[ovs-discuss] Handling conf.db ownership on OVS_USER_ID changes

Numan Siddique nusiddiq at redhat.com
Thu May 2 13:50:28 UTC 2019


On Mon, Apr 29, 2019, 9:36 PM Aaron Conole <aconole at redhat.com> wrote:

> Jaime Caamaño Ruiz <jcaamano at suse.de> writes:
>
> >> As a "security concern" you mean something among the lines where one
> >> of ovs-* processes running under openvswitch user would go ahead and
> >> create a file with its owner that later one of ovn processes would
> >> blindly reuse without checking that it actually belongs to root:root?
> >
> > One example is that the OVS user could create link as any OVN log file
> > to other file owned by root and then OVN would write to that file.
>
> There's a long-standing issue of OVN running as root.  I don't see any
> reason it should.
>

Agree. I will try to address this issue. I think we can have a separate
run time/log directory for OVN. ovn-controller needs to talk to the local
ovsdb-server
and br-int.mgmt and other related socket interfaces, so it needs access to
the /var/run/openvswitch/ folder. I think we can solve this.

Thanks
Numan


> >> Can you give a more concrete example? I believe logrotate is running
> >> under root and should be able to rotate everything?
> >
> > The logrotate configuration for openvswitch logs has a 'su' directive
> > to run under the openvswitch user, precisely to prevent something
> > similar to the above. So it wont be able to rotate root owned logs in
> > the openvswitch directory. How it fails precisely depends on global
> > logrotate configuration. For example it will fail to create the new log
> > file after rotation if the 'create' directive is used. Or it may fail
> > to compress the rotated log file as it wont be able to read it.
> >
> > BR
> > Jaime
> >
> > -----Original Message-----
> > From: Ansis Atteka <ansisatteka at gmail.com>
> > To: jcaamano at suse.de
> > Cc: ovs-discuss at openvswitch.org, Ben Pfaff <blp at ovn.org>
> > Subject: Re: [ovs-discuss] Handling conf.db ownership on OVS_USER_ID
> > changes
> > Date: Wed, 24 Apr 2019 19:07:24 -0700
> >
> > On Tue, 23 Apr 2019 at 09:30, Jaime Caamaño Ruiz <jcaamano at suse.de>
> > wrote:
> >>
> >> Hello
> >>
> >> So the non root owned log directory (and run directory) is shared
> >> between non root OVS processes and root OVN processes. Doesn't this
> >> raise some security concerns?
> >
> > As a "security concern" you mean something among the lines where one
> > of ovs-* processes running under openvswitch user would go ahead and
> > create a file with its owner that later one of ovn processes would
> > blindly reuse without checking that it actually belongs to root:root?
> >
> >
> >>
> >> Also, since logrotate rotates the logs with the OVS user, it may fail
> >> to some extent to rotate the root owned OVN log files. Consequences
> >> vary but in it's current state some logging might be lost. This could
> >> be improved but I would guess that the approprioate thing to do is to
> >> etiher use a different log directory for OVN or make its processes
> >> run
> >> with the OVS user also. Has any of this been considered?
> >
> > Can you give a more concrete example? I believe logrotate is running
> > under root and should be able to rotate everything?
> >
> >
> >>
> >> BR
> >> Jaime.
> >>
> >>
> >> -----Original Message-----
> >> From: Jaime Caamaño Ruiz <jcaamano at suse.de>
> >> Reply-to: jcaamano at suse.com
> >> To: Ansis Atteka <ansisatteka at gmail.com>
> >> Cc: ovs-discuss at openvswitch.org, Ben Pfaff <blp at ovn.org>
> >> Subject: Re: [ovs-discuss] Handling conf.db ownership on OVS_USER_ID
> >> changes
> >> Date: Wed, 17 Apr 2019 12:52:32 +0200
> >>
> >> > You also need to chown /var/log/openvswitch.*.log files.
> >>
> >> OVS seems to be already handling this. I dont know the details but I
> >> guess that before dropping capabilities, OVS chowns these by itself.
> >>
> >> > However,
> >> > what about other daemons, like ovn? Do they share run time dir?
> >> > Haven't looked into this in a while and don't have a setup to check
> >> > myself.
> >>
> >> The permisions of the openvswitch run directory are already being
> >> handled by the service unit file. There is read access to files
> >> created
> >> there by OVS and AFAIK what it ultimately makes it a no problem for
> >> OVN
> >> is that it still runs as root with the provided unit files. If anyone
> >> changes this to a user different than the openvswitch user, then that
> >> is an already existing issue. Am I missing something here?
> >>
> >> Agree with you other considerations.
> >>
> >> BR
> >> Jaime.
> >>
> >> -----Original Message-----
> >> From: Ansis Atteka <ansisatteka at gmail.com>
> >> To: jcaamano at suse.de
> >> Cc: ovs-discuss at openvswitch.org, Ben Pfaff <blp at ovn.org>
