linux-kernel - Re: [PATCH v2 06/10] utsns: Add a limit on the number of uts namespaces

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Message-ID: <20160725230927.GD26841@mail.hallyn.com>
Date:	Mon, 25 Jul 2016 18:09:28 -0500
From:	"Serge E. Hallyn" <serge@...lyn.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Linux Containers <containers@...ts.linux-foundation.org>,
	Andy Lutomirski <luto@...capital.net>,
	Jann Horn <jann@...jh.net>, Kees Cook <keescook@...omium.org>,
	Nikolay Borisov <kernel@...p.com>,
	"Serge E. Hallyn" <serge@...lyn.com>,
	Seth Forshee <seth.forshee@...onical.com>,
	linux-fsdevel@...r.kernel.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-api@...r.kernel.org
Subject: Re: [PATCH v2 06/10] utsns: Add a limit on the number of uts
 namespaces

Quoting Eric W. Biederman (ebiederm@...ssion.com):
> Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>

Acked-by: Serge Hallyn <serge@...lyn.com>

> ---
>  include/linux/user_namespace.h |  1 +
>  kernel/user_namespace.c        |  1 +
>  kernel/utsname.c               | 31 ++++++++++++++++++++++++++-----
>  3 files changed, 28 insertions(+), 5 deletions(-)
> 
> diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
> index 47733637741a..bed2506081fe 100644
> --- a/include/linux/user_namespace.h
> +++ b/include/linux/user_namespace.h
> @@ -25,6 +25,7 @@ struct uid_gid_map {	/* 64 bytes -- 1 cache line */
>  enum ucounts {
>  	UCOUNT_USER_NAMESPACES,
>  	UCOUNT_PID_NAMESPACES,
> +	UCOUNT_UTS_NAMESPACES,
>  	UCOUNT_COUNTS,
>  };
>  
> diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
> index 02a03ead7afc..6b205c24e888 100644
> --- a/kernel/user_namespace.c
> +++ b/kernel/user_namespace.c
> @@ -78,6 +78,7 @@ static int count_max = COUNT_MAX;
>  static struct ctl_table userns_table[] = {
>  	UCOUNT_ENTRY("max_user_namespaces"),
>  	UCOUNT_ENTRY("max_pid_namespaces"),
> +	UCOUNT_ENTRY("max_uts_namespaces"),
>  	{ }
>  };
>  #endif /* CONFIG_SYSCTL */
> diff --git a/kernel/utsname.c b/kernel/utsname.c
> index 831ea7108232..4f13c0419d64 100644
> --- a/kernel/utsname.c
> +++ b/kernel/utsname.c
> @@ -17,6 +17,16 @@
>  #include <linux/user_namespace.h>
>  #include <linux/proc_ns.h>
>  
> +static bool inc_uts_namespaces(struct user_namespace *ns)
> +{
> +	return inc_ucount(ns, UCOUNT_UTS_NAMESPACES);
> +}
> +
> +static void dec_uts_namespaces(struct user_namespace *ns)
> +{
> +	dec_ucount(ns, UCOUNT_UTS_NAMESPACES);
> +}
> +
>  static struct uts_namespace *create_uts_ns(void)
>  {
>  	struct uts_namespace *uts_ns;
> @@ -38,15 +48,18 @@ static struct uts_namespace *clone_uts_ns(struct user_namespace *user_ns,
>  	struct uts_namespace *ns;
>  	int err;
>  
> +	err = -ENFILE;
> +	if (!inc_uts_namespaces(user_ns))
> +		goto fail;
> +
> +	err = -ENOMEM;
>  	ns = create_uts_ns();
>  	if (!ns)
> -		return ERR_PTR(-ENOMEM);
> +		goto fail_dec;
>  
>  	err = ns_alloc_inum(&ns->ns);
> -	if (err) {
> -		kfree(ns);
> -		return ERR_PTR(err);
> -	}
> +	if (err)
> +		goto fail_free;
>  
>  	ns->ns.ops = &utsns_operations;
>  
> @@ -55,6 +68,13 @@ static struct uts_namespace *clone_uts_ns(struct user_namespace *user_ns,
>  	ns->user_ns = get_user_ns(user_ns);
>  	up_read(&uts_sem);
>  	return ns;
> +
> +fail_free:
> +	kfree(ns);
> +fail_dec:
> +	dec_uts_namespaces(user_ns);
> +fail:
> +	return ERR_PTR(err);
>  }
>  
>  /*
> @@ -85,6 +105,7 @@ void free_uts_ns(struct kref *kref)
>  	struct uts_namespace *ns;
>  
>  	ns = container_of(kref, struct uts_namespace, kref);
> +	dec_uts_namespaces(ns->user_ns);
>  	put_user_ns(ns->user_ns);
>  	ns_free_inum(&ns->ns);
>  	kfree(ns);
> -- 
> 2.8.3