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Date: Wed, 27 Mar 2019 21:12:02 -0400
From: Richard Guy Briggs <rgb@...hat.com>
To: Ondrej Mosnacek <omosnace@...hat.com>
Cc: nhorman@...driver.com, linux-api@...r.kernel.org,
containers@...ts.linux-foundation.org,
LKML <linux-kernel@...r.kernel.org>,
David Howells <dhowells@...hat.com>,
Linux-Audit Mailing List <linux-audit@...hat.com>,
netfilter-devel@...r.kernel.org,
"Eric W . Biederman" <ebiederm@...ssion.com>,
Simo Sorce <simo@...hat.com>, netdev@...r.kernel.org,
linux-fsdevel@...r.kernel.org, Eric Paris <eparis@...isplace.org>,
"Serge E. Hallyn" <serge@...lyn.com>
Subject: Re: [PATCH ghak90 V5 09/10] audit: add support for containerid to
network namespaces
On 2019-03-27 23:42, Ondrej Mosnacek wrote:
> On Fri, Mar 15, 2019 at 7:35 PM Richard Guy Briggs <rgb@...hat.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@...hat.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@...hat.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
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