dd5f0f5fa..bb94769c4 100644
--- a/pkg/sentry/kernel/context.go
+++ b/pkg/sentry/kernel/context.go
@@ -81,7 +81,8 @@ func UTSNamespaceFromContext(ctx context.Context) *UTSNamespace {
 }
 
 // IPCNamespaceFromContext returns the IPC namespace in which ctx is executing,
-// or nil if there is no such IPC namespace.
+// or nil if there is no such IPC namespace. It takes a reference on the
+// namespace.
 func IPCNamespaceFromContext(ctx context.Context) *IPCNamespace {
 	if v := ctx.Value(CtxIPCNamespace); v != nil {
 		return v.(*IPCNamespace)
diff --git a/pkg/sentry/kernel/ipc_namespace.go b/pkg/sentry/kernel/ipc_namespace.go
index 80a070d7e..3f34ee0db 100644
--- a/pkg/sentry/kernel/ipc_namespace.go
+++ b/pkg/sentry/kernel/ipc_namespace.go
@@ -15,6 +15,7 @@
 package kernel
 
 import (
+	"gvisor.dev/gvisor/pkg/context"
 	"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
 	"gvisor.dev/gvisor/pkg/sentry/kernel/semaphore"
 	"gvisor.dev/gvisor/pkg/sentry/kernel/shm"
@@ -24,6 +25,8 @@ import (
 //
 // +stateify savable
 type IPCNamespace struct {
+	IPCNamespaceRefs
+
 	// User namespace which owns this IPC namespace. Immutable.
 	userNS *auth.UserNamespace
 
@@ -33,11 +36,13 @@ type IPCNamespace struct {
 
 // NewIPCNamespace creates a new IPC namespace.
 func NewIPCNamespace(userNS *auth.UserNamespace) *IPCNamespace {
-	return &IPCNamespace{
+	ns := &IPCNamespace{
 		userNS:     userNS,
 		semaphores: semaphore.NewRegistry(userNS),
 		shms:       shm.NewRegistry(userNS),
 	}
+	ns.EnableLeakCheck()
+	return ns
 }
 
 // SemaphoreRegistry returns the semaphore set registry for this namespace.
@@ -50,6 +55,13 @@ func (i *IPCNamespace) ShmRegistry() *shm.Registry {
 	return i.shms
 }
 
