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Date:   Wed, 27 Mar 2019 21:12:02 -0400
From:   Richard Guy Briggs <rgb@redhat.com>
To:     Ondrej Mosnacek <omosnace@redhat.com>
Cc:     nhorman@tuxdriver.com, linux-api@vger.kernel.org,
        containers@lists.linux-foundation.org,
        LKML <linux-kernel@vger.kernel.org>,
        David Howells <dhowells@redhat.com>,
        Linux-Audit Mailing List <linux-audit@redhat.com>,
        netfilter-devel@vger.kernel.org,
        "Eric W . Biederman" <ebiederm@xmission.com>,
        Simo Sorce <simo@redhat.com>, netdev@vger.kernel.org,
        linux-fsdevel@vger.kernel.org, Eric Paris <eparis@parisplace.org>,
        "Serge E. Hallyn" <serge@hallyn.com>
Subject: Re: [PATCH ghak90 V5 09/10] audit: add support for containerid to
 network namespaces
Message-ID: <20190328011202.6raixwzdimn5b4zk@madcap2.tricolour.ca>
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On 2019-03-27 23:42, Ondrej Mosnacek wrote:
> On Fri, Mar 15, 2019 at 7:35 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/include/linux/audit.h b/include/linux/audit.h
> > index fa19fa408931..70255c2dfb9f 100644
> > --- a/include/linux/audit.h
> > +++ b/include/linux/audit.h
> > @@ -27,6 +27,7 @@
> >  #include <linux/ptrace.h>
> >  #include <linux/namei.h>  /* LOOKUP_* */
> >  #include <uapi/linux/audit.h>
> > +#include <linux/refcount.h>
> >
> >  #define AUDIT_INO_UNSET ((unsigned long)-1)
> >  #define AUDIT_DEV_UNSET ((dev_t)-1)
> > @@ -99,6 +100,13 @@ struct audit_task_info {
> >
> >  extern struct audit_task_info init_struct_audit;
> >
> > +struct audit_contid {
> > +       struct list_head        list;
> > +       u64                     id;
> > +       refcount_t              refcount;
> 
> Hm, since we only ever touch the refcount under a spinlock, I wonder
> if we could just make it a regular unsigned int (we don't need the
> atomicity guarantees). OTOH, refcount_t comes with some extra overflow
> checking, so it's probably better to leave it as is...

Since the update is done using rcu-safe methods, do we even need the
spin_lock?  Neil?  Paul?

