linux-kernel - Re: [RFC PATCH 3/8] kmod - teach call_usermodehelper() to use a namespace

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Date:	Sun, 8 Feb 2015 20:00:19 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Ian Kent <ikent@...hat.com>
Cc:	Kernel Mailing List <linux-kernel@...r.kernel.org>,
	David Howells <dhowells@...hat.com>,
	Trond Myklebust <trond.myklebust@...marydata.com>,
	"J. Bruce Fields" <bfields@...ldses.org>,
	Benjamin Coddington <bcodding@...hat.com>,
	Al Viro <viro@...IV.linux.org.uk>,
	Jeff Layton <jeff.layton@...marydata.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: [RFC PATCH 3/8] kmod - teach call_usermodehelper() to use a
	namespace

On 02/05, Ian Kent wrote:
>
> +int umh_enter_ns(struct task_struct *tsk, struct cred *new)
> +{
> +	char path[NS_PATH_MAX];
> +	struct vfsmount *mnt;
> +	const char *name;
> +	pid_t pid;
> +	int err = 0;
> +
> +	pid = task_pid_nr(tsk);
> +
> +	/*
> +	 * The user mode thread runner runs in the root init namespace
> +	 * so it will see all system pids.
> +	 */
> +	mnt = task_active_pid_ns(current)->proc_mnt;
> +
> +	for (name = ns_names[0]; *name; name++) {
> +		struct file *this;
> +		int len;
> +
> +		len = snprintf(path,
> +			       NS_PATH_MAX, NS_PATH_FMT,
> +			       (unsigned long) pid, name);
> +		if (len >= NS_PATH_MAX) {
> +			err = -ENAMETOOLONG;
> +			break;
> +		}
> +
> +		this = file_open_root(mnt->mnt_root, mnt, path, O_RDONLY);
> +		if (unlikely(IS_ERR(this))) {
> +			err = PTR_ERR(this);
> +			break;
> +		}
> +
> +		err = setns_inode(file_inode(this), 0);
> +		fput(this);
> +		if (err)
> +			break;
> +	}
> +
> +	return err;
> +}

Yes, I need to actually read this series and setns paths, but at first glance
there must be a simpler method to call ops->install's and switch_task_namespaces.

Sorry if this was already discussed before, but to me it looks a bit strange
to abuse /proc/ files for this. And again, iiuc file_open_root() can fail if
tsk has already exited (init can be multithreaded).

Oleg.

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