linux-kernel - Re: [RFC PATCH] cgroup namespaces: add a 'nsroot=' mountinfo field

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Message-ID: <20160413175736.GC3676@htj.duckdns.org>
Date:	Wed, 13 Apr 2016 13:57:36 -0400
From:	Tejun Heo <tj@...nel.org>
To:	"Serge E. Hallyn" <serge@...lyn.com>
Cc:	linux-api@...r.kernel.org, adityakali@...gle.com,
	Linux Containers <containers@...ts.osdl.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	cgroups@...r.kernel.org, lkml <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH] cgroup namespaces: add a 'nsroot=' mountinfo field

Hello, Serge.

Sorry about the delay.

On Mon, Mar 21, 2016 at 06:41:33PM -0500, Serge E. Hallyn wrote:
>  struct kernfs_syscall_ops {
>  	int (*remount_fs)(struct kernfs_root *root, int *flags, char *data);
> -	int (*show_options)(struct seq_file *sf, struct kernfs_root *root);
> +	int (*show_options)(struct seq_file *sf, struct dentry *dentry,
> +			    struct kernfs_root *root);

Wouldn't it make more sense to pass in kernfs_node pointer instead of
dentry pointer?

> +static void cgroup_show_nsroot(struct seq_file *seq, struct dentry *dentry,
> +			       struct kernfs_root *kf_root)
> +{
> +	struct kernfs_node *d_kn = dentry->d_fsdata;
> +	char *nsroot;
> +	int len, ret;
> +
> +	if (!kf_root)
> +		return;
> +	len = kernfs_path_from_node(d_kn, kf_root->kn, NULL, 0);
> +	if (len <= 0)
> +		return;
> +	nsroot = kzalloc(len + 1, GFP_ATOMIC);
> +	if (!nsroot)
> +		return;
> +	ret = kernfs_path_from_node(d_kn, kf_root->kn, nsroot, len + 1);
> +	if (ret <= 0 || ret > len)
> +		goto out;

Hmmm.... does this mean that someone inside cgroup ns would be able to
find out the absolute cgroup path of the ns root from inside?  If so,
wouldn't that be an unnecessary information leak?

Thanks.

-- 
tejun