Re: [PATCH v2 05/10] pidns: Add a limit on the number of pid namespaces

["Serge E. Hallyn" <serge-A9i7LUbDfNHQT0dZR+AlfA@public.gmane.org>]

Quoting Eric W. Biederman (ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org):
> Signed-off-by: "Eric W. Biederman" <ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org>

Acked-by: Serge Hallyn <serge-A9i7LUbDfNHQT0dZR+AlfA@public.gmane.org>

> ---
>  include/linux/user_namespace.h |  1 +
>  kernel/pid_namespace.c         | 22 ++++++++++++++++++----
>  kernel/user_namespace.c        |  1 +
>  3 files changed, 20 insertions(+), 4 deletions(-)
> 
> diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
> index f74a0facc696..47733637741a 100644
> --- a/include/linux/user_namespace.h
> +++ b/include/linux/user_namespace.h
> @@ -24,6 +24,7 @@ struct uid_gid_map {	/* 64 bytes -- 1 cache line */
>  
>  enum ucounts {
>  	UCOUNT_USER_NAMESPACES,
> +	UCOUNT_PID_NAMESPACES,
>  	UCOUNT_COUNTS,
>  };
>  
> diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c
> index a65ba137fd15..049cc14ae37a 100644
> --- a/kernel/pid_namespace.c
> +++ b/kernel/pid_namespace.c
> @@ -79,6 +79,16 @@ static void proc_cleanup_work(struct work_struct *work)
>  /* MAX_PID_NS_LEVEL is needed for limiting size of 'struct pid' */
>  #define MAX_PID_NS_LEVEL 32
>  
> +static bool inc_pid_namespaces(struct user_namespace *ns)
> +{
> +	return inc_ucount(ns, UCOUNT_PID_NAMESPACES);
> +}
> +
> +static void dec_pid_namespaces(struct user_namespace *ns)
> +{
> +	dec_ucount(ns, UCOUNT_PID_NAMESPACES);
> +}
> +
>  static struct pid_namespace *create_pid_namespace(struct user_namespace *user_ns,
>  	struct pid_namespace *parent_pid_ns)
>  {
> @@ -87,15 +97,16 @@ static struct pid_namespace *create_pid_namespace(struct user_namespace *user_ns
>  	int i;
>  	int err;
>  
> -	if (level > MAX_PID_NS_LEVEL) {
> -		err = -EINVAL;
> +	err = -EINVAL;
> +	if (level > MAX_PID_NS_LEVEL)
> +		goto out;
> +	if (!inc_pid_namespaces(user_ns))
>  		goto out;
> -	}
>  
>  	err = -ENOMEM;
>  	ns = kmem_cache_zalloc(pid_ns_cachep, GFP_KERNEL);
>  	if (ns == NULL)
> -		goto out;
> +		goto out_dec;
>  
>  	ns->pidmap[0].page = kzalloc(PAGE_SIZE, GFP_KERNEL);
>  	if (!ns->pidmap[0].page)
> @@ -129,6 +140,8 @@ out_free_map:
>  	kfree(ns->pidmap[0].page);
>  out_free:
>  	kmem_cache_free(pid_ns_cachep, ns);
> +out_dec:
> +	dec_pid_namespaces(user_ns);
>  out:
>  	return ERR_PTR(err);
>  }
> @@ -146,6 +159,7 @@ static void destroy_pid_namespace(struct pid_namespace *ns)
>  	ns_free_inum(&ns->ns);
>  	for (i = 0; i < PIDMAP_ENTRIES; i++)
>  		kfree(ns->pidmap[i].page);
> +	dec_pid_namespaces(ns->user_ns);
>  	put_user_ns(ns->user_ns);
>  	call_rcu(&ns->rcu, delayed_free_pidns);
>  }
> diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
> index 728d7e4995ff..02a03ead7afc 100644
> --- a/kernel/user_namespace.c
> +++ b/kernel/user_namespace.c
> @@ -77,6 +77,7 @@ static int count_max = COUNT_MAX;
>  	}
>  static struct ctl_table userns_table[] = {
>  	UCOUNT_ENTRY("max_user_namespaces"),
> +	UCOUNT_ENTRY("max_pid_namespaces"),
>  	{ }
>  };
>  #endif /* CONFIG_SYSCTL */
> -- 
> 2.8.3