linux-kernel - Re: [PATCH 7/8] cgroup: mount cgroupns-root when inside non-init cgroupns

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20151127051745.GA24521@mail.hallyn.com>
Date:	Thu, 26 Nov 2015 23:17:45 -0600
From:	"Serge E. Hallyn" <serge.hallyn@...ntu.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	serge@...lyn.com, linux-kernel@...r.kernel.org,
	adityakali@...gle.com, linux-api@...r.kernel.org,
	containers@...ts.linux-foundation.org, cgroups@...r.kernel.org,
	lxc-devel@...ts.linuxcontainers.org, akpm@...ux-foundation.org,
	ebiederm@...ssion.com
Subject: Re: [PATCH 7/8] cgroup: mount cgroupns-root when inside non-init
 cgroupns

On Tue, Nov 24, 2015 at 12:16:10PM -0500, Tejun Heo wrote:
> Hello,
> 
> On Mon, Nov 16, 2015 at 01:51:44PM -0600, serge@...lyn.com wrote:
> > +struct dentry *kernfs_obtain_root(struct super_block *sb,
> > +				  struct kernfs_node *kn)
> > +{
> > +	struct dentry *dentry;
> > +	struct inode *inode;
> > +
> > +	BUG_ON(sb->s_op != &kernfs_sops);
> > +
> > +	/* inode for the given kernfs_node should already exist. */
> > +	inode = ilookup(sb, kn->ino);
> > +	if (!inode) {
> > +		pr_debug("kernfs: could not get inode for '");
> > +		pr_cont_kernfs_path(kn);
> > +		pr_cont("'.\n");
> > +		return ERR_PTR(-EINVAL);
> > +	}
> 
> Hmmm... but inode might not have been instantiated yet.  Why not use
> kernfs_get_inode()?
> 
> > +	/* instantiate and link root dentry */
> > +	dentry = d_obtain_root(inode);
> > +	if (!dentry) {
> > +		pr_debug("kernfs: could not get dentry for '");
> > +		pr_cont_kernfs_path(kn);
> > +		pr_cont("'.\n");
> > +		return ERR_PTR(-ENOMEM);
> > +	}
> > +
> > +	/* If this is a new dentry, set it up. We need kernfs_mutex because this
> > +	 * may be called by callers other than kernfs_fill_super. */
> 
> Formatting.
> 
> > +	mutex_lock(&kernfs_mutex);
> > +	if (!dentry->d_fsdata) {
> > +		kernfs_get(kn);
> > +		dentry->d_fsdata = kn;
> > +	} else {
> > +		WARN_ON(dentry->d_fsdata != kn);
> > +	}
> > +	mutex_unlock(&kernfs_mutex);
> > +
> > +	return dentry;
> > +}
> 
> Wouldn't it be simpler to walk dentry from kernfs root than
> duplicating dentry instantiation?

Sorry I don't think I'm following.  Are you suggesting walking the
kn->parent chain backward and doing d_lookup() at each point starting
with sb->s_root?
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/