On 2019-03-27 23:42, Ondrej Mosnacek wrote:

On Fri, Mar 15, 2019 at 7:35 PM Richard Guy Briggs [off-list ref] wrote:

quoted

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 <redacted>
---
 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?

quoted

+       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.

quoted

        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 [off-list ref]
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