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[PATCH v2 09/10] netns: Add a limit on the number of net namespaces

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  [PATCH v2 09/10] netns: Add a limit on the number of net namespaces "Eric W. Biederman" <ebiederm@xmission.com> - 2016-07-21 19:00 +0200
    Re: [PATCH v2 09/10] netns: Add a limit on the number of net namespaces Andrei Vagin <avagin@gmail.com> - 2016-07-26 08:10 +0200
      Re: [PATCH v2 09/10] netns: Add a limit on the number of net namespaces ebiederm@xmission.com (Eric W. Biederman) - 2016-07-26 22:20 +0200

#1448008 — [PATCH v2 09/10] netns: Add a limit on the number of net namespaces

Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
---
 include/linux/user_namespace.h |  1 +
 kernel/user_namespace.c        |  1 +
 net/core/net_namespace.c       | 15 +++++++++++++++
 3 files changed, 17 insertions(+)

diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
index 1a3a9cb93277..f86afa536baf 100644
--- a/include/linux/user_namespace.h
+++ b/include/linux/user_namespace.h
@@ -27,6 +27,7 @@ enum ucounts {
 	UCOUNT_PID_NAMESPACES,
 	UCOUNT_UTS_NAMESPACES,
 	UCOUNT_IPC_NAMESPACES,
+	UCOUNT_NET_NAMESPACES,
 	UCOUNT_CGROUP_NAMESPACES,
 	UCOUNT_COUNTS,
 };
diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
index 1cf074cb47e2..e326ca722ae0 100644
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -80,6 +80,7 @@ static struct ctl_table userns_table[] = {
 	UCOUNT_ENTRY("max_pid_namespaces"),
 	UCOUNT_ENTRY("max_uts_namespaces"),
 	UCOUNT_ENTRY("max_ipc_namespaces"),
+	UCOUNT_ENTRY("max_net_namespaces"),
 	UCOUNT_ENTRY("max_cgroup_namespaces"),
 	{ }
 };
diff --git a/net/core/net_namespace.c b/net/core/net_namespace.c
index 2c2eb1b629b1..a489f192d619 100644
--- a/net/core/net_namespace.c
+++ b/net/core/net_namespace.c
@@ -266,6 +266,16 @@ struct net *get_net_ns_by_id(struct net *net, int id)
 	return peer;
 }
 
+static bool inc_net_namespaces(struct user_namespace *ns)
+{
+	return inc_ucount(ns, UCOUNT_NET_NAMESPACES);
+}
+
+static void dec_net_namespaces(struct user_namespace *ns)
+{
+	dec_ucount(ns, UCOUNT_NET_NAMESPACES);
+}
+
 /*
  * setup_net runs the initializers for the network namespace object.
  */
@@ -276,6 +286,9 @@ static __net_init int setup_net(struct net *net, struct user_namespace *user_ns)
 	int error = 0;
 	LIST_HEAD(net_exit_list);
 
+	if (!inc_net_namespaces(user_ns))
+		return -ENFILE;
+
 	atomic_set(&net->count, 1);
 	atomic_set(&net->passive, 1);
 	net->dev_base_seq = 1;
@@ -372,6 +385,7 @@ struct net *copy_net_ns(unsigned long flags,
 	}
 	mutex_unlock(&net_mutex);
 	if (rv < 0) {
+		dec_net_namespaces(user_ns);
 		put_user_ns(user_ns);
 		net_drop_ns(net);
 		return ERR_PTR(rv);
@@ -444,6 +458,7 @@ static void cleanup_net(struct work_struct *work)
 	/* Finally it is safe to free my network namespace structure */
 	list_for_each_entry_safe(net, tmp, &net_exit_list, exit_list) {
 		list_del_init(&net->exit_list);
+		dec_net_namespaces(net->user_ns);
 		put_user_ns(net->user_ns);
 		net_drop_ns(net);
 	}
-- 
2.8.3

