Create ipc.Registry.

Create ipc.Registry to hold fields, and define functionality common to
all SysV registries, and have registries use it.

8 files changed, 378 insertions, 204 deletions

diff --git a/pkg/sentry/kernel/ipc/BUILD b/pkg/sentry/kernel/ipc/BUILD
index 14f73ee17..e42a94e15 100644
--- a/pkg/sentry/kernel/ipc/BUILD
+++ b/pkg/sentry/kernel/ipc/BUILD
@@ -6,10 +6,14 @@ go_library(
     name = "ipc",
     srcs = [
         "object.go",
+        "registry.go",
     ],
     visibility = ["//pkg/sentry:internal"],
     deps = [
         "//pkg/abi/linux",
+        "//pkg/context",
+        "//pkg/errors/linuxerr",
+        "//pkg/log",
         "//pkg/sentry/fs",
         "//pkg/sentry/kernel/auth",
     ],
diff --git a/pkg/sentry/kernel/ipc/object.go b/pkg/sentry/kernel/ipc/object.go
index 769ff44e1..387b35e7e 100644
--- a/pkg/sentry/kernel/ipc/object.go
+++ b/pkg/sentry/kernel/ipc/object.go
@@ -13,6 +13,8 @@
 // limitations under the License.
 
 // Package ipc defines functionality and utilities common to sysvipc mechanisms.
+//
+// Lock ordering: [shm/semaphore/msgqueue].Registry.mu -> Mechanism
 package ipc
 
 import (
@@ -29,6 +31,8 @@ type ID int32
 
 // Object represents an abstract IPC object with fields common to all IPC
 // mechanisms.
+//
+// +stateify savable
 type Object struct {
 	// User namespace which owns the IPC namespace which owns the IPC object.
 	// Immutable.
@@ -54,22 +58,26 @@ type Object struct {
 // be looked at as a container for an ipc.Object, which is by definition a fully
 // functional SysV object.
 type Mechanism interface {
-	// Object returns a pointer to the mechanism's ipc.Object. Mechanism.Lock,
-	// and Mechanism.Unlock should be used when the object is used.
-	Object() *Object
-
 	// Lock behaves the same as Mutex.Lock on the mechanism.
 	Lock()
 
 	// Unlock behaves the same as Mutex.Unlock on the mechanism.
 	Unlock()
+
+	// Object returns a pointer to the mechanism's ipc.Object. Mechanism.Lock,
+	// and Mechanism.Unlock should be used when the object is used.
+	Object() *Object
+
+	// Destroy destroys the mechanism.
+	Destroy()
 }
 
