Re: bin/57952 (dhcpcd(8) inexplicably terminated in the night)

[Taylor R Campbell <riastradh%NetBSD.org@localhost>]

> Date: Fri, 23 Feb 2024 23:29:05 +0000
> From: Taylor R Campbell <riastradh%NetBSD.org@localhost>
> 
> So I infer that the network proxy must have crashed, in my original
> case.  But I don't see how to trigger a core dump.

Just in case somehow there's set-user/group-id processes involved, I
also tried:

1. make /var/chroot/dhcpcd/var/crash owned by _dhcpcd:_dhcpcd
2. add `kern.coredump.setid.dump=1' to /etc/modules.conf
3. reboot
4. kill -ABRT manager

I got a zero-length core file and a console message;

[ 1251.6878114] pid 6079 (dhcpcd): system write of 64@0xffffc000b03a79c0 at 0 failed: 27

I tried unlimiting the file size with

# sysctl -w proc.$pid.rlimit.filesize.hard=unlimited
# sysctl -w proc.$pid.rlimit.filesize.soft=unlimited

and this time, kill -ABRT manager produced a core dump at
/var/chroot/dhcpcd/var/crash/dhcpcd.core!

So there's several issues:

1. dhcpcd somehow gets the kern.coredump.setid treatment (which I
   thought was reserved for executables having the set-user/group-id
   bit set, and I don't see any evidence of that in dhcpcd)

2. /var/crash doesn't exist under the chroot, /var/chroot/dhcpcd

3. the filesize rlimit prevents the core dump too