linux-kernel - Re: [PATCH V6 00/10] namespaces: log namespaces per task

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Date:	Fri, 8 May 2015 10:42:50 -0400
From:	Richard Guy Briggs <rgb@...hat.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	containers@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org, pmoore@...hat.com,
	linux-audit@...hat.com, eparis@...isplace.org, sgrubb@...hat.com,
	zohar@...ux.vnet.ibm.com
Subject: Re: [PATCH V6 00/10] namespaces: log namespaces per task

On 15/04/27, Eric W. Biederman wrote:
> Richard Guy Briggs <rgb@...hat.com> writes:
> > On 15/04/24, Eric W. Biederman wrote:
> >> Richard Guy Briggs <rgb@...hat.com> writes:
> >> > On 15/04/22, Richard Guy Briggs wrote:
> >> >> On 15/04/20, Eric W. Biederman wrote:
> >> >> > Richard Guy Briggs <rgb@...hat.com> writes:
> >> > Do I even need to report the device number anymore since I am concluding
> >> > s_dev is never set (or always zero) in the nsfs filesystem by
> >> > mount_pseudo() and isn't even mountable? 
> >> 
> >> We still need the dev. We do have a device number get_anon_bdev fills it in.
> >
> > Fine, it has a device number.  There appears to be only one of these
> > allocated per kernel.  I can get it from &nsfs->fs_supers (and take the
> > first instance given by hlist_for_each_entry and verify there are no
> > others).  Why do I need it, again?
> 
> Because if we have to preserve the inode number over a migration event I
> want to preserve the fact that we are talking about inode numbers from a
> superblock with a device number.
> 
> Otherwise known as I am allergic to kernel global identifiers, because
> they can be major pains.  I don't want to have to go back and implement
> a namespace for namespaces.

Alright, I'll change the device over to that...  We can figure out how
to select the correct device number of nsfs instances if it increases
beyond one.

> >> >> They are all covered:
> >> >> sys_unshare > unshare_userns > create_user_ns
> >> >> sys_unshare > unshare_nsproxy_namespaces > create_new_namespaces > copy_mnt_ns
> >> >> sys_unshare > unshare_nsproxy_namespaces > create_new_namespaces > copy_utsname > clone_uts_ns
> >> >> sys_unshare > unshare_nsproxy_namespaces > create_new_namespaces > copy_ipcs > get_ipc_ns
> >> >> sys_unshare > unshare_nsproxy_namespaces > create_new_namespaces > copy_pid_ns > create_pid_namespace
> >> >> sys_unshare > unshare_nsproxy_namespaces > create_new_namespaces > copy_net_ns
> >> 
> >> Then why the special change to fork?  That was not reflected on
> >> the unshare path as far as I could see.
> >
> > Fork can specify more than one CLONE flag at once, so collecting them
> > all in one statementn seemed helpful.  setns can only set one at a time.
> 
> unshare can also specify more than one CLONE flag at once.
> I just pointed that out becase that seemed really unsymmetrical.

Ah sorry, my mistake, I was thinking setns...  I've added a call in
sys_unshare().

> > Ok, understood, we can't just punt this one to a higher layer...
> >
> > So this comes back to a question above, which is how do we determine
> > which device it is from?  Sounds like we need something added to
> > ns_common or one of the 6 namespace types structs.
> 
> Or we can just hard code reading it off of the appropriate magic
> filesystem.  Probably what we want is a well named helper function that
> does the job.

There is a bit of overhead to read that, so I've added a dev_t member to
ns_common.  Simplest way I found was to call iterate_supers() since
struct file_system_type *nsfs isn't exposed.

> I just care that when we talk about these things we are talking about
> inode numbers from a superblock that is associated with a given device
> number.  That way I don't have nightmares about dealing with a namespace
> for namespaces.
> 
> Eric

- RGB

--
Richard Guy Briggs <rbriggs@...hat.com>
Senior Software Engineer, Kernel Security, AMER ENG Base Operating Systems, Red Hat
Remote, Ottawa, Canada
Voice: +1.647.777.2635, Internal: (81) 32635, Alt: +1.613.693.0684x3545
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