coredump: dump priviliges when processing system coredumps Let's add an extra-safety net and change UID/GID to the "systemd-coredump" user when processing coredumps from system user. For coredumps of normal users we keep the current logic of processing the coredumps from the user id the coredump was created under. Fixes: https://bugs.freedesktop.org/show_bug.cgi?id=87354

coredump: honour RLIMIT_CORE when saving/processing coredumps With this change processing/saving of coredumps takes the RLIMIT_CORE resource limit of the crashing process into account, given the user control whether specific processes shall core dump or not, and how large to make the core dump. Note that this effectively disables core-dumping for now, as RLIMIT_CORE defaults to 0 (i.e. is disabled) for all system processes.

coredump: rework coredumping logic This reworks the coredumping logic so that the coredump handler invoked from the kernel only collects runtime data about the crashed process, and then submits it for processing to a socket-activate coredump service, which extracts a stacktrace and writes the coredump to disk. This has a number of benefits: the disk IO and stack trace generation may take a substantial amount of resources, and hence should better be managed by PID 1, so that resource management applies. This patch uses RuntimeMaxSec=, Nice=, OOMScoreAdjust= and various sandboxing settings to ensure that the coredump handler doesn't take away unbounded resources from normally priorized processes. This logic is also nice since this makes sure the coredump processing and storage is delayed correctly until /var/systemd/coredump is mounted and writable. Fixes: #2286

build-sys: move coredump logic into subdir of its own