> > +       struct rcu_head         rcu;
> > +};
> > +
> >  extern int is_audit_feature_set(int which);
> >
> >  extern int __init audit_register_class(int class, unsigned *list);
> > @@ -202,6 +210,10 @@ static inline u64 audit_get_contid(struct task_struct *tsk)
> >  }
> >
> >  extern void audit_log_contid(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 u32 audit_enabled;
> >  #else /* CONFIG_AUDIT */
> > @@ -271,6 +283,13 @@ static inline u64 audit_get_contid(struct task_struct *tsk)
> >
> >  static inline void audit_log_contid(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)
> > +{ }
> >
> >  #define audit_enabled AUDIT_OFF
> >  #endif /* CONFIG_AUDIT */
> > 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;
> > +       spin_lock(&aunet->contid_list_lock);
> > +       if (!list_empty(contid_list))
> > +               list_for_each_entry_rcu(cont, contid_list, list)
> > +                       if (cont->id == contid) {
> > +                               refcount_inc(&cont->refcount);
> > +                               goto out;
> > +                       }
> > +       cont = kmalloc(sizeof(struct audit_contid), GFP_ATOMIC);
> > +       if (cont) {
> > +               INIT_LIST_HEAD(&cont->list);
> > +               cont->id = contid;
> > +               refcount_set(&cont->refcount, 1);
> > +               list_add_rcu(&cont->list, contid_list);
> > +       }
> > +out:
> > +       spin_unlock(&aunet->contid_list_lock);
> > +}
> > +
> > +void audit_netns_contid_del(struct net *net, u64 contid)
> > +{
> > +       struct audit_net *aunet;
> > +       struct list_head *contid_list;
> > +       struct audit_contid *cont = NULL;
> > +
> > +       if (!net)
> > +               return;
> > +       if (!audit_contid_valid(contid))
> > +               return;
> > +       aunet = net_generic(net, audit_net_id);
> > +       if (!aunet)
> > +               return;
> > +       contid_list = &aunet->contid_list;
> > +       spin_lock(&aunet->contid_list_lock);
> > +       if (!list_empty(contid_list))
> > +               list_for_each_entry_rcu(cont, contid_list, list)
> > +                       if (cont->id == contid) {
> > +                               if (refcount_dec_and_test(&cont->refcount)) {
> > +                                       list_del_rcu(&cont->list);
> > +                                       kfree_rcu(cont, rcu);
> > +                               }
> > +                               break;
> > +                       }
> > +       spin_unlock(&aunet->contid_list_lock);
> > +}
> > +
> > +void audit_switch_task_namespaces(struct nsproxy *ns, struct task_struct *p)
> > +{
> > +       u64 contid = audit_get_contid(p);
> > +       struct nsproxy *new = p->nsproxy;
> > +
> > +       if (!audit_contid_valid(contid))
> > +               return;
> > +       audit_netns_contid_del(ns->net_ns, contid);
> > +       if (new)
> > +               audit_netns_contid_add(new->net_ns, contid);
> > +}
> > +
> >  void audit_panic(const char *message)
> >  {
> >         switch (audit_failure) {
> > @@ -1619,7 +1694,6 @@ static int __net_init audit_net_init(struct net *net)
> >                 .flags  = NL_CFG_F_NONROOT_RECV,
> >                 .groups = AUDIT_NLGRP_MAX,
> >         };
> > -
> >         struct audit_net *aunet = net_generic(net, audit_net_id);
> >
> >         aunet->sk = netlink_kernel_create(net, NETLINK_AUDIT, &cfg);
> > @@ -1628,7 +1702,8 @@ static int __net_init audit_net_init(struct net *net)
> >                 return -ENOMEM;
> >         }
> >         aunet->sk->sk_sndtimeo = MAX_SCHEDULE_TIMEOUT;
> > -
> > +       INIT_LIST_HEAD(&aunet->contid_list);
> > +       spin_lock_init(&aunet->contid_list_lock);
> >         return 0;
> >  }
> >
> > @@ -2380,6 +2455,7 @@ int audit_set_contid(struct task_struct *task, u64 contid)
> >         uid_t uid;
> >         struct tty_struct *tty;
> >         char comm[sizeof(current->comm)];
> > +       struct net *net = task->nsproxy->net_ns;
> >
> >         task_lock(task);
> >         /* Can't set if audit disabled */
> > @@ -2401,8 +2477,12 @@ int audit_set_contid(struct task_struct *task, u64 contid)
> >         else if (!(thread_group_leader(task) && thread_group_empty(task)))
> >                 rc = -EALREADY;
> >         read_unlock(&tasklist_lock);
> > -       if (!rc)
> > +       if (!rc) {
> > +               if (audit_contid_valid(oldcontid))
> > +                       audit_netns_contid_del(net, oldcontid);
> >                 task->audit->contid = contid;
> > +               audit_netns_contid_add(net, contid);
> > +       }
> >         task_unlock(task);
> >
> >         if (!audit_enabled)
> > diff --git a/kernel/nsproxy.c b/kernel/nsproxy.c
> > index f6c5d330059a..718b1201ae70 100644
> > --- a/kernel/nsproxy.c
> > +++ b/kernel/nsproxy.c
> > @@ -27,6 +27,7 @@
> >  #include <linux/syscalls.h>
> >  #include <linux/cgroup.h>
> >  #include <linux/perf_event.h>
> > +#include <linux/audit.h>
> >
> >  static struct kmem_cache *nsproxy_cachep;
> >
> > @@ -140,6 +141,7 @@ int copy_namespaces(unsigned long flags, struct task_struct *tsk)
> >         struct nsproxy *old_ns = tsk->nsproxy;
> >         struct user_namespace *user_ns = task_cred_xxx(tsk, user_ns);
> >         struct nsproxy *new_ns;
> > +       u64 contid = audit_get_contid(tsk);
> >
> >         if (likely(!(flags & (CLONE_NEWNS | CLONE_NEWUTS | CLONE_NEWIPC |
> >                               CLONE_NEWPID | CLONE_NEWNET |
> > @@ -167,6 +169,7 @@ int copy_namespaces(unsigned long flags, struct task_struct *tsk)
> >                 return  PTR_ERR(new_ns);
> >
> >         tsk->nsproxy = new_ns;
> > +       audit_netns_contid_add(new_ns->net_ns, contid);
> >         return 0;
> >  }
> >
> > @@ -224,6 +227,7 @@ void switch_task_namespaces(struct task_struct *p, struct nsproxy *new)
> >         ns = p->nsproxy;
> >         p->nsproxy = new;
> >         task_unlock(p);
> > +       audit_switch_task_namespaces(ns, p);
> 
> Since we call audit_switch_task_namespaces() after task_unlock(),
> could there be a potential race condition? I'm not going to dive too
> much into this now, because it's getting late here, but on first look
> it seems like p->nsproxy could change under our hands before we fetch
> it in audit_switch_task_namespaces()...

The rules are defined in include/linux/nsproxy.h.

Since the callers (sys_setns, do_exit, copy_process error path) are all
current or handing it a dead task and we are not writing nsproxy or its
pointers, which is only allowed by current anyway, we don't need the
lock.

> >
> >         if (ns && atomic_dec_and_test(&ns->count))
> >                 free_nsproxy(ns);
> > --
> > 1.8.3.1
> 
> Ondrej Mosnacek <omosnace at redhat dot com>

- RGB

--
Richard Guy Briggs <rgb@redhat.com>
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