devpts: IterDirents has to check offset and return if it is out of range

panic: runtime error: slice bounds out of range [124:0]

goroutine 136 [running]:
panic({0x3ef9e0?, 0xc000848b28?})
	GOROOT/src/runtime/panic.go:1017
runtime.goPanicSliceB(0x7c, 0x0)
	GOROOT/src/runtime/panic.go:154
gvisor.dev/gvisor/pkg/sentry/fsimpl/devpts.(*rootInode).IterDirents
	pkg/sentry/fsimpl/devpts/devpts.go:342
gvisor.dev/gvisor/pkg/sentry/fsimpl/kernfs.(*GenericDirectoryFD).IterDirents
	pkg/sentry/fsimpl/kernfs/fd_impl_util.go:224

Reported-by: syzbot+4c8983831b3b9c7feff6@syzkaller.appspotmail.com
PiperOrigin-RevId: 583183528

pkg/sentry/fsimpl/devpts/devpts.go

@@ -334,6 +334,9 @@ func (i *rootInode) IterDirents(ctx context.Context, mnt *vfs.Mount, cb vfs.Iter
 	i.mu.Lock()
 	defer i.mu.Unlock()
 	i.InodeAttrs.TouchAtime(ctx, mnt)
+	if relOffset >= int64(len(i.replicas)) {
+		return offset, nil
+	}
 	ids := make([]int, 0, len(i.replicas))
 	for id := range i.replicas {
 		ids = append(ids, int(id))