CVE-2018-15004: Medium severity coolpad canvas vulnerability

The Coolpad Canvas device with a build fingerprint of Coolpad/cp3636a/cp3636a:7.0/NRD90M/093031423:user/release-keys contains a platform app with a package name of com.qualcomm.qti.modemtestmode (versionCode=24, versionName=7.0) that contains an exported service app component named com.qualcomm.qti.modemtestmode.MbnTestService that allows any app on the device to set certain system properties as the com.android.phone user. When an app sets the persist.service.logr.enable system property to a value of 1, an app with a package name of com.yulong.logredirect (versionCode=20160622, versionName=5.252016062201) will start writing the system-wide logcat log, kernel log, and a tcpdump network traffic capture to external storage. Furthermore, on the Coolpad Canvas device, the com.android.phone app writes the destination phone number and body of the text message for outgoing text messages. A notification when logging can be avoided if the log is enabled after device startup and disabled prior to device shutdown by setting the system properties using the exported interface of the com.qualcomm.qti.modemtestmode app. Any app with the READEXTERNALSTORAGE permission can access the log files.