-// NewObject returns a new, initialized ipc.Object.
-func NewObject(un *auth.UserNamespace, id ID, key Key, creator, owner fs.FileOwner, perms fs.FilePermissions) *Object {
+// NewObject returns a new, initialized ipc.Object. The newly returned object
+// doesn't have a valid ID. When the object is registered, the registry assigns
+// it a new unique ID.
+func NewObject(un *auth.UserNamespace, key Key, creator, owner fs.FileOwner, perms fs.FilePermissions) *Object {
 	return &Object{
 		UserNS:  un,
-		ID:      id,
 		Key:     key,
 		Creator: creator,
 		Owner:   owner,
diff --git a/pkg/sentry/kernel/ipc/registry.go b/pkg/sentry/kernel/ipc/registry.go
new file mode 100644
index 000000000..91de19070
--- /dev/null
+++ b/pkg/sentry/kernel/ipc/registry.go
@@ -0,0 +1,196 @@
+// 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 ipc
+
+import (
+	"gvisor.dev/gvisor/pkg/abi/linux"
+	"gvisor.dev/gvisor/pkg/context"
+	"gvisor.dev/gvisor/pkg/errors/linuxerr"
+	"gvisor.dev/gvisor/pkg/log"
+	"gvisor.dev/gvisor/pkg/sentry/fs"
+	"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
+)
+
+// Registry is similar to Object, but for registries. It represent an abstract
+// SysV IPC registry with fields common to all SysV registries. Registry is not
+// thread-safe, and should be protected using a mutex.
+//
+// +stateify savable
+type Registry struct {
+	// UserNS owning the IPC namespace this registry belongs to. Immutable.
+	UserNS *auth.UserNamespace
+
+	// objects is a map of IDs to IPC mechanisms.
+	objects map[ID]Mechanism
+
+	// KeysToIDs maps a lookup key to an ID.
+	keysToIDs map[Key]ID
+
+	// lastIDUsed is used to find the next available ID for object creation.
+	lastIDUsed ID
+}
+
+// NewRegistry return a new, initialized ipc.Registry.
+func NewRegistry(userNS *auth.UserNamespace) *Registry {
+	return &Registry{
+		UserNS:    userNS,
+		objects:   make(map[ID]Mechanism),
+		keysToIDs: make(map[Key]ID),
+	}
+}
+
+// Find uses key to search for and return a SysV mechanism. Find returns an
+// error if an object is found by shouldn't be, or if the user doesn't have
+// permission to use the object. If no object is found, Find checks create
+// flag, and returns an error only if it's false.
+func (r *Registry) Find(ctx context.Context, key Key, mode linux.FileMode, create, exclusive bool) (Mechanism, error) {
+	if id, ok := r.keysToIDs[key]; ok {
+		mech := r.objects[id]
+		mech.Lock()
+		defer mech.Unlock()
+
+		obj := mech.Object()
+		creds := auth.CredentialsFromContext(ctx)
+		if !obj.CheckPermissions(creds, fs.PermsFromMode(mode)) {
+			// The [calling process / user] does not have permission to access
+			// the set, and does not have the CAP_IPC_OWNER capability in the
+			// user namespace that governs its IPC namespace.
+			return nil, linuxerr.EACCES
+		}
+
+		if create && exclusive {
+			// IPC_CREAT and IPC_EXCL were specified, but an object already
+			// exists for key.
+			return nil, linuxerr.EEXIST
+		}
+		return mech, nil
+	}
+
+	if !create {
+		// No object exists for key and msgflg did not specify IPC_CREAT.
+		return nil, linuxerr.ENOENT
+	}
+
+	return nil, nil
+}
+
+// Register adds the given object into Registry.Objects, and assigns it a new
+// ID. It returns an error if all IDs are exhausted.
+func (r *Registry) Register(m Mechanism) error {
+	id, err := r.newID()
+	if err != nil {
+		return err
+	}
+
+	obj := m.Object()
+	obj.ID = id
+
+	r.objects[id] = m
+	r.keysToIDs[obj.Key] = id
+
+	return nil
+}
+
+// newID finds the first unused ID in the registry, and returns an error if
+// non is found.
+func (r *Registry) newID() (ID, error) {
+	// Find the next available ID.
+	for id := r.lastIDUsed + 1; id != r.lastIDUsed; id++ {
+		// Handle wrap around.
+		if id < 0 {
+			id = 0
+			continue
+		}
+		if r.objects[id] == nil {
+			r.lastIDUsed = id
+			return id, nil
+		}
+	}
+
+	log.Warningf("ids exhausted, they may be leaking")
+
+	// The man pages for shmget(2) mention that ENOSPC should be used if "All
+	// possible shared memory IDs have been taken (SHMMNI)". Other SysV
+	// mechanisms don't have a specific errno for running out of IDs, but they
