Re: [PATCH ghak90 V5 09/10] audit: add support for containerid to network namespaces

[Ondrej Mosnacek <omosnace@redhat.com>]

On Thu, Mar 28, 2019 at 2:12 AM Richard Guy Briggs <rgb@redhat.com> wrote:
> 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.

I see, so the task lock is taken during the swap only to protect
against races with other tasks reading this task's nsproxy... makes
sense. Thanks for clarifying!

The refcount/spinlock issue is not blocking (and could be addressed in
a follow-up patch later), so:

Reviewed-by: Ondrej Mosnacek <omosnace@redhat.com>

>
> > >
> > >         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

--
Ondrej Mosnacek <omosnace at redhat dot com>
Software Engineer, Security Technologies
Red Hat, Inc.