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

[Martijn Coenen]

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@xxxxxxxxxxx>
---
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;
+
+	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