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

[Christos Zoulas <christos%zoulas.com@localhost>]

The following reply was made to PR bin/57952; it has been noted by GNATS.

From: Christos Zoulas <christos%zoulas.com@localhost>
To: Taylor R Campbell <riastradh%NetBSD.org@localhost>
Cc: Roy Marples <roy%marples.name@localhost>,
 "gnats-bugs%netbsd.org@localhost" <gnats-bugs%NetBSD.org@localhost>,
 Martin Husemann <martin%duskware.de@localhost>,
 "gnats-admin%netbsd.org@localhost" <gnats-admin%NetBSD.org@localhost>,
 "netbsd-bugs%netbsd.org@localhost" <netbsd-bugs%NetBSD.org@localhost>
Subject: Re: bin/57952 (dhcpcd(8) inexplicably terminated in the night)
Date: Fri, 23 Feb 2024 19:50:16 -0500

        if (USPACE + ctob(vm->vm_dsize + vm->vm_ssize) >=3D
             p->p_rlimit[RLIMIT_CORE].rlim_cur) {
                 error =3D EFBIG;          /* better error code? */
                 goto release;
         }
 
 Looks like the core resource limit is 0?
 
 christos
 
 > On Feb 23, 2024, at 7:48=E2=80=AFPM, Taylor R Campbell =
 <riastradh%NetBSD.org@localhost> wrote:
 >=20
 >> Date: Fri, 23 Feb 2024 23:29:05 +0000
 >> From: Taylor R Campbell <riastradh%NetBSD.org@localhost>
 >>=20
 >> 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.
 >=20
 > Just in case somehow there's set-user/group-id processes involved, I
 > also tried:
 >=20
 > 1. make /var/chroot/dhcpcd/var/crash owned by _dhcpcd:_dhcpcd
 > 2. add `kern.coredump.setid.dump=3D1' to /etc/modules.conf
 > 3. reboot
 > 4. kill -ABRT manager
 >=20
 > I got a zero-length core file and a console message;
 >=20
 > [ 1251.6878114] pid 6079 (dhcpcd): system write of =
 64@0xffffc000b03a79c0 at 0 failed: 27
 >=20
 > I tried unlimiting the file size with
 >=20
 > # sysctl -w proc.$pid.rlimit.filesize.hard=3Dunlimited
 > # sysctl -w proc.$pid.rlimit.filesize.soft=3Dunlimited
 >=20
 > and this time, kill -ABRT manager produced a core dump at
 > /var/chroot/dhcpcd/var/crash/dhcpcd.core!
 >=20
 > So there's several issues:
 >=20
 > 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)
 >=20
 > 2. /var/crash doesn't exist under the chroot, /var/chroot/dhcpcd
 >=20
 > 3. the filesize rlimit prevents the core dump too