> >> Subject: Re: [ovs-discuss] Handling conf.db ownership on OVS_USER_ID
> >> changes
> >> Date: Tue, 16 Apr 2019 18:21:48 -0700
> >>
> >> On Tue, 16 Apr 2019 at 17:20, Jaime Caamaño Ruiz <jcaamano at suse.de>
> >> wrote:
> >> >
> >> > My intention was doing it at systemd unit (prestart) for file
> >> > conf.db
> >> > (and .conf.db.~lock~ that stays around) only.
> >>
> >> You also need to chown /var/log/openvswitch.*.log files.
> >> >
> >> > I was not thinking on absolutely fool proof mechanism, among other
> >> > things because the admin might have customized the location for the
> >> > database. Also, updating and restarting the service are things that
> >> > would usually be monitored. So best effort.
> >>
> >> make sure that best effort solution informs admin in case of error so
> >> that he does not have to go file by file to find the offending one.
> >>
> >> >
> >> > At systemd unit prestart the service is stopped and OVS nor nobody
> >> > should really be messing with the database files owned by OVS. If
> >> > the
> >> > spec file is changing things back to root unappropriately then that
> >> > should be changed too.
> >>
> >> Yes.
> >>
> >> >
> >> > The runtime /run/openvswitch directory is also controlled by
> >> > systemd
> >> > and at least on my system is removed if the service is not active,
> >> > either by graceful or ungraceful exit.
> >>
> >> I somewhat agree with this, because back in those days we were using
> >> SystemV where the init.d managed lifecycle of run directory..
> >> However,
> >> what about other daemons, like ovn? Do they share run time dir?
> >> Haven't looked into this in a while and don't have a setup to check
> >> myself.
> >>
> >> >
> >> > I guess we will need to look for specific issues. Any hint to find
> >> > that
> >> > patch?
> >>
> >> 1. test upgrade to your patched OVS and also from your patched OVS to
> >> another future version
> >> 2. if you change existing spec files that are shared with on Fedora
> >> or
> >> RHEL/CentOS make sure you don't break anything for them.
> >> 3. prefer consistency w.r.t. default behavior across deb and rpm
> >> packages (if you change user by default consider to do that for all
> >> platforms)
> >> 4. besides database you will also need to set right access bits to
> >> log
> >> files. On my Ubuntu it is "-rw-r----- 1 root adm " which means:
> >> 4.1. you have to chown it; OR
> >> 4.2. add openvswitch user to adm group and chmod that file
> >> 5. test logrotation. Maybe you can use a one forced logrotation
> >> invocation to change the ownrer.
> >> 6. check that other stuff like ovs-monitor-ipsec is not affected. It
> >> stil need to talk with StrongSwan or libreswan that best to my
> >> knowledge still runs as root.
> >> 7. if you use USER= then:
> >> 7.1. For Linux datapath make sure you retain CAP_NET_ADMIN Linux
> >> Capabilities
> >> 7.2. I don't know if there are special privileges you need to retain
> >> for DPDK. And in future possibly AF_XDP.
> >> 8. I haven't looked in a while but check if ovn (that has its own
> >> Systemd service file) shares run dir with OVS
> >>
> >> >
> >> > BR
> >> > Jaime.
> >> >
> >> > -----Original Message-----
> >> > From: Ansis Atteka <ansisatteka at gmail.com>
> >> > To: jcaamano at suse.de
> >> > Cc: ovs-discuss at openvswitch.org, Ben Pfaff <blp at ovn.org>
> >> > Subject: Re: [ovs-discuss] Handling conf.db ownership on
> >> > OVS_USER_ID
> >> > changes
> >> > Date: Tue, 16 Apr 2019 16:11:44 -0700
> >> >
> >> > On Tue, 16 Apr 2019 at 15:36, Jaime Caamaño Ruiz <jcaamano at suse.de>
> >> > wrote:
> >> > >
> >> > > > On any given system, I would expect ovsdb-server to run as the
> >> > > > same
> >> > > > user
> >> > > > every time.  Is there a reason to sometimes use a different
> >> > > > user?
> >> > >
> >> > > Well, changing from root which was the only supported option in
> >> > > the
> >> > > past and current default to a different user (like the suggested
> >> > > openvswitch), this one time, might be somewhat common. And the
> >> > > scenario
> >> > > that I am looking at is suporting a pianless upgrade through it.
> >> >
> >> > Actually debian packages still by default use "root" user. Not
> >> > "openvswitch".
> >> >
> >> > Long time ago there was an attempt to change the default user
> >> > across
> >> > all different flavor packages to openvswitch (you can lookup the
> >> > patch
> >> > on mailing list). However, as you noticed upgrades are tricky.
> >> > Hence
> >> > packages built from our debian/rules and rhel/openvswitch.spec.in
> >> > files still use "root" as default user. The packages built with
> >> > rhel/openvswitch-fedora.spec.in are an exception where the user
> >> > indeed
