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Date:   Tue, 2 Apr 2019 10:28:39 -0400
From:   Neil Horman <nhorman@tuxdriver.com>
To:     Paul Moore <paul@paul-moore.com>
Cc:     Richard Guy Briggs <rgb@redhat.com>,
        containers@lists.linux-foundation.org, linux-api@vger.kernel.org,
        Linux-Audit Mailing List <linux-audit@redhat.com>,
        linux-fsdevel@vger.kernel.org, LKML <linux-kernel@vger.kernel.org>,
        netdev@vger.kernel.org, netfilter-devel@vger.kernel.org,
        sgrubb@redhat.com, omosnace@redhat.com, dhowells@redhat.com,
        simo@redhat.com, Eric Paris <eparis@parisplace.org>,
        Serge Hallyn <serge@hallyn.com>, ebiederm@xmission.com
Subject: Re: [PATCH ghak90 V5 09/10] audit: add support for containerid to
 network namespaces
Message-ID: <20190402142839.GC17593@hmswarspite.think-freely.org>
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On Tue, Apr 02, 2019 at 09:31:49AM -0400, Paul Moore wrote:
> On Tue, Apr 2, 2019 at 7:32 AM Neil Horman <nhorman@tuxdriver.com> wrote:
> > On Mon, Apr 01, 2019 at 10:50:03AM -0400, Paul Moore wrote:
> > > On Fri, Mar 15, 2019 at 2:35 PM Richard Guy Briggs <rgb@redhat.com> wrote:
> > > > Audit events could happen in a network namespace outside of a task
> > > > context due to packets received from the net that trigger an auditing
> > > > rule prior to being associated with a running task.  The network
> > > > namespace could be in use by multiple containers by association to the
> > > > tasks in that network namespace.  We still want a way to attribute
> > > > these events to any potential containers.  Keep a list per network
> > > > namespace to track these audit container identifiiers.
> > > >
> > > > Add/increment the audit container identifier on:
> > > > - initial setting of the audit container identifier via /proc
> > > > - clone/fork call that inherits an audit container identifier
> > > > - unshare call that inherits an audit container identifier
> > > > - setns call that inherits an audit container identifier
> > > > Delete/decrement the audit container identifier on:
> > > > - an inherited audit container identifier dropped when child set
> > > > - process exit
> > > > - unshare call that drops a net namespace
> > > > - setns call that drops a net namespace
> > > >
> > > > See: https://github.com/linux-audit/audit-kernel/issues/92
> > > > See: https://github.com/linux-audit/audit-testsuite/issues/64
> > > > See: https://github.com/linux-audit/audit-kernel/wiki/RFE-Audit-Container-ID
> > > > Signed-off-by: Richard Guy Briggs <rgb@redhat.com>
> > > > ---
> > > >  include/linux/audit.h | 19 ++++++++++++
> > > >  kernel/audit.c        | 86 +++++++++++++++++++++++++++++++++++++++++++++++++--
> > > >  kernel/nsproxy.c      |  4 +++
> > > >  3 files changed, 106 insertions(+), 3 deletions(-)
> > >
> > > ...
> > >
> > > > diff --git a/kernel/audit.c b/kernel/audit.c
> > > > index cf448599ef34..7fa3194f5342 100644
> > > > --- a/kernel/audit.c
> > > > +++ b/kernel/audit.c
> > > > @@ -72,6 +72,7 @@
> > > >  #include <linux/freezer.h>
> > > >  #include <linux/pid_namespace.h>
> > > >  #include <net/netns/generic.h>
> > > > +#include <net/net_namespace.h>
> > > >
> > > >  #include "audit.h"
> > > >
> > > > @@ -99,9 +100,13 @@
> > > >  /**
> > > >   * struct audit_net - audit private network namespace data
> > > >   * @sk: communication socket
> > > > + * @contid_list: audit container identifier list
> > > > + * @contid_list_lock audit container identifier list lock
> > > >   */
> > > >  struct audit_net {
> > > >         struct sock *sk;
> > > > +       struct list_head contid_list;
> > > > +       spinlock_t contid_list_lock;
> > > >  };
> > > >
> > > >  /**
> > > > @@ -275,8 +280,11 @@ struct audit_task_info init_struct_audit = {
> > > >  void audit_free(struct task_struct *tsk)
> > > >  {
> > > >         struct audit_task_info *info = tsk->audit;
> > > > +       struct nsproxy *ns = tsk->nsproxy;
> > > >
> > > >         audit_free_syscall(tsk);
> > > > +       if (ns)
> > > > +               audit_netns_contid_del(ns->net_ns, audit_get_contid(tsk));
> > > >         /* Freeing the audit_task_info struct must be performed after
> > > >          * audit_log_exit() due to need for loginuid and sessionid.
> > > >          */
> > > > @@ -376,6 +384,73 @@ static struct sock *audit_get_sk(const struct net *net)
> > > >         return aunet->sk;
> > > >  }
> > > >
> > > > +void audit_netns_contid_add(struct net *net, u64 contid)
> > > > +{
> > > > +       struct audit_net *aunet = net_generic(net, audit_net_id);
> > > > +       struct list_head *contid_list = &aunet->contid_list;
> > > > +       struct audit_contid *cont;
> > > > +
> > > > +       if (!audit_contid_valid(contid))
> > > > +               return;
> > > > +       if (!aunet)
> > > > +               return;
> > >
> > > We should move the contid_list assignment below this check, or decide
> > > that aunet is always going to valid (?) and get rid of this check
> > > completely.
> > >
> > I'm not sure why that would be needed.  Finding the net_id list is an operation
> > of a map relating net namespaces to lists, not contids to lists.  We could do
> > it, sure, but since they're unrelated operations, I don't think we experience
> > any slowdowns from doing it this way.
> 
> In the first line of the function, when aunet is declared, it is also
> assigned a value using net_generic():
> 
>   struct audit_net *aunet = net_generic(net, audit_net_id);
> 
> Later in the function there is check to see if aunet is NULL, yet on
> the second line of the function (before the NULL check), there is this
> line of code:
> 
>   struct list_head *contid_list = &aunet->contid_list;
> 
> ... which could result in the dereference of a NULL pointer if aunet
> is NULL.  My suggestion was either to move this assignment below the
> aunet-NULL check or decide that aunet was always going to be valid
> (e.g. non-NULL) and do away with the aunet-NULL check completely.
> Richard has since replied that the aunet-NULL check has been
> demonstrated to be necessary so the proper thing to do would be to
> move the assignment.  I believe that is what Richard is planning on
> doing.
> 
oh, I'm sorry, you're right, I was looking at the contid tests not the list
tests.

Neil

> > > > +       if (cont) {
> > > > +               INIT_LIST_HEAD(&cont->list);
> > >
> > > Unless there is some guidance that INIT_LIST_HEAD() should be used
> > > regardless, you shouldn't need to call this here since list_add_rcu()
> > > will take care of any list.h related initialization.
> >
> > There is a corner case that needs it.  list_add_rcu has a check that gets
> > called, __list_add_valid.  Its a noop in the regular case, but if
> > CONFIG_DEBUG_LIST is defined, its a check to ensure that the next and prev
> > pointers getting passed in aren't set to detectable corrupt values.  If we pass
> > in garbage, we can get transient false positives on that check, so we need to
> > set the list pointers to known good values before hand, either by using kzalloc,
> > or INIT_LIST_HEAD, as has been done here.  Given that we expressly set every
> > field of this structure, I think this is the right approach, as it uses the list
> > macro to expressly set the list values to their proper state.
> 
> Good to know, thanks.
> 
> -- 
> paul moore
> www.paul-moore.com
>