+// DecRef implements refs_vfs2.RefCounter.DecRef.
+func (i *IPCNamespace) DecRef(ctx context.Context) {
+	i.IPCNamespaceRefs.DecRef(func() {
+		i.shms.Release(ctx)
+	})
+}
+
 // IPCNamespace returns the task's IPC namespace.
 func (t *Task) IPCNamespace() *IPCNamespace {
 	t.mu.Lock()
diff --git a/pkg/sentry/kernel/ipc_namespace_refs.go b/pkg/sentry/kernel/ipc_namespace_refs.go
new file mode 100644
index 000000000..263919299
--- /dev/null
+++ b/pkg/sentry/kernel/ipc_namespace_refs.go
@@ -0,0 +1,118 @@
+package kernel
+
+import (
+	"fmt"
+	"runtime"
+	"sync/atomic"
+
+	"gvisor.dev/gvisor/pkg/log"
+	refs_vfs1 "gvisor.dev/gvisor/pkg/refs"
+)
+
+// ownerType is used to customize logging. Note that we use a pointer to T so
+// that we do not copy the entire object when passed as a format parameter.
+var IPCNamespaceownerType *IPCNamespace
+
+// Refs implements refs.RefCounter. It keeps a reference count using atomic
+// operations and calls the destructor when the count reaches zero.
+//
+// Note that the number of references is actually refCount + 1 so that a default
+// zero-value Refs object contains one reference.
+//
+// TODO(gvisor.dev/issue/1486): Store stack traces when leak check is enabled in
+// a map with 16-bit hashes, and store the hash in the top 16 bits of refCount.
+// This will allow us to add stack trace information to the leak messages
+// without growing the size of Refs.
+//
+// +stateify savable
+type IPCNamespaceRefs struct {
+	// refCount is composed of two fields:
+	//
+	//	[32-bit speculative references]:[32-bit real references]
+	//
+	// Speculative references are used for TryIncRef, to avoid a CompareAndSwap
+	// loop. See IncRef, DecRef and TryIncRef for details of how these fields are
+	// used.
+	refCount int64
+}
+
+func (r *IPCNamespaceRefs) finalize() {
+	var note string
+	switch refs_vfs1.GetLeakMode() {
+	case refs_vfs1.NoLeakChecking:
+		return
+	case refs_vfs1.UninitializedLeakChecking:
+		note = "(Leak checker uninitialized): "
+	}
+	if n := r.ReadRefs(); n != 0 {
+		log.Warningf("%sRefs %p owned by %T garbage collected with ref count of %d (want 0)", note, r, IPCNamespaceownerType, n)
+	}
+}
+
+// EnableLeakCheck checks for reference leaks when Refs gets garbage collected.
+func (r *IPCNamespaceRefs) EnableLeakCheck() {
+	if refs_vfs1.GetLeakMode() != refs_vfs1.NoLeakChecking {
+		runtime.SetFinalizer(r, (*IPCNamespaceRefs).finalize)
+	}
+}
+
+// ReadRefs returns the current number of references. The returned count is
+// inherently racy and is unsafe to use without external synchronization.
+func (r *IPCNamespaceRefs) ReadRefs() int64 {
+
+	return atomic.LoadInt64(&r.refCount) + 1
+}
+
+// IncRef implements refs.RefCounter.IncRef.
+//
+//go:nosplit
+func (r *IPCNamespaceRefs) IncRef() {
+	if v := atomic.AddInt64(&r.refCount, 1); v <= 0 {
+		panic(fmt.Sprintf("Incrementing non-positive ref count %p owned by %T", r, IPCNamespaceownerType))
+	}
+}
+
+// TryIncRef implements refs.RefCounter.TryIncRef.
+//
+// To do this safely without a loop, a speculative reference is first acquired
+// on the object. This allows multiple concurrent TryIncRef calls to distinguish
+// other TryIncRef calls from genuine references held.
+//
+//go:nosplit
+func (r *IPCNamespaceRefs) TryIncRef() bool {
+	const speculativeRef = 1 << 32
+	v := atomic.AddInt64(&r.refCount, speculativeRef)
+	if int32(v) < 0 {
+
+		atomic.AddInt64(&r.refCount, -speculativeRef)
+		return false
+	}
+
+	atomic.AddInt64(&r.refCount, -speculativeRef+1)
+	return true
+}
+
+// DecRef implements refs.RefCounter.DecRef.
+//
+// Note that speculative references are counted here. Since they were added
+// prior to real references reaching zero, they will successfully convert to
+// real references. In other words, we see speculative references only in the
+// following case:
+//
+//	A: TryIncRef [speculative increase => sees non-negative references]
+//	B: DecRef [real decrease]
+//	A: TryIncRef [transform speculative to real]
+//
+//go:nosplit
+func (r *IPCNamespaceRefs) DecRef(destroy func()) {
+	switch v := atomic.AddInt64(&r.refCount, -1); {
+	case v < -1:
+		panic(fmt.Sprintf("Decrementing non-positive ref count %p, owned by %T", r, IPCNamespaceownerType))
+
+	case v == -1:
+
+		if destroy != nil {
+			destroy()
+		}
+	}
+}
diff --git a/pkg/sentry/kernel/kernel.go b/pkg/sentry/kernel/kernel.go
index 675506269..652cbb732 100644
--- a/pkg/sentry/kernel/kernel.go
+++ b/pkg/sentry/kernel/kernel.go
@@ -828,7 +828,9 @@ func (ctx *createProcessContext) Value(key interface{}) interface{} {
 	case CtxUTSNamespace:
 		return ctx.args.UTSNamespace
 	case CtxIPCNamespace:
-		return ctx.args.IPCNamespace
+		ipcns := ctx.args.IPCNamespace
+		ipcns.IncRef()
+		return ipcns
 	case auth.CtxCredentials:
 		return ctx.args.Credentials
 	case fs.CtxRoot:
@@ -1374,8 +1376,9 @@ func (k *Kernel) RootUTSNamespace() *UTSNamespace {
 	return k.rootUTSNamespace
 }
 
-// RootIPCNamespace returns the root IPCNamespace.
+// RootIPCNamespace takes a reference and returns the root IPCNamespace.
 func (k *Kernel) RootIPCNamespace() *IPCNamespace {
+	k.rootIPCNamespace.IncRef()
 	return k.rootIPCNamespace
 }
 