+	// return ENOSPC if the max number of objects is exceeded, so we assume that
+	// it's the same case.
+	return 0, linuxerr.ENOSPC
+}
+
+// Remove removes the mechanism with the given id from the registry, and calls
+// mechanism.Destroy to perform mechanism-specific removal.
+func (r *Registry) Remove(id ID, creds *auth.Credentials) error {
+	mech := r.objects[id]
+	if mech == nil {
+		return linuxerr.EINVAL
+	}
+
+	mech.Lock()
+	defer mech.Unlock()
+
+	obj := mech.Object()
+
+	// The effective user ID of the calling process must match the creator or
+	// owner of the [mechanism], or the caller must be privileged.
+	if !obj.CheckOwnership(creds) {
+		return linuxerr.EPERM
+	}
+
+	delete(r.objects, obj.ID)
+	delete(r.keysToIDs, obj.Key)
+	mech.Destroy()
+
+	return nil
+}
+
+// ForAllObjects executes a given function for all given objects.
+func (r *Registry) ForAllObjects(f func(o Mechanism)) {
+	for _, o := range r.objects {
+		f(o)
+	}
+}
+
+// FindByID returns the mechanism with the given ID, nil if non exists.
+func (r *Registry) FindByID(id ID) Mechanism {
+	return r.objects[id]
+}
+
+// DissociateKey removes the association between a mechanism and its key
+// (deletes it from r.keysToIDs), preventing it from being discovered by any new
+// process, but not necessarily destroying it. If the given key doesn't exist,
+// nothing is changed.
+func (r *Registry) DissociateKey(key Key) {
+	delete(r.keysToIDs, key)
+}
+
+// DissociateID removes the association between a mechanism and its ID (deletes
+// it from r.objects). An ID can't be removed unless the associated key is
+// removed already, this is done to prevent the users from acquiring nil a
+// Mechanism.
+//
+// Precondition: must be preceded by a call to r.DissociateKey.
+func (r *Registry) DissociateID(id ID) {
+	delete(r.objects, id)
+}
+
+// ObjectCount returns the number of registered objects.
+func (r *Registry) ObjectCount() int {
+	return len(r.objects)
+}
+
+// LastIDUsed returns the last used ID.
+func (r *Registry) LastIDUsed() ID {
+	return r.lastIDUsed
+}
diff --git a/pkg/sentry/kernel/semaphore/BUILD b/pkg/sentry/kernel/semaphore/BUILD
index 5dd607953..2ae08ed12 100644
--- a/pkg/sentry/kernel/semaphore/BUILD
+++ b/pkg/sentry/kernel/semaphore/BUILD
@@ -26,7 +26,6 @@ go_library(
         "//pkg/abi/linux",
         "//pkg/context",
         "//pkg/errors/linuxerr",
-        "//pkg/log",
         "//pkg/sentry/fs",
         "//pkg/sentry/kernel/auth",
         "//pkg/sentry/kernel/ipc",
@@ -42,10 +41,11 @@ go_test(
     srcs = ["semaphore_test.go"],
     library = ":semaphore",
     deps = [
-        "//pkg/abi/linux",
-        "//pkg/context",
-        "//pkg/sentry/contexttest",
-        "//pkg/sentry/kernel/auth",
-        "//pkg/syserror",
+        "//pkg/abi/linux",  # keep
+        "//pkg/context",  # keep
+        "//pkg/sentry/contexttest",  # keep
+        "//pkg/sentry/kernel/auth",  # keep
+        "//pkg/sentry/kernel/ipc",  # keep
+        "//pkg/syserror",  # keep
     ],
 )
diff --git a/pkg/sentry/kernel/semaphore/semaphore.go b/pkg/sentry/kernel/semaphore/semaphore.go
index d609d88e2..b7879d284 100644
--- a/pkg/sentry/kernel/semaphore/semaphore.go
+++ b/pkg/sentry/kernel/semaphore/semaphore.go
@@ -21,7 +21,6 @@ import (
 	"gvisor.dev/gvisor/pkg/abi/linux"
 	"gvisor.dev/gvisor/pkg/context"
 	"gvisor.dev/gvisor/pkg/errors/linuxerr"
-	"gvisor.dev/gvisor/pkg/log"
 	"gvisor.dev/gvisor/pkg/sentry/fs"
 	"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
 	"gvisor.dev/gvisor/pkg/sentry/kernel/ipc"
@@ -48,12 +47,12 @@ const (
 //
 // +stateify savable
 type Registry struct {
-	// userNS owning the ipc name this registry belongs to. Immutable.
-	userNS *auth.UserNamespace
 	// mu protects all fields below.
-	mu         sync.Mutex `state:"nosave"`
-	semaphores map[ipc.ID]*Set
-	lastIDUsed ipc.ID
+	mu sync.Mutex `state:"nosave"`
+
+	// reg defines basic fields and operations needed for all SysV registries.
+	reg *ipc.Registry
+
 	// indexes maintains a mapping between a set's index in virtual array and
 	// its identifier.
 	indexes map[int32]ipc.ID
@@ -69,7 +68,6 @@ type Set struct {
 	// mu protects all fields below.
 	mu sync.Mutex `state:"nosave"`
 
