dmesgd: sepolicies

dmesgd is a daemon that collects kernel memory error reports.

When system_server notices that a kernel error occured, it sets the
dmesgd.start system property to 1, which results in init starting

Once that happens, dmesgd runs `dmesg` and parses its output to collect
the last error report. That report, together with the headers containing
device- and build-specific information is stored in Dropbox.

Empirically, dmesgd needs the following permissions:
- execute shell (for popen()) and toolbox (for dmesg),
  read system_log (for dmesg)
- read /proc/version (to generate headers)
- perform Binder calls to servicemanager and system_server,
  find dropbox_service (for dropbox)
- create files in /data/misc/dmesgd (to store persistent state)

Bug: 215095687
Test: run dmesgd on a user device with injected KFENCE bugs
Change-Id: Iff21a2ffd99fc31b89a58ac774299b5e922721ea
6 files changed