@@ -1636,7 +1639,9 @@ func (ctx supervisorContext) Value(key interface{}) interface{} {
 	case CtxUTSNamespace:
 		return ctx.k.rootUTSNamespace
 	case CtxIPCNamespace:
-		return ctx.k.rootIPCNamespace
+		ipcns := ctx.k.rootIPCNamespace
+		ipcns.IncRef()
+		return ipcns
 	case auth.CtxCredentials:
 		// The supervisor context is global root.
 		return auth.NewRootCredentials(ctx.k.rootUserNamespace)
diff --git a/pkg/sentry/kernel/kernel_state_autogen.go b/pkg/sentry/kernel/kernel_state_autogen.go
index d8ff396b7..b7d6d4f1c 100644
--- a/pkg/sentry/kernel/kernel_state_autogen.go
+++ b/pkg/sentry/kernel/kernel_state_autogen.go
@@ -242,6 +242,7 @@ func (i *IPCNamespace) StateTypeName() string {
 
 func (i *IPCNamespace) StateFields() []string {
 	return []string{
+		"IPCNamespaceRefs",
 		"userNS",
 		"semaphores",
 		"shms",
@@ -252,17 +253,42 @@ func (i *IPCNamespace) beforeSave() {}
 
 func (i *IPCNamespace) StateSave(stateSinkObject state.Sink) {
 	i.beforeSave()
-	stateSinkObject.Save(0, &i.userNS)
-	stateSinkObject.Save(1, &i.semaphores)
-	stateSinkObject.Save(2, &i.shms)
+	stateSinkObject.Save(0, &i.IPCNamespaceRefs)
+	stateSinkObject.Save(1, &i.userNS)
+	stateSinkObject.Save(2, &i.semaphores)
+	stateSinkObject.Save(3, &i.shms)
 }
 
 func (i *IPCNamespace) afterLoad() {}
 
 func (i *IPCNamespace) StateLoad(stateSourceObject state.Source) {
-	stateSourceObject.Load(0, &i.userNS)
-	stateSourceObject.Load(1, &i.semaphores)
-	stateSourceObject.Load(2, &i.shms)
+	stateSourceObject.Load(0, &i.IPCNamespaceRefs)
+	stateSourceObject.Load(1, &i.userNS)
+	stateSourceObject.Load(2, &i.semaphores)
+	stateSourceObject.Load(3, &i.shms)
+}
+
+func (r *IPCNamespaceRefs) StateTypeName() string {
+	return "pkg/sentry/kernel.IPCNamespaceRefs"
+}
+
+func (r *IPCNamespaceRefs) StateFields() []string {
+	return []string{
+		"refCount",
+	}
+}
+
+func (r *IPCNamespaceRefs) beforeSave() {}
+
+func (r *IPCNamespaceRefs) StateSave(stateSinkObject state.Sink) {
+	r.beforeSave()
+	stateSinkObject.Save(0, &r.refCount)
+}
+
+func (r *IPCNamespaceRefs) afterLoad() {}
+
+func (r *IPCNamespaceRefs) StateLoad(stateSourceObject state.Source) {
+	stateSourceObject.Load(0, &r.refCount)
 }
 
 func (k *Kernel) StateTypeName() string {
@@ -2292,6 +2318,7 @@ func init() {
 	state.Register((*FSContext)(nil))
 	state.Register((*FSContextRefs)(nil))
 	state.Register((*IPCNamespace)(nil))
+	state.Register((*IPCNamespaceRefs)(nil))
 	state.Register((*Kernel)(nil))
 	state.Register((*SocketRecord)(nil))
 	state.Register((*SocketRecordVFS1)(nil))
diff --git a/pkg/sentry/kernel/shm/shm.go b/pkg/sentry/kernel/shm/shm.go
index 00c03585e..ebbebf46b 100644
--- a/pkg/sentry/kernel/shm/shm.go
+++ b/pkg/sentry/kernel/shm/shm.go
@@ -321,9 +321,32 @@ func (r *Registry) remove(s *Shm) {
 	r.totalPages -= s.effectiveSize / usermem.PageSize
 }
 
+// Release drops the self-reference of each active shm segment in the registry.
+// It is called when the kernel.IPCNamespace containing r is being destroyed.
+func (r *Registry) Release(ctx context.Context) {
+	// Because Shm.DecRef() may acquire the same locks, collect the segments to
+	// release first. Note that this should not race with any updates to r, since
+	// the IPC namespace containing it has no more references.
+	toRelease := make([]*Shm, 0)
+	r.mu.Lock()
+	for _, s := range r.keysToShms {
+		s.mu.Lock()
+		if !s.pendingDestruction {
+			toRelease = append(toRelease, s)
+		}
+		s.mu.Unlock()
+	}
+	r.mu.Unlock()
+
+	for _, s := range toRelease {
+		r.dissociateKey(s)
+		s.DecRef(ctx)
+	}
+}
+
 // Shm represents a single shared memory segment.
 //
-// Shm segment are backed directly by an allocation from platform memory.
+// Shm segments are backed directly by an allocation from platform memory.
 // Segments are always mapped as a whole, greatly simplifying how mappings are
 // tracked. However note that mremap and munmap calls may cause the vma for a
 // segment to become fragmented; which requires special care when unmapping a
@@ -652,17 +675,20 @@ func (s *Shm) MarkDestroyed(ctx context.Context) {
 	s.registry.dissociateKey(s)
 