-	// obj defines basic fields that should be included in all SysV IPC objects.
 	obj *ipc.Object
 
 	opTime     ktime.Time
@@ -109,9 +107,8 @@ type waiter struct {
 // NewRegistry creates a new semaphore set registry.
 func NewRegistry(userNS *auth.UserNamespace) *Registry {
 	return &Registry{
-		userNS:     userNS,
-		semaphores: make(map[ipc.ID]*Set),
-		indexes:    make(map[int32]ipc.ID),
+		reg:     ipc.NewRegistry(userNS),
+		indexes: make(map[int32]ipc.ID),
 	}
 }
 
@@ -129,31 +126,19 @@ func (r *Registry) FindOrCreate(ctx context.Context, key ipc.Key, nsems int32, m
 	defer r.mu.Unlock()
 
 	if !private {
-		// Look up an existing semaphore.
-		if set := r.findByKey(key); set != nil {
-			set.mu.Lock()
-			defer set.mu.Unlock()
-
-			// Check that caller can access semaphore set.
-			creds := auth.CredentialsFromContext(ctx)
-			if !set.obj.CheckPermissions(creds, fs.PermsFromMode(mode)) {
-				return nil, linuxerr.EACCES
-			}
+		set, err := r.reg.Find(ctx, key, mode, create, exclusive)
+		if err != nil {
+			return nil, err
+		}
 
-			// Validate parameters.
+		// Validate semaphore-specific parameters.
+		if set != nil {
+			set := set.(*Set)
 			if nsems > int32(set.Size()) {
 				return nil, linuxerr.EINVAL
 			}
-			if create && exclusive {
-				return nil, linuxerr.EEXIST
-			}
 			return set, nil
 		}
-
-		if !create {
-			// Semaphore not found and should not be created.
-			return nil, syserror.ENOENT
-		}
 	}
 
 	// Zero is only valid if an existing set is found.
@@ -163,9 +148,9 @@ func (r *Registry) FindOrCreate(ctx context.Context, key ipc.Key, nsems int32, m
 
 	// Apply system limits.
 	//
-	// Map semaphores and map indexes in a registry are of the same size,
-	// check map semaphores only here for the system limit.
-	if len(r.semaphores) >= setsMax {
+	// Map reg.objects and map indexes in a registry are of the same size,
+	// check map reg.objects only here for the system limit.
+	if r.reg.ObjectCount() >= setsMax {
 		return nil, syserror.ENOSPC
 	}
 	if r.totalSems() > int(semsTotalMax-nsems) {
@@ -173,9 +158,7 @@ func (r *Registry) FindOrCreate(ctx context.Context, key ipc.Key, nsems int32, m
 	}
 
 	// Finally create a new set.
-	owner := fs.FileOwnerFromContext(ctx)
-	perms := fs.FilePermsFromMode(mode)
-	return r.newSet(ctx, key, owner, owner, perms, nsems)
+	return r.newSetLocked(ctx, key, fs.FileOwnerFromContext(ctx), fs.FilePermsFromMode(mode), nsems)
 }
 
 // IPCInfo returns information about system-wide semaphore limits and parameters.
@@ -202,7 +185,7 @@ func (r *Registry) SemInfo() *linux.SemInfo {
 	defer r.mu.Unlock()
 
 	info := r.IPCInfo()
-	info.SemUsz = uint32(len(r.semaphores))
+	info.SemUsz = uint32(r.reg.ObjectCount())
 	info.SemAem = uint32(r.totalSems())
 
 	return info
@@ -225,74 +208,59 @@ func (r *Registry) HighestIndex() int32 {
 	return highestIndex
 }
 
-// RemoveID removes set with give 'id' from the registry and marks the set as
+// Remove removes set with give 'id' from the registry and marks the set as
 // dead. All waiters will be awakened and fail.
-func (r *Registry) RemoveID(id ipc.ID, creds *auth.Credentials) error {
+func (r *Registry) Remove(id ipc.ID, creds *auth.Credentials) error {
 	r.mu.Lock()
 	defer r.mu.Unlock()
 
-	set := r.semaphores[id]
-	if set == nil {
-		return linuxerr.EINVAL
-	}
+	r.reg.Remove(id, creds)
+
 	index, found := r.findIndexByID(id)
 	if !found {
 		// Inconsistent state.
 		panic(fmt.Sprintf("unable to find an index for ID: %d", id))
 	}
-
-	set.mu.Lock()
-	defer set.mu.Unlock()
-
-	// "The effective user ID of the calling process must match the creator or
-	// owner of the semaphore set, or the caller must be privileged."
-	if !set.obj.CheckOwnership(creds) {
-		return linuxerr.EACCES
-	}
-
-	delete(r.semaphores, set.obj.ID)
 	delete(r.indexes, index)
-	set.destroy()
+
 	return nil
 }
 
