Re: [PATCH ghak90 V8 11/16] audit: add support for containerid to network namespaces

[Richard Guy Briggs]

On 2020-01-22 16:28, Paul Moore wrote:
> On Tue, Dec 31, 2019 at 2:51 PM Richard Guy Briggs <rgb@xxxxxxxxxx> wrote:
> >
> > This also adds support to qualify NETFILTER_PKT records.
> >
> > 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
> >
> > Add audit container identifier auxiliary record(s) to NETFILTER_PKT
> > event standalone records.  Iterate through all potential audit container
> > identifiers associated with a network namespace.
> >
> > Please see the github audit kernel issue for contid net support:
> >   https://github.com/linux-audit/audit-kernel/issues/92
> > Please see the github audit testsuiite issue for the test case:
> >   https://github.com/linux-audit/audit-testsuite/issues/64
> > Please see the github audit wiki for the feature overview:
> >   https://github.com/linux-audit/audit-kernel/wiki/RFE-Audit-Container-ID
> > Signed-off-by: Richard Guy Briggs <rgb@xxxxxxxxxx>
> > Acked-by: Neil Horman <nhorman@xxxxxxxxxxxxx>
> > Reviewed-by: Ondrej Mosnacek <omosnace@xxxxxxxxxx>
> > ---
> >  include/linux/audit.h    |  24 +++++++++
> >  kernel/audit.c           | 132 ++++++++++++++++++++++++++++++++++++++++++++++-
> >  kernel/nsproxy.c         |   4 ++
> >  net/netfilter/nft_log.c  |  11 +++-
> >  net/netfilter/xt_AUDIT.c |  11 +++-
> >  5 files changed, 176 insertions(+), 6 deletions(-)
> 
> ...
> 
> > diff --git a/include/linux/audit.h b/include/linux/audit.h
> > index 5531d37a4226..ed8d5b74758d 100644
> > --- a/include/linux/audit.h
> > +++ b/include/linux/audit.h
> > @@ -12,6 +12,7 @@
> >  #include <linux/sched.h>
> >  #include <linux/ptrace.h>
> >  #include <uapi/linux/audit.h>
> > +#include <linux/refcount.h>
> >
> >  #define AUDIT_INO_UNSET ((unsigned long)-1)
> >  #define AUDIT_DEV_UNSET ((dev_t)-1)
> > @@ -121,6 +122,13 @@ struct audit_task_info {
> >
> >  extern struct audit_task_info init_struct_audit;
> >
> > +struct audit_contobj_netns {
> > +       struct list_head        list;
> > +       u64                     id;
> 
> Since we now track audit container IDs in their own structure, why not
> link directly to the audit container ID object (and bump the
> refcount)?

Ok, I've done this but at first I had doubts about the complexity.

> > +       refcount_t              refcount;
> > +       struct rcu_head         rcu;
> > +};
> > +
> >  extern int is_audit_feature_set(int which);
> >
> >  extern int __init audit_register_class(int class, unsigned *list);
> > @@ -225,6 +233,12 @@ static inline u64 audit_get_contid(struct task_struct *tsk)
> >  }
> >
> >  extern void audit_log_container_id(struct audit_context *context, u64 contid);
> > +extern void audit_netns_contid_add(struct net *net, u64 contid);
> > +extern void audit_netns_contid_del(struct net *net, u64 contid);
> > +extern void audit_switch_task_namespaces(struct nsproxy *ns,
> > +                                        struct task_struct *p);
> > +extern void audit_log_netns_contid_list(struct net *net,
> > +                                       struct audit_context *context);
> >
> >  extern u32 audit_enabled;
> >
> > @@ -297,6 +311,16 @@ static inline u64 audit_get_contid(struct task_struct *tsk)
> >
> >  static inline void audit_log_container_id(struct audit_context *context, u64 contid)
> >  { }
> > +static inline void audit_netns_contid_add(struct net *net, u64 contid)
> > +{ }
> > +static inline void audit_netns_contid_del(struct net *net, u64 contid)
> > +{ }
> > +static inline void audit_switch_task_namespaces(struct nsproxy *ns,
> > +                                               struct task_struct *p)
> > +{ }
> > +static inline void audit_log_netns_contid_list(struct net *net,
> > +                                              struct audit_context *context)
> > +{ }
> >
> >  #define audit_enabled AUDIT_OFF
> >
> > diff --git a/kernel/audit.c b/kernel/audit.c
> > index d4e6eafe5644..f7a8d3288ca0 100644
> > --- a/kernel/audit.c
> > +++ b/kernel/audit.c
> > @@ -59,6 +59,7 @@
> >  #include <linux/freezer.h>
> >  #include <linux/pid_namespace.h>
> >  #include <net/netns/generic.h>
> > +#include <net/net_namespace.h>
> >
> >  #include "audit.h"
> >
> > @@ -86,9 +87,13 @@
> >  /**
> >   * 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;
> >  };
> >
> >  /**
> > @@ -305,8 +310,11 @@ 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.
> >          */
> > @@ -409,6 +417,120 @@ 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;
> > +       struct list_head *contid_list;
> > +       struct audit_contobj_netns *cont;
> > +
> > +       if (!net)
> > +               return;
> > +       if (!audit_contid_valid(contid))
> > +               return;
> > +       aunet = net_generic(net, audit_net_id);
> > +       if (!aunet)
> > +               return;
> > +       contid_list = &aunet->contid_list;
> > +       rcu_read_lock();
> > +       list_for_each_entry_rcu(cont, contid_list, list)
> > +               if (cont->id == contid) {
> > +                       spin_lock(&aunet->contid_list_lock);
> > +                       refcount_inc(&cont->refcount);
> > +                       spin_unlock(&aunet->contid_list_lock);
> > +                       goto out;
> > +               }
> > +       cont = kmalloc(sizeof(*cont), GFP_ATOMIC);
> > +       if (cont) {
> > +               INIT_LIST_HEAD(&cont->list);
> > +               cont->id = contid;
> > +               refcount_set(&cont->refcount, 1);
> > +               spin_lock(&aunet->contid_list_lock);
> > +               list_add_rcu(&cont->list, contid_list);
> > +               spin_unlock(&aunet->contid_list_lock);
> > +       }
> > +out:
> > +       rcu_read_unlock();
> > +}
> 
> See my comments about refcount_t, spinlocks, and list manipulation
> races from earlier in the patchset; the same thing applies to the
> function above.

This was some of the complexity that concerned me, but switching to rcu
read locks helped.  In this case, since a stale list would cause an
update issue and these counts aren't used or updated anywere else,
switching to an int makes sense.

> paul moore

- RGB

--
Richard Guy Briggs <rgb@xxxxxxxxxx>
Sr. S/W Engineer, Kernel Security, Base Operating Systems
Remote, Ottawa, Red Hat Canada
IRC: rgb, SunRaycer
Voice: +1.647.777.2635, Internal: (81) 32635