Re: [PATCH v2] ANDROID: binder: Add BINDER_GET_NODE_INFO_FOR_REF ioctl.

[Todd Kjos <tkjos@google.com>]

On Fri, Sep 7, 2018 at 6:38 AM Martijn Coenen <maco@android.com> wrote:
>
> This allows the context manager to retrieve information about nodes
> that it holds a reference to, such as the current number of
> references to those nodes.
>
> Such information can for example be used to determine whether the
> servicemanager is the only process holding a reference to a node.
> This information can then be passed on to the process holding the
> node, which can in turn decide whether it wants to shut down to
> reduce resource usage.
>
> Signed-off-by: Martijn Coenen <maco@android.com>
> ---
> v2: made sure reserved fields are aligned, and enforce caller zeroes
>     all fields except handle, as suggested by Dan Carpenter.
>
>  drivers/android/binder.c            | 55 +++++++++++++++++++++++++++++
>  include/uapi/linux/android/binder.h | 10 ++++++
>  2 files changed, 65 insertions(+)
>
> diff --git a/drivers/android/binder.c b/drivers/android/binder.c
> index d58763b6b0090..5b25412e15ccf 100644
> --- a/drivers/android/binder.c
> +++ b/drivers/android/binder.c
> @@ -4544,6 +4544,42 @@ static int binder_ioctl_set_ctx_mgr(struct file *filp)
>         return ret;
>  }
>
> +static int binder_ioctl_get_node_info_for_ref(struct binder_proc *proc,
> +               struct binder_node_info_for_ref *info)
> +{
> +       struct binder_node *node;
> +       struct binder_context *context = proc->context;
> +       __u32 handle = info->handle;
> +
> +       if (info->strong_count || info->weak_count || info->reserved1 ||
> +           info->reserved2 || info->reserved3) {
> +               binder_user_error("%d BINDER_GET_NODE_INFO_FOR_REF: only handle may be non-zero.",
> +                                 proc->pid);
> +               return -EINVAL;
> +       }
> +
> +       /* This ioctl may only be used by the context manager */
> +       mutex_lock(&context->context_mgr_node_lock);
> +       if (!context->binder_context_mgr_node ||
> +               context->binder_context_mgr_node->proc != proc) {
> +               mutex_unlock(&context->context_mgr_node_lock);
> +               return -EPERM;
> +       }
> +       mutex_unlock(&context->context_mgr_node_lock);
> +
> +       node = binder_get_node_from_ref(proc, handle, true, NULL);
> +       if (!node)
> +               return -EINVAL;
> +
> +       info->strong_count = node->local_strong_refs +
> +               node->internal_strong_refs;
> +       info->weak_count = node->local_weak_refs;

Aren't we under-reporting the weak refs here? The "internal weak" refs
are the count of elements in node->refs, so we need to add something
like:

hlist_for_each_entry(ref, &node->refs, node_entry)
        info->weak_count++;

> +
> +       binder_put_node(node);
> +
> +       return 0;
> +}
> +
>  static int binder_ioctl_get_node_debug_info(struct binder_proc *proc,
>                                 struct binder_node_debug_info *info)
>  {
> @@ -4638,6 +4674,25 @@ static long binder_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
>                 }
>                 break;
>         }
> +       case BINDER_GET_NODE_INFO_FOR_REF: {
> +               struct binder_node_info_for_ref info;
> +
> +               if (copy_from_user(&info, ubuf, sizeof(info))) {
> +                       ret = -EFAULT;
> +                       goto err;
> +               }
> +
> +               ret = binder_ioctl_get_node_info_for_ref(proc, &info);
> +               if (ret < 0)
> +                       goto err;
> +
> +               if (copy_to_user(ubuf, &info, sizeof(info))) {
> +                       ret = -EFAULT;
> +                       goto err;
> +               }
> +
> +               break;
> +       }
>         case BINDER_GET_NODE_DEBUG_INFO: {
>                 struct binder_node_debug_info info;
>
> diff --git a/include/uapi/linux/android/binder.h b/include/uapi/linux/android/binder.h
> index bfaec6903b8bc..b9ba520f7e4bb 100644
> --- a/include/uapi/linux/android/binder.h
> +++ b/include/uapi/linux/android/binder.h
> @@ -200,6 +200,15 @@ struct binder_node_debug_info {
>         __u32            has_weak_ref;
>  };
>
> +struct binder_node_info_for_ref {
> +       __u32            handle;
> +       __u32            strong_count;
> +       __u32            weak_count;
> +       __u32            reserved1;
> +       __u32            reserved2;
> +       __u32            reserved3;
> +};
> +
>  #define BINDER_WRITE_READ              _IOWR('b', 1, struct binder_write_read)
>  #define BINDER_SET_IDLE_TIMEOUT                _IOW('b', 3, __s64)
>  #define BINDER_SET_MAX_THREADS         _IOW('b', 5, __u32)
> @@ -208,6 +217,7 @@ struct binder_node_debug_info {
>  #define BINDER_THREAD_EXIT             _IOW('b', 8, __s32)
>  #define BINDER_VERSION                 _IOWR('b', 9, struct binder_version)
>  #define BINDER_GET_NODE_DEBUG_INFO     _IOWR('b', 11, struct binder_node_debug_info)
> +#define BINDER_GET_NODE_INFO_FOR_REF   _IOWR('b', 12, struct binder_node_info_for_ref)
>
>  /*
>   * NOTE: Two special error codes you should check for when calling
> --
> 2.19.0.rc2.392.g5ba43deb5a-goog
>