-func (r *Registry) newSet(ctx context.Context, key ipc.Key, owner, creator fs.FileOwner, perms fs.FilePermissions, nsems int32) (*Set, error) {
-	// Find the next available ID.
-	for id := r.lastIDUsed + 1; id != r.lastIDUsed; id++ {
-		// Handle wrap around.
-		if id < 0 {
-			id = 0
-			continue
-		}
-		if r.semaphores[id] == nil {
-			index, found := r.findFirstAvailableIndex()
-			if !found {
-				panic("unable to find an available index")
-			}
-			r.indexes[index] = id
-			r.lastIDUsed = id
-
-			set := &Set{
-				registry:   r,
-				obj:        ipc.NewObject(r.userNS, ipc.ID(id), ipc.Key(key), creator, owner, perms),
-				changeTime: ktime.NowFromContext(ctx),
-				sems:       make([]sem, nsems),
-			}
-			r.semaphores[id] = set
+// newSetLocked creates a new Set using given fields. An error is returned if there
+// are no more available identifiers.
+//
+// Precondition: r.mu must be held.
+func (r *Registry) newSetLocked(ctx context.Context, key ipc.Key, creator fs.FileOwner, perms fs.FilePermissions, nsems int32) (*Set, error) {
+	set := &Set{
+		registry:   r,
+		obj:        ipc.NewObject(r.reg.UserNS, ipc.Key(key), creator, creator, perms),
+		changeTime: ktime.NowFromContext(ctx),
+		sems:       make([]sem, nsems),
+	}
 
-			return set, nil
-		}
+	err := r.reg.Register(set)
+	if err != nil {
+		return nil, err
+	}
+
+	index, found := r.findFirstAvailableIndex()
+	if !found {
+		panic("unable to find an available index")
 	}
+	r.indexes[index] = set.obj.ID
 
-	log.Warningf("Semaphore map is full, they must be leaking")
-	return nil, syserror.ENOMEM
+	return set, nil
 }
 
 // FindByID looks up a set given an ID.
 func (r *Registry) FindByID(id ipc.ID) *Set {
 	r.mu.Lock()
 	defer r.mu.Unlock()
-	return r.semaphores[id]
+	mech := r.reg.FindByID(id)
+	if mech == nil {
+		return nil
+	}
+	return mech.(*Set)
 }
 
 // FindByIndex looks up a set given an index.
@@ -304,16 +272,7 @@ func (r *Registry) FindByIndex(index int32) *Set {
 	if !present {
 		return nil
 	}
-	return r.semaphores[id]
-}
-
-func (r *Registry) findByKey(key ipc.Key) *Set {
-	for _, v := range r.semaphores {
-		if v.obj.Key == key {
-			return v
-		}
-	}
-	return nil
+	return r.reg.FindByID(id).(*Set)
 }
 
 func (r *Registry) findIndexByID(id ipc.ID) (int32, bool) {
@@ -336,9 +295,11 @@ func (r *Registry) findFirstAvailableIndex() (int32, bool) {
 
 func (r *Registry) totalSems() int {
 	totalSems := 0
-	for _, v := range r.semaphores {
-		totalSems += v.Size()
-	}
+	r.reg.ForAllObjects(
+		func(o ipc.Mechanism) {
+			totalSems += o.(*Set).Size()
+		},
+	)
 	return totalSems
 }
 
@@ -347,6 +308,23 @@ func (s *Set) ID() ipc.ID {
 	return s.obj.ID
 }
 
+// Object implements ipc.Mechanism.Object.
+func (s *Set) Object() *ipc.Object {
+	return s.obj
+}
+
+// Lock implements ipc.Mechanism.Lock.
+func (s *Set) Lock() {
+	s.mu.Lock()
+}
+
+// Unlock implements ipc.mechanism.Unlock.
+//
+// +checklocksignore
+func (s *Set) Unlock() {
+	s.mu.Unlock()
+}
+
 func (s *Set) findSem(num int32) *sem {
 	if num < 0 || int(num) >= s.Size() {
 		return nil
@@ -671,10 +649,10 @@ func (s *Set) AbortWait(num int32, ch chan struct{}) {
 	// Waiter may not be found in case it raced with wakeWaiters().
 }
 