> >> > is "openvswitch". Unless you passed --without libcapng flag to
> >> > rpmbuild invocation. Then the user would still be "root".
> >> >
> >> > Here are the difficulties with automating the change of file
> >> > ownership:
> >> > 1. from which context to change ownership? As chown must be invoked
> >> > from something that runs under root then there is not much choice -
> >> > either package installation time (%post scriptlet) or daemon
> >> > startup
> >> > time (assuming you are not using Systemd's USER= feature in spec
> >> > file)
> >> > or something that admin explicitly has to invoke from bash as
> >> > "root".
> >> > 1.1. if it is package installation time then you can't update user
> >> > gracefully at daemon init time. It will be possible only at
> >> > installation time.
> >> > 1.2. if it is installation time then you can run into weird race
> >> > conditions where some code that was executed under root (as package
> >> > %post scriptlets) or previous instance of OVS that was still
> >> > running
> >> > as root could change ownership back to root for some files and
> >> > cause
> >> > unexpected "permission denied" issues (the patch I mentioned was
> >> > affected with these rare race conditions)
> >> > 2. for which files to change ownership? What happens if Unix domain
> >> > socket file remained on fileystem with "root" permissions when OVS
> >> > was
> >> > abruptly killed? What if someone else put a file under ovs
> >> > directories
> >> > with non-root user - should you blindly chown that too? What if
> >> > %post
> >> > scriptlet that runs under root non-atomically created a file and in
> >> > next line chown() it back - is there a window for race? Should you
> >> > follow directories/symlinks recursively? Changing user for conf.db
> >> > file is not enough...
> >> >
> >> > I am not saying it is impossible to change user gracefully on
> >> > upgrades. I am saying that code may have to be reorganized quite a
> >> > bit
> >> > to eliminate the issues I raised above.
> >> >
> >> > Alternatively, for Centos, RHEL and Fedora one can use SElinux to
> >> > confine processes and leave them running as root (instead of
> >> > running
> >> > them under limited privilege user). I believe on SUSE (and Debian)
> >> > once could use AppArmor to achieve the same results. At least for
> >> > SElinux it was a little bit easier to make upgrade seamless than
> >> > with
> >> > Linux user confinement approach.
> >> >
> >> > >
> >> > > So if that makes sense to you, I will go ahead with the patch.
> >> > >
> >> > > BR
> >> > > Jaime.
> >> > >
> >> > > -----Original Message-----
> >> > > From: Ben Pfaff <blp at ovn.org>
> >> > > To: jcaamano at suse.de
> >> > > Cc: ovs-discuss at openvswitch.org
> >> > > Subject: Re: [ovs-discuss] Handling conf.db ownership on
> >> > > OVS_USER_ID
> >> > > changes
> >> > > Date: Tue, 16 Apr 2019 15:25:24 -0700
> >> > >
> >> > > On Tue, Apr 16, 2019 at 11:32:21PM +0200, Jaime Caamaño Ruiz
> >> > > wrote:
> >> > > > When sysconfig OVS_USER_ID is changed to a different user, it
> >> > > > requires
> >> > > > a manual ownership change of the OVS conf.db database if
> >> > > > existing
> >> > > > or
> >> > > > otherwise ovsdb-server will fail to (re)start. I was wondering
> >> > > > if
> >> > > > I
> >> > > > am
> >> > > > missing any particular reason why this is change of ownership
> >> > > > is
> >> > > > not
> >> > > > automatically being handled through the service unit file as it
> >> > > > is
> >> > > > being done with other items.
> >> > >
> >> > > On any given system, I would expect ovsdb-server to run as the
> >> > > same
> >> > > user
> >> > > every time.  Is there a reason to sometimes use a different user?
> >> > >
> >> > > Or, perhaps you are saying that, just before invoking ovsdb-
> >> > > server,
> >> > > the
> >> > > service unit should chown (or whatever) the database file to the
> >> > > user
> >> > > that it is going to use to invoke ovsdb-server.  That might be
> >> > > reasonable, but no one has thought to do it yet.  Do you want to
> >> > > submit
> >> > > a patch?
> >> > >
> >> > > Thanks,
> >> > >
> >> > > Ben.
> >> > >
> >> > > _______________________________________________
> >> > > discuss mailing list
> >> > > discuss at openvswitch.org
> >> > > https://mail.openvswitch.org/mailman/listinfo/ovs-discuss
> >> >
> >> >
> >>
> >>
> >
> >
> > _______________________________________________
> > discuss mailing list
> > discuss at openvswitch.org
> > https://mail.openvswitch.org/mailman/listinfo/ovs-discuss
> _______________________________________________
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> discuss at openvswitch.org
> https://mail.openvswitch.org/mailman/listinfo/ovs-discuss
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