Samsung Android JACK ASLR Bypass

The usermode audio subsystem for the "Samsung Android Professional Audio" is based on JACK, which appears to be designed for single-user usage. The common JACK configuration on Linux systems appears to be a JACK server running under the current user account, and interacting with JACK clients from the same user account; so with a minimal privilege difference; this is not the case with the configuration on Android, where the JACK service runs as a more privileged user in a less restrictive SELinux domain to the clients that can connect to it. The JACK shared memory implementation uses the struct jack_shm_info_t defined in /common/shm.h to do some bookkeeping. This struct is stored at the start of every JackShmAble object. This means that whenever the JACK server creates an object backed by shared memory, it also stores a pointer to that object (in the address space of the JACK server), allowing a malicious client to bypass ASLR in the JACK server process.