-// destroy destroys the set.
+// Destroy implements ipc.Mechanism.Destroy.
 //
 // Preconditions: Caller must hold 's.mu'.
-func (s *Set) destroy() {
+func (s *Set) Destroy() {
 	// Notify all waiters. They will fail on the next attempt to execute
 	// operations and return error.
 	s.dead = true
diff --git a/pkg/sentry/kernel/semaphore/semaphore_test.go b/pkg/sentry/kernel/semaphore/semaphore_test.go
index 0c7abb68e..2e4ab8121 100644
--- a/pkg/sentry/kernel/semaphore/semaphore_test.go
+++ b/pkg/sentry/kernel/semaphore/semaphore_test.go
@@ -139,6 +139,7 @@ func TestUnregister(t *testing.T) {
 	ctx := contexttest.Context(t)
 	r := NewRegistry(auth.NewRootUserNamespace())
 	set, err := r.FindOrCreate(ctx, 123, 2, linux.FileMode(0x600), true, true, true)
+
 	if err != nil {
 		t.Fatalf("FindOrCreate() failed, err: %v", err)
 	}
@@ -156,8 +157,8 @@ func TestUnregister(t *testing.T) {
 	}
 
 	creds := auth.CredentialsFromContext(ctx)
-	if err := r.RemoveID(set.obj.ID, creds); err != nil {
-		t.Fatalf("RemoveID(%d) failed, err: %v", set.obj.ID, err)
+	if err := r.Remove(set.obj.ID, creds); err != nil {
+		t.Fatalf("Remove(%d) failed, err: %v", set.obj.ID, err)
 	}
 	if !set.dead {
 		t.Fatalf("set is not dead: %+v", set)
diff --git a/pkg/sentry/kernel/shm/shm.go b/pkg/sentry/kernel/shm/shm.go
index 459ae8c30..2abf467d7 100644
--- a/pkg/sentry/kernel/shm/shm.go
+++ b/pkg/sentry/kernel/shm/shm.go
@@ -64,38 +64,34 @@ type Registry struct {
 	// mu protects all fields below.
 	mu sync.Mutex `state:"nosave"`
 
-	// shms maps segment ids to segments.
+	// reg defines basic fields and operations needed for all SysV registries.
 	//
-	// shms holds all referenced segments, which are removed on the last
+	// Withing reg, there are two maps, Objects and KeysToIDs.
+	//
+	// reg.objects holds all referenced segments, which are removed on the last
 	// DecRef. Thus, it cannot itself hold a reference on the Shm.
 	//
 	// Since removal only occurs after the last (unlocked) DecRef, there
 	// exists a short window during which a Shm still exists in Shm, but is
 	// unreferenced. Users must use TryIncRef to determine if the Shm is
 	// still valid.
-	shms map[ipc.ID]*Shm
-
-	// keysToShms maps segment keys to segments.
 	//
-	// Shms in keysToShms are guaranteed to be referenced, as they are
+	// keysToIDs maps segment keys to IDs.
+	//
+	// Shms in keysToIDs are guaranteed to be referenced, as they are
 	// removed by disassociateKey before the last DecRef.
-	keysToShms map[ipc.Key]*Shm
+	reg *ipc.Registry
 
 	// Sum of the sizes of all existing segments rounded up to page size, in
 	// units of page size.
 	totalPages uint64
-
-	// ID assigned to the last created segment. Used to quickly find the next
-	// unused ID.
-	lastIDUsed ipc.ID
 }
 
 // NewRegistry creates a new shm registry.
 func NewRegistry(userNS *auth.UserNamespace) *Registry {
 	return &Registry{
-		userNS:     userNS,
-		shms:       make(map[ipc.ID]*Shm),
-		keysToShms: make(map[ipc.Key]*Shm),
+		userNS: userNS,
+		reg:    ipc.NewRegistry(userNS),
 	}
 }
 
@@ -105,9 +101,14 @@ func NewRegistry(userNS *auth.UserNamespace) *Registry {
 func (r *Registry) FindByID(id ipc.ID) *Shm {
 	r.mu.Lock()
 	defer r.mu.Unlock()
-	s := r.shms[id]
+	mech := r.reg.FindByID(id)
+	if mech == nil {
+		return nil
+	}
+	s := mech.(*Shm)
+
 	// Take a reference on s. If TryIncRef fails, s has reached the last
-	// DecRef, but hasn't quite been removed from r.shms yet.
+	// DecRef, but hasn't quite been removed from r.reg.objects yet.
 	if s != nil && s.TryIncRef() {
 		return s
 	}
@@ -125,7 +126,7 @@ func (r *Registry) dissociateKey(s *Shm) {
 	s.mu.Lock()
 	defer s.mu.Unlock()
 	if s.obj.Key != linux.IPC_PRIVATE {
-		delete(r.keysToShms, s.obj.Key)
+		r.reg.DissociateKey(s.obj.Key)
 		s.obj.Key = linux.IPC_PRIVATE
 	}
 }
@@ -147,50 +148,29 @@ func (r *Registry) FindOrCreate(ctx context.Context, pid int32, key ipc.Key, siz
 	r.mu.Lock()
 	defer r.mu.Unlock()
 
