Add type safety to shm ids and keys.

PiperOrigin-RevId: 224864380
Change-Id: I49542279ad56bf15ba462d3de1ef2b157b31830a

pkg/sentry/kernel/shm/shm.go

@@ -51,6 +51,12 @@ import (
 	"gvisor.googlesource.com/gvisor/pkg/syserror"
 )
 
+// Key represents a shm segment key. Analogous to a file name.
+type Key int32
+
+// ID represents the opaque handle for a shm segment. Analogous to an fd.
+type ID int32
+
 // Registry tracks all shared memory segments in an IPC namespace. The registry
 // provides the mechanisms for creating and finding segments, and reporting
 // global shm parameters.
@@ -63,33 +69,33 @@ type Registry struct {
 	mu sync.Mutex `state:"nosave"`
 
 	// shms maps segment ids to segments. Protected by mu.
-	shms map[int32]*Shm
+	shms map[ID]*Shm
 
 	// Sum of the sizes of all existing segments rounded up to page size, in
 	// units of page size. Protected by mu.
 	totalPages uint64
 
 	// lastIDUsed is protected by mu.
-	lastIDUsed int32
+	lastIDUsed ID
 }
 
 // NewRegistry creates a new shm registry.
 func NewRegistry(userNS *auth.UserNamespace) *Registry {
 	return &Registry{
 		userNS: userNS,
-		shms:   make(map[int32]*Shm),
+		shms:   make(map[ID]*Shm),
 	}
 }
 
 // FindByID looks up a segment given an ID.
-func (r *Registry) FindByID(id int32) *Shm {
+func (r *Registry) FindByID(id ID) *Shm {
 	r.mu.Lock()
 	defer r.mu.Unlock()
 	return r.shms[id]
 }
 
 // Precondition: Caller must hold r.mu.
-func (r *Registry) findByKey(key int32) *Shm {
+func (r *Registry) findByKey(key Key) *Shm {
 	for _, v := range r.shms {
 		if v.key == key {
 			return v
@@ -100,7 +106,7 @@ func (r *Registry) findByKey(key int32) *Shm {
 
 // FindOrCreate looks up or creates a segment in the registry. It's functionally
 // analogous to open(2).
-func (r *Registry) FindOrCreate(ctx context.Context, pid, key int32, size uint64, mode linux.FileMode, private, create, exclusive bool) (*Shm, error) {
+func (r *Registry) FindOrCreate(ctx context.Context, pid int32, key Key, size uint64, mode linux.FileMode, private, create, exclusive bool) (*Shm, error) {
 	if (create || private) && (size < linux.SHMMIN || size > linux.SHMMAX) {
 		// "A new segment was to be created and size is less than SHMMIN or
 		// greater than SHMMAX." - man shmget(2)
@@ -178,7 +184,7 @@ func (r *Registry) FindOrCreate(ctx context.Context, pid, key int32, size uint64
 }
 
 // newShm creates a new segment in the registry.
-func (r *Registry) newShm(ctx context.Context, pid, key int32, creator fs.FileOwner, perms fs.FilePermissions, size uint64) (*Shm, error) {
+func (r *Registry) newShm(ctx context.Context, pid int32, key Key, creator fs.FileOwner, perms fs.FilePermissions, size uint64) (*Shm, error) {
 	p := platform.FromContext(ctx)
 	if p == nil {
 		panic(fmt.Sprintf("context.Context %T lacks non-nil value for key %T", ctx, platform.CtxPlatform))
@@ -289,7 +295,7 @@ type Shm struct {
 	registry *Registry
 
 	// ID is the kernel identifier for this segment. Immutable.
-	ID int32
+	ID ID
 
 	// creator is the user that created the segment. Immutable.
 	creator fs.FileOwner
@@ -309,7 +315,7 @@ type Shm struct {
 	fr platform.FileRange
 
 	// key is the public identifier for this segment.
-	key int32
+	key Key
 
 	// mu protects all fields below.
 	mu sync.Mutex `state:"nosave"`

pkg/sentry/syscalls/linux/sys_shm.go

@@ -24,7 +24,7 @@ import (
 
 // Shmget implements shmget(2).
 func Shmget(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel.SyscallControl, error) {
-	key := args[0].Int()
+	key := shm.Key(args[0].Int())
 	size := uint64(args[1].SizeT())
 	flag := args[2].Int()
 
@@ -43,7 +43,7 @@ func Shmget(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel.Syscal
 }
 
 // findSegment retrives a shm segment by the given id.
-func findSegment(t *kernel.Task, id int32) (*shm.Shm, error) {
+func findSegment(t *kernel.Task, id shm.ID) (*shm.Shm, error) {
 	r := t.IPCNamespace().ShmRegistry()
 	segment := r.FindByID(id)
 	if segment == nil {
@@ -55,7 +55,7 @@ func findSegment(t *kernel.Task, id int32) (*shm.Shm, error) {
 
 // Shmat implements shmat(2).
 func Shmat(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel.SyscallControl, error) {
-	id := args[0].Int()
+	id := shm.ID(args[0].Int())
 	addr := args[1].Pointer()
 	flag := args[2].Int()
 
@@ -86,7 +86,7 @@ func Shmdt(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel.Syscall
 
 // Shmctl implements shmctl(2).
 func Shmctl(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel.SyscallControl, error) {
-	id := args[0].Int()
+	id := shm.ID(args[0].Int())
 	cmd := args[1].Int()
 	buf := args[2].Pointer()