 	s.mu.Lock()
-	defer s.mu.Unlock()
-	if !s.pendingDestruction {
-		s.pendingDestruction = true
-		// Drop the self-reference so destruction occurs when all
-		// external references are gone.
-		//
-		// N.B. This cannot be the final DecRef, as the caller also
-		// holds a reference.
-		s.DecRef(ctx)
+	if s.pendingDestruction {
+		s.mu.Unlock()
 		return
 	}
+	s.pendingDestruction = true
+	s.mu.Unlock()
+
+	// Drop the self-reference so destruction occurs when all
+	// external references are gone.
+	//
+	// N.B. This cannot be the final DecRef, as the caller also
+	// holds a reference.
+	s.DecRef(ctx)
+	return
 }
 
 // checkOwnership verifies whether a segment may be accessed by ctx as an
diff --git a/pkg/sentry/kernel/task.go b/pkg/sentry/kernel/task.go
index e90a19cfb..037971393 100644
--- a/pkg/sentry/kernel/task.go
+++ b/pkg/sentry/kernel/task.go
@@ -656,7 +656,9 @@ func (t *Task) Value(key interface{}) interface{} {
 	case CtxUTSNamespace:
 		return t.utsns
 	case CtxIPCNamespace:
-		return t.ipcns
+		ipcns := t.IPCNamespace()
+		ipcns.IncRef()
+		return ipcns
 	case CtxTask:
 		return t
 	case auth.CtxCredentials:
diff --git a/pkg/sentry/kernel/task_clone.go b/pkg/sentry/kernel/task_clone.go
index fce1064a7..7a053f369 100644
--- a/pkg/sentry/kernel/task_clone.go
+++ b/pkg/sentry/kernel/task_clone.go
@@ -203,6 +203,8 @@ func (t *Task) Clone(opts *CloneOptions) (ThreadID, *SyscallControl, error) {
 		// Note that "If CLONE_NEWIPC is set, then create the process in a new IPC
 		// namespace"
 		ipcns = NewIPCNamespace(userns)
+	} else {
+		ipcns.IncRef()
 	}
 
 	netns := t.NetworkNamespace()
@@ -218,6 +220,7 @@ func (t *Task) Clone(opts *CloneOptions) (ThreadID, *SyscallControl, error) {
 
 	tc, err := t.tc.Fork(t, t.k, !opts.NewAddressSpace)
 	if err != nil {
+		ipcns.DecRef(t)
 		return 0, nil, err
 	}
 	// clone() returns 0 in the child.
@@ -227,6 +230,7 @@ func (t *Task) Clone(opts *CloneOptions) (ThreadID, *SyscallControl, error) {
 	}
 	if opts.SetTLS {
 		if !tc.Arch.SetTLS(uintptr(opts.TLS)) {
+			ipcns.DecRef(t)
 			return 0, nil, syserror.EPERM
 		}
 	}
@@ -509,6 +513,7 @@ func (t *Task) Unshare(opts *SharingOptions) error {
 		}
 		// Note that "If CLONE_NEWIPC is set, then create the process in a new IPC
 		// namespace"
+		t.ipcns.DecRef(t)
 		t.ipcns = NewIPCNamespace(creds.UserNamespace)
 	}
 	var oldFDTable *FDTable
diff --git a/pkg/sentry/kernel/task_exit.go b/pkg/sentry/kernel/task_exit.go
index b400a8b41..239551eb6 100644
--- a/pkg/sentry/kernel/task_exit.go
+++ b/pkg/sentry/kernel/task_exit.go
@@ -280,6 +280,7 @@ func (*runExitMain) execute(t *Task) taskRunState {
 		t.mountNamespaceVFS2.DecRef(t)
 		t.mountNamespaceVFS2 = nil
 	}
+	t.ipcns.DecRef(t)
 	t.mu.Unlock()
 
 	// If this is the last task to exit from the thread group, release the
diff --git a/pkg/sentry/kernel/task_start.go b/pkg/sentry/kernel/task_start.go
index 64c1e120a..6e2ff573a 100644
--- a/pkg/sentry/kernel/task_start.go
+++ b/pkg/sentry/kernel/task_start.go
@@ -104,6 +104,7 @@ func (ts *TaskSet) NewTask(cfg *TaskConfig) (*Task, error) {
 		cfg.TaskContext.release()
 		cfg.FSContext.DecRef(t)
 		cfg.FDTable.DecRef(t)
+		cfg.IPCNamespace.DecRef(t)
 		if cfg.MountNamespaceVFS2 != nil {
 			cfg.MountNamespaceVFS2.DecRef(t)
 		}