-	if len(r.shms) >= linux.SHMMNI {
+	if r.reg.ObjectCount() >= linux.SHMMNI {
 		// "All possible shared memory IDs have been taken (SHMMNI) ..."
 		//   - man shmget(2)
 		return nil, syserror.ENOSPC
 	}
 
 	if !private {
-		// Look up an existing segment.
-		if shm := r.keysToShms[key]; shm != nil {
-			shm.mu.Lock()
-			defer shm.mu.Unlock()
-
-			// Check that caller can access the segment.
-			creds := auth.CredentialsFromContext(ctx)
-			if !shm.obj.CheckPermissions(creds, fs.PermsFromMode(mode)) {
-				// "The user does not have permission to access the shared
-				// memory segment, and does not have the CAP_IPC_OWNER
-				// capability in the user namespace that governs its IPC
-				// namespace." - man shmget(2)
-				return nil, linuxerr.EACCES
-			}
+		shm, err := r.reg.Find(ctx, key, mode, create, exclusive)
+		if err != nil {
+			return nil, err
+		}
 
+		// Validate shm-specific parameters.
+		if shm != nil {
+			shm := shm.(*Shm)
 			if size > shm.size {
 				// "A segment for the given key exists, but size is greater than
 				// the size of that segment." - man shmget(2)
 				return nil, linuxerr.EINVAL
 			}
-
-			if create && exclusive {
-				// "IPC_CREAT and IPC_EXCL were specified in shmflg, but a
-				// shared memory segment already exists for key."
-				//  - man shmget(2)
-				return nil, linuxerr.EEXIST
-			}
-
 			shm.IncRef()
 			return shm, nil
 		}
-
-		if !create {
-			// "No segment exists for the given key, and IPC_CREAT was not
-			// specified." - man shmget(2)
-			return nil, syserror.ENOENT
-		}
 	}
 
 	var sizeAligned uint64
@@ -208,9 +188,7 @@ func (r *Registry) FindOrCreate(ctx context.Context, pid int32, key ipc.Key, siz
 	}
 
 	// Need to create a new segment.
-	creator := fs.FileOwnerFromContext(ctx)
-	perms := fs.FilePermsFromMode(mode)
-	s, err := r.newShm(ctx, pid, key, creator, perms, size)
+	s, err := r.newShmLocked(ctx, pid, key, fs.FileOwnerFromContext(ctx), fs.FilePermsFromMode(mode), size)
 	if err != nil {
 		return nil, err
 	}
@@ -220,10 +198,10 @@ func (r *Registry) FindOrCreate(ctx context.Context, pid int32, key ipc.Key, siz
 	return s, nil
 }
 
-// newShm creates a new segment in the registry.
+// newShmLocked creates a new segment in the registry.
 //
 // Precondition: Caller must hold r.mu.
-func (r *Registry) newShm(ctx context.Context, pid int32, key ipc.Key, creator fs.FileOwner, perms fs.FilePermissions, size uint64) (*Shm, error) {
+func (r *Registry) newShmLocked(ctx context.Context, pid int32, key ipc.Key, creator fs.FileOwner, perms fs.FilePermissions, size uint64) (*Shm, error) {
 	mfp := pgalloc.MemoryFileProviderFromContext(ctx)
 	if mfp == nil {
 		panic(fmt.Sprintf("context.Context %T lacks non-nil value for key %T", ctx, pgalloc.CtxMemoryFileProvider))
@@ -235,39 +213,24 @@ func (r *Registry) newShm(ctx context.Context, pid int32, key ipc.Key, creator f
 		return nil, err
 	}
 
-	// Find the next available ID.
-	for id := r.lastIDUsed + 1; id != r.lastIDUsed; id++ {
-		// Handle wrap around.
-		if id < 0 {
-			id = 0
-			continue
-		}
-		if r.shms[id] == nil {
-			r.lastIDUsed = id
-
-			shm := &Shm{
-				mfp:           mfp,
-				registry:      r,
-				size:          size,
-				effectiveSize: effectiveSize,
-				obj:           ipc.NewObject(r.userNS, ipc.ID(id), ipc.Key(key), creator, creator, perms),
-				fr:            fr,
-				creatorPID:    pid,
-				changeTime:    ktime.NowFromContext(ctx),
-			}
-			shm.InitRefs()
-
-			r.shms[id] = shm
-			r.keysToShms[key] = shm
-
-			r.totalPages += effectiveSize / hostarch.PageSize
+	shm := &Shm{
+		mfp:           mfp,
+		registry:      r,
+		size:          size,
+		effectiveSize: effectiveSize,
+		obj:           ipc.NewObject(r.reg.UserNS, ipc.Key(key), creator, creator, perms),
+		fr:            fr,
+		creatorPID:    pid,
+		changeTime:    ktime.NowFromContext(ctx),
+	}
+	shm.InitRefs()
 
