Fix capability check for sysv semaphores.

Capabilities for sysv sem operations were being checked against the
current task's user namespace. They should be checked against the user
namespace owning the ipc namespace for the sems instead, per
ipc/util.c:ipcperms().

PiperOrigin-RevId: 197063111

pkg/sentry/kernel/ipc_namespace.go

@@ -33,7 +33,7 @@ type IPCNamespace struct {
 func NewIPCNamespace(userNS *auth.UserNamespace) *IPCNamespace {
 	return &IPCNamespace{
 		userNS:     userNS,
-		semaphores: semaphore.NewRegistry(),
+		semaphores: semaphore.NewRegistry(userNS),
 		shms:       shm.NewRegistry(userNS),
 	}
 }

pkg/sentry/kernel/semaphore/semaphore.go

@@ -43,6 +43,8 @@ const (
 
 // Registry maintains a set of semaphores that can be found by key or ID.
 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[int32]*Set
@@ -51,6 +53,9 @@ type Registry struct {
 
 // Set represents a set of semaphores that can be operated atomically.
 type Set struct {
+	// registry owning this sem set. Immutable.
+	registry *Registry
+
 	// Id is a handle that identifies the set.
 	ID int32
 
@@ -90,8 +95,11 @@ type waiter struct {
 }
 
 // NewRegistry creates a new semaphore set registry.
-func NewRegistry() *Registry {
-	return &Registry{semaphores: make(map[int32]*Set)}
+func NewRegistry(userNS *auth.UserNamespace) *Registry {
+	return &Registry{
+		userNS:     userNS,
+		semaphores: make(map[int32]*Set),
+	}
 }
 
 // FindOrCreate searches for a semaphore set that matches 'key'. If not found,
@@ -175,6 +183,7 @@ func (r *Registry) RemoveID(id int32, creds *auth.Credentials) error {
 
 func (r *Registry) newSet(ctx context.Context, key int32, owner, creator fs.FileOwner, perms fs.FilePermissions, nsems int32) (*Set, error) {
 	set := &Set{
+		registry:   r,
 		key:        key,
 		owner:      owner,
 		creator:    owner,
@@ -415,7 +424,7 @@ func (s *Set) checkCredentials(creds *auth.Credentials) bool {
 }
 
 func (s *Set) checkCapability(creds *auth.Credentials) bool {
-	return creds.HasCapability(linux.CAP_IPC_OWNER) && creds.UserNamespace.MapFromKUID(s.owner.UID).Ok()
+	return creds.HasCapabilityIn(linux.CAP_IPC_OWNER, s.registry.userNS) && creds.UserNamespace.MapFromKUID(s.owner.UID).Ok()
 }
 
 func (s *Set) checkPerms(creds *auth.Credentials, reqPerms fs.PermMask) bool {

pkg/sentry/kernel/semaphore/semaphore_test.go

@@ -136,7 +136,7 @@ func TestNoWait(t *testing.T) {
 
 func TestUnregister(t *testing.T) {
 	ctx := contexttest.Context(t)
-	r := NewRegistry()
+	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)