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Message-ID: <CAHC9VhQpk6cFZckQH+LQmQmirVzLm_GH57ZD3-76y-59G=DocQ@mail.gmail.com>
Date: Mon, 1 Apr 2019 10:50:03 -0400
From: Paul Moore <paul@...l-moore.com>
To: Richard Guy Briggs <rgb@...hat.com>
Cc: containers@...ts.linux-foundation.org, linux-api@...r.kernel.org,
Linux-Audit Mailing List <linux-audit@...hat.com>,
linux-fsdevel@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
netdev@...r.kernel.org, netfilter-devel@...r.kernel.org,
sgrubb@...hat.com, omosnace@...hat.com, dhowells@...hat.com,
simo@...hat.com, Eric Paris <eparis@...isplace.org>,
Serge Hallyn <serge@...lyn.com>, ebiederm@...ssion.com,
nhorman@...driver.com
Subject: Re: [PATCH ghak90 V5 09/10] audit: add support for containerid to
network namespaces
On Fri, Mar 15, 2019 at 2:35 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/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;
We should move the contid_list assignment below this check, or decide
that aunet is always going to valid (?) and get rid of this check
completely.
> + spin_lock(&aunet->contid_list_lock);
> + if (!list_empty(contid_list))
We don't need the list_empty() check here do we? I think we can just
call list_for_each_entry_rcu(), yes?
> + 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 you had to guess, what do you think is going to be more common:
bumping the refcount of an existing entry in the list, or adding a new
entry? I'm asking because I always get a little nervous when doing
allocations while holding a spinlock. Yes, you are doing it with
GFP_ATOMIC, but it still seems like something to try and avoid if this
is going to approach 50%. However, if the new entry is rare then the
extra work of always doing the allocation before taking the lock and
then freeing it afterwards might be a bad tradeoff.
My gut feeling says we might do about as many allocations as refcount
bumps, but I could be thinking about this wrong.
Moving the allocation outside the spinlock might also open the door to
doing this as GFP_KERNEL, which is a good thing, but I haven't looked
at the callers to see if that is possible (it may not be). That's an
exercise left to the patch author (if he hasn't done that already).
> + if (cont) {
> + INIT_LIST_HEAD(&cont->list);
Unless there is some guidance that INIT_LIST_HEAD() should be used
regardless, you shouldn't need to call this here since list_add_rcu()
will take care of any list.h related initialization.
> + cont->id = contid;
> + refcount_set(&cont->refcount, 1);
> + list_add_rcu(&cont->list, contid_list);
> + }
> +out:
> + spin_unlock(&aunet->contid_list_lock);
> +}
--
paul moore
www.paul-moore.com
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