-			return shm, nil
-		}
+	if err := r.reg.Register(shm); err != nil {
+		return nil, err
 	}
+	r.totalPages += effectiveSize / hostarch.PageSize
 
-	log.Warningf("Shm ids exhuasted, they may be leaking")
-	return nil, syserror.ENOSPC
+	return shm, nil
 }
 
 // IPCInfo reports global parameters for sysv shared memory segments on this
@@ -289,7 +252,7 @@ func (r *Registry) ShmInfo() *linux.ShmInfo {
 	defer r.mu.Unlock()
 
 	return &linux.ShmInfo{
-		UsedIDs: int32(r.lastIDUsed),
+		UsedIDs: int32(r.reg.LastIDUsed()),
 		ShmTot:  r.totalPages,
 		ShmRss:  r.totalPages, // We could probably get a better estimate from memory accounting.
 		ShmSwp:  0,            // No reclaim at the moment.
@@ -310,7 +273,7 @@ func (r *Registry) remove(s *Shm) {
 		panic(fmt.Sprintf("Attempted to remove %s from the registry whose key is still associated", s.debugLocked()))
 	}
 
-	delete(r.shms, s.obj.ID)
+	r.reg.DissociateID(s.obj.ID)
 	r.totalPages -= s.effectiveSize / hostarch.PageSize
 }
 
@@ -322,13 +285,16 @@ func (r *Registry) Release(ctx context.Context) {
 	// 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.reg.ForAllObjects(
+		func(o ipc.Mechanism) {
+			s := o.(*Shm)
+			s.mu.Lock()
+			if !s.pendingDestruction {
+				toRelease = append(toRelease, s)
+			}
+			s.mu.Unlock()
+		},
+	)
 	r.mu.Unlock()
 
 	for _, s := range toRelease {
@@ -383,7 +349,6 @@ type Shm struct {
 	// mu protects all fields below.
 	mu sync.Mutex `state:"nosave"`
 
-	// obj defines basic fields that should be included in all SysV IPC objects.
 	obj *ipc.Object
 
 	// attachTime is updated on every successful shmat.
@@ -412,6 +377,28 @@ func (s *Shm) ID() ipc.ID {
 	return s.obj.ID
 }
 
+// Object implements ipc.Mechanism.Object.
+func (s *Shm) Object() *ipc.Object {
+	return s.obj
+}
+
+// Destroy implements ipc.Mechanism.Destroy. No work is performed on shm.Destroy
+// because a different removal mechanism is used in shm. See Shm.MarkDestroyed.
+func (s *Shm) Destroy() {
+}
+
+// Lock implements ipc.Mechanism.Lock.
+func (s *Shm) Lock() {
+	s.mu.Lock()
+}
+
+// Unlock implements ipc.mechanism.Unlock.
+//
+// +checklocksignore
+func (s *Shm) Unlock() {
+	s.mu.Unlock()
+}
+
 // Precondition: Caller must hold s.mu.
 func (s *Shm) debugLocked() string {
 	return fmt.Sprintf("Shm{id: %d, key: %d, size: %d bytes, refs: %d, destroyed: %v}",
diff --git a/pkg/sentry/syscalls/linux/sys_sem.go b/pkg/sentry/syscalls/linux/sys_sem.go
index 4755bef18..f61cc466c 100644
--- a/pkg/sentry/syscalls/linux/sys_sem.go
+++ b/pkg/sentry/syscalls/linux/sys_sem.go
@@ -240,7 +240,7 @@ func Semctl(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel.Syscal
 func remove(t *kernel.Task, id ipc.ID) error {
 	r := t.IPCNamespace().SemaphoreRegistry()
 	creds := auth.CredentialsFromContext(t)
-	return r.RemoveID(id, creds)
+	return r.Remove(id, creds)
 }
 
 func ipcSet(t *kernel.Task, id ipc.ID, uid auth.UID, gid auth.GID, perms fs.FilePermissions) error {