Hi.
On Sun, Apr 22, 2018 at 09:07:04AM +0000, Curt wrote:
> On 2018-04-22, David Wright <deblis@lionunicorn.co.uk> wrote:
> >>
> >> I am not after winning any races but (seeing as you brought the issue
> >> up) knowing whether ps sees my secret and how to go about finding that
> >> out.
> >
> > ps might not be the best tool for deliberately finding the info above.
> > The obvious place to look is /proc/<PID>/cmdline (where NULs separate
> > the items). One can imagine a scenario where one tries to keep up with
> > the PID incrementation and hoover up all the cmdlines on the system as
> > they fly by.
> >
>
> There is a mount option to the proc filesystem ('hidepid') that appears
> to be designed to harden against the envisioned scenario (if I'm
> understanding correctly--may not be the case, though).
>
> https://debian-administration.org/article/702/Hiding_processes_from_other_users
>
> Perhaps this is now obsolete information or something.
No, it's slightly outdated (they don't put /proc entry in fstab in
stretch by default), but still useful.
> Maybe not because in my Stretch man page for proc right at the top
> I see the hidepid mount option.
It's in the kernel documentation:
/usr/share/doc/linux-doc-4.9/Documentation/filesystems/proc.txt.gz
and it works:
$ id
uid=1000(user) gid=1000(user) groups=1000(user)...
$ mount | grep proc
proc on /proc type proc (rw,relatime,hidepid=2)
systemd-1 on /proc/sys/fs/binfmt_misc type autofs (rw,relatime,fd=32,pgrp=1,timeout=0,minproto=5,maxproto=5,direct,pipe_ino=8539)
binfmt_misc on /proc/sys/fs/binfmt_misc type binfmt_misc (rw,relatime)
$ ls -d /proc/[0-9]* | wc -l
3
> Here (from 2014)
>
> https://lists.debian.org/debian-devel-announce/2014/03/msg00004.html
>
> it is said "* We're planning to request for hidepid to be enabled by
> default (to 1). This will squash an entire class of information leaks. If
> you have any comments or objections, please get in touch with us.
>
> but I can't seem to discover whether that was realized or not--from what
> you people are saying, I guess not (hidepid=1 doesn't appear as a proc
> mount option on my upgraded since Methuselah Stretch machine).
That's because it's not a default setting. My guess is a certain Modern
Desktop Environment™ breaks somehow if hidepid > 0 is in use.
Reco