On Tue, 2013-07-30 at 08:07 -0400, Simo Sorce wrote:
> On Tue, 2013-07-30 at 03:27 +0200, Lennart Poettering wrote:
> > On Mon, 29.07.13 21:11, Simo Sorce (simo@xxxxxxxxxx) wrote:
> >
> > > On Tue, 2013-07-30 at 02:08 +0200, Lennart Poettering wrote:
> > > > On Mon, 29.07.13 23:56, David Woodhouse (dwmw2@xxxxxxxxxxxxx) wrote:
> > > >
> > > > > On Tue, 2013-07-30 at 00:50 +0200, Lennart Poettering wrote:
> > > > > > So, why don't you revert to using /tmp then?
> > > > >
> > > > > The problem with /tmp is that if you want predictable filenames for the
> > > > > storage, you open yourself to a denial-of-service attack where another
> > > > > user can create a file with the same name.
> > > >
> > > > Well, but that's not unsurmountable, just pick a randomly named
> > > > directory in /tmp and make sure to have a symlink:
> > > >
> > > > ln -s /tmp/krb.XXXXXX "$HOME/.krb-`cat /etc/machine-id`"
> > >
> > > What would create this directory ?
> >
> > The same component that creates the temporary directory?
> >
> > In pseudo code:
> >
> > char temp[] = "/tmp/krb.XXXXXX", link[PATH_MAX];
> > char *machine_id, *home;
> >
> > mkdtemp(temp);
> > machine_id = get_file_contents("/etc/machine_id");
> > *strchrnul(machined_id, '\n') = 0;
> > home = getenv("HOME);
> > snprintf(link, "%s/.krb-%s", home, machine_id);
> > symlink(temp, link);
> >
> > Of course, you should skip this if the symlink already exists and points
> > to a valid directory...
>
> This doesn't make any sense whatsoever, if we are back to unpredictable
> file names and trolling I may as well just use /tmp/krb5cc_XXXXXX only.
>
> Ccaches do not belong in the home directory, period.
Couldn't agree more.
There's no guarantee the home directory will be available when the
credential is needed.
>
> > > > to give it a stable, machine-local name.
> > >
> > > in what case /tmp contains non-'machine-local' files ?
> >
> > /tmp doesn't. But /home does. Hence you include the machine ID in the
> > symlink name.
> >
> > > Also I need one directory per-user and not per-machine.
> >
> > Well, you want it per-user *and* per-machine.
> >
> > > And how is this different than /run/kerberos in the end ?
> >
> > That there's a sane cleanup scheme done via /tmp and not yet another
> > place where we have unrestricted runtime objects of the user.
>
> Except the stuff that cleans /tmp has no idea how to look *into* the
> ccache to see if it is still valid or not, so it is a mechanism I do not
> care for.
>
> Simo.
>
> --
> Simo Sorce * Red Hat, Inc * New York
>
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