Let's make sure that user's cannot DoS services for other users so
easily, and enable MaxConnectionsPerSocket= by default for all of them.
Note that this is mostly paranoia for systemd-pcrextend.socket and
systemd-sysext.socket: the socket is only accessible to root anyway,
hence the accounting shouldn#t change anything. But this is just a
safety net, in preparation that we open up some functionality of these
services sooner or later.
It's a bit nicer if we only write the sysctl core_pattern once the
coredump socket is established, since it's the backend for the handler.
Given the systemd-coredump.socket basically has no dependencies that run
before it this should not really make things slower or so, it just
removes the tiny window where core pattern is in effect that wants to
connect to the backend socket but cannot.
The status quo isn't terrible, and not too different in effect: either
way, until the socket unit is up we won't process coredumps. It's mostly
what kind of behaviour you get then: an error due to /bin/false being
invoked, or an error because systemd-coredump can't connect to its
socket. After this patch we'll exclusively see the former.
Otherwise a coredump started at the inconvinient moment can stop
shutdown.target leaving the system in a halfway-down state:
Pulling in shutdown.target/start from systemd-poweroff.service/start
Added job shutdown.target/start to transaction.
...
Keeping job shutdown.target/start because of systemd-poweroff.service/start
...
[ OK ] Stopped target Remote File Systems.
shutdown.target: starting held back, waiting for: systemd-networkd.socket
sysinit.target: stopping held back, waiting for: remount_tmp.service
systemd-coredump.socket: Incoming traffic
...
systemd-coredump@0-243-0.service: Trying to enqueue job systemd-coredump@0-243-0.service/start/replace
Added job systemd-coredump@0-243-0.service/start to transaction.
Pulling in systemd-journald.socket/start from systemd-coredump@0-243-0.service/start
Added job systemd-journald.socket/start to transaction.
Pulling in system.slice/start from systemd-journald.socket/start
Added job system.slice/start to transaction.
Pulling in -.slice/start from system.slice/start
Added job -.slice/start to transaction.
Pulling in system-systemd\x2dcoredump.slice/start from systemd-coredump@0-243-0.service/start
Added job system-systemd\x2dcoredump.slice/start to transaction.
Pulling in system.slice/start from system-systemd\x2dcoredump.slice/start
Pulling in shutdown.target/stop from system-systemd\x2dcoredump.slice/start
Added job shutdown.target/stop to transaction.
...
Keeping job systemd-poweroff.service/stop because of umount.target/stop
Keeping job shutdown.target/stop because of systemd-coredump@0-243-0.service/start
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