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#1450388

On Thu, Jul 21, 2016 at 9:40 AM, Eric W. Biederman
<ebiederm@xmission.com> wrote:
> Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
> ---
>  include/linux/user_namespace.h |  1 +
>  kernel/user_namespace.c        |  1 +
>  net/core/net_namespace.c       | 15 +++++++++++++++
>  3 files changed, 17 insertions(+)
>
> diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
> index 1a3a9cb93277..f86afa536baf 100644
> --- a/include/linux/user_namespace.h
> +++ b/include/linux/user_namespace.h
> @@ -27,6 +27,7 @@ enum ucounts {
>         UCOUNT_PID_NAMESPACES,
>         UCOUNT_UTS_NAMESPACES,
>         UCOUNT_IPC_NAMESPACES,
> +       UCOUNT_NET_NAMESPACES,
>         UCOUNT_CGROUP_NAMESPACES,
>         UCOUNT_COUNTS,
>  };
> diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
> index 1cf074cb47e2..e326ca722ae0 100644
> --- a/kernel/user_namespace.c
> +++ b/kernel/user_namespace.c
> @@ -80,6 +80,7 @@ static struct ctl_table userns_table[] = {
>         UCOUNT_ENTRY("max_pid_namespaces"),
>         UCOUNT_ENTRY("max_uts_namespaces"),
>         UCOUNT_ENTRY("max_ipc_namespaces"),
> +       UCOUNT_ENTRY("max_net_namespaces"),
>         UCOUNT_ENTRY("max_cgroup_namespaces"),
>         { }
>  };
> diff --git a/net/core/net_namespace.c b/net/core/net_namespace.c
> index 2c2eb1b629b1..a489f192d619 100644
> --- a/net/core/net_namespace.c
> +++ b/net/core/net_namespace.c
> @@ -266,6 +266,16 @@ struct net *get_net_ns_by_id(struct net *net, int id)
>         return peer;
>  }
>
> +static bool inc_net_namespaces(struct user_namespace *ns)
> +{
> +       return inc_ucount(ns, UCOUNT_NET_NAMESPACES);
> +}
> +
> +static void dec_net_namespaces(struct user_namespace *ns)
> +{
> +       dec_ucount(ns, UCOUNT_NET_NAMESPACES);
> +}
> +
>  /*
>   * setup_net runs the initializers for the network namespace object.
>   */
> @@ -276,6 +286,9 @@ static __net_init int setup_net(struct net *net, struct user_namespace *user_ns)
>         int error = 0;
>         LIST_HEAD(net_exit_list);
>
> +       if (!inc_net_namespaces(user_ns))
> +               return -ENFILE;

I think you need to move this check after initilizing  net->passive.
When setup_net returns an error, net_drop_ns is called:

void net_drop_ns(void *p)
{
        struct net *ns = p;
        if (ns && atomic_dec_and_test(&ns->passive))
                net_free(ns);
}

Actually, I think it would be better to make this check before net_alloc().

> +
>         atomic_set(&net->count, 1);
>         atomic_set(&net->passive, 1);
>         net->dev_base_seq = 1;
> @@ -372,6 +385,7 @@ struct net *copy_net_ns(unsigned long flags,
>         }
>         mutex_unlock(&net_mutex);
>         if (rv < 0) {
> +               dec_net_namespaces(user_ns);
>                 put_user_ns(user_ns);
>                 net_drop_ns(net);
>                 return ERR_PTR(rv);
> @@ -444,6 +458,7 @@ static void cleanup_net(struct work_struct *work)
>         /* Finally it is safe to free my network namespace structure */
>         list_for_each_entry_safe(net, tmp, &net_exit_list, exit_list) {
>                 list_del_init(&net->exit_list);
> +               dec_net_namespaces(net->user_ns);
>                 put_user_ns(net->user_ns);
>                 net_drop_ns(net);
>         }
> --
> 2.8.3
>
> _______________________________________________
> Containers mailing list
> Containers@lists.linux-foundation.org
> https://lists.linuxfoundation.org/mailman/listinfo/containers

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#1450837

Andrei Vagin <avagin@gmail.com> writes:

> On Thu, Jul 21, 2016 at 9:40 AM, Eric W. Biederman <ebiederm@xmission.com> wrote:
>> index 2c2eb1b629b1..a489f192d619 100644
>> --- a/net/core/net_namespace.c
>> +++ b/net/core/net_namespace.c
>> @@ -266,6 +266,16 @@ struct net *get_net_ns_by_id(struct net *net, int id)
>>         return peer;
>>  }
>>
>> +static bool inc_net_namespaces(struct user_namespace *ns)
>> +{
>> +       return inc_ucount(ns, UCOUNT_NET_NAMESPACES);
>> +}
>> +
>> +static void dec_net_namespaces(struct user_namespace *ns)
>> +{
>> +       dec_ucount(ns, UCOUNT_NET_NAMESPACES);
>> +}
>> +
>>  /*
>>   * setup_net runs the initializers for the network namespace object.
>>   */
>> @@ -276,6 +286,9 @@ static __net_init int setup_net(struct net *net, struct user_namespace *user_ns)
>>         int error = 0;
>>         LIST_HEAD(net_exit_list);
>>
>> +       if (!inc_net_namespaces(user_ns))
>> +               return -ENFILE;
>
> I think you need to move this check after initilizing  net->passive.
> When setup_net returns an error, net_drop_ns is called:
>
Good point.  Ouch!

> void net_drop_ns(void *p)
> {
>         struct net *ns = p;
>         if (ns && atomic_dec_and_test(&ns->passive))
>                 net_free(ns);
> }
>
> Actually, I think it would be better to make this check before
> net_alloc().

You are probably right.  I seem to be trying to be entirely too clever
putting that in setup_net so I can cover the initial network namespace.
Which really does not need to be counted.  As clearly I also goofed up
the decrement on error case as well.

Eric

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