Date:	Fri, 20 Mar 2015 10:11:45 +0800
From:	Ian Kent <raven@...maw.net>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Al Viro <viro@...IV.linux.org.uk>,
	Kernel Mailing List <linux-kernel@...r.kernel.org>,
	David Howells <dhowells@...hat.com>,
	Oleg Nesterov <onestero@...hat.com>,
	Trond Myklebust <trond.myklebust@...marydata.com>,
	"J. Bruce Fields" <bfields@...ldses.org>,
	Benjamin Coddington <bcodding@...hat.com>,
	Jeff Layton <jeff.layton@...marydata.com>
Subject: Re: [RFC PATCH v4 03/12] vfs - move mnt_namespace definition to
 linux/mount.h

On Thu, 2015-03-19 at 20:14 -0500, Eric W. Biederman wrote:
> Ian Kent <raven@...maw.net> writes:
> 
> 2> On Thu, 2015-03-19 at 19:47 +0000, Al Viro wrote:
> >> On Tue, Mar 17, 2015 at 10:45:09AM +0800, Ian Kent wrote:
> >> > From: Ian Kent <ikent@...hat.com>
> >> > 
> >> > The mnt_namespace definition will be needed by the usermode helper
> >> > contained execution implementation, move it to include/linux/mount.h.
> >> 
> >> I really don't like that.  AFAICS, the root of the evil is that fscking
> >> nsproxy keeps a pointer to mnt_namespace while all it really needs to
> >> know about is the address of ns_common field embedded into it.  Let's see...
> >
> > Thought that might be the case.
> >
> >> 
> >> fs/namespace.c:697:     struct mnt_namespace *ns = current->nsproxy->mnt_ns;
> >> fs/namespace.c:770:     return mnt->mnt_ns == current->nsproxy->mnt_ns;
> >> fs/namespace.c:1502:    return ns_capable(current->nsproxy->mnt_ns->user_ns, CAP_SYS_ADMIN);
> >> fs/namespace.c:1587:    return current->nsproxy->mnt_ns->seq >= mnt_ns->seq;
> >> fs/namespace.c:2293:    struct user_namespace *user_ns = current->nsproxy->mnt_ns->user_ns;
> >> fs/namespace.c:2961:    touch_mnt_namespace(current->nsproxy->mnt_ns);
> >> fs/namespace.c:3003:    init_task.nsproxy->mnt_ns = ns;
> >> fs/namespace.c:3101:    ns_root.mnt = &current->nsproxy->mnt_ns->root->mnt;
> >> fs/namespace.c:3119:    struct mnt_namespace *ns = current->nsproxy->mnt_ns;
> >> fs/namespace.c:3159:            ns = &nsproxy->mnt_ns->ns;
> >> fs/namespace.c:3187:    put_mnt_ns(nsproxy->mnt_ns);
> >> fs/namespace.c:3188:    nsproxy->mnt_ns = mnt_ns;
> >> fs/pnode.c:282: user_ns = current->nsproxy->mnt_ns->user_ns;
> >> fs/proc_namespace.c:246:        if (!nsp || !nsp->mnt_ns) {
> >> fs/proc_namespace.c:251:        ns = nsp->mnt_ns;
> >> include/linux/nsproxy.h:33:     struct mnt_namespace *mnt_ns;
> >> kernel/nsproxy.c:37:    .mnt_ns                 = NULL,
> >> kernel/nsproxy.c:70:    new_nsp->mnt_ns = copy_mnt_ns(flags, tsk->nsproxy->mnt_ns, user_ns, new_fs);
> >> kernel/nsproxy.c:71:    if (IS_ERR(new_nsp->mnt_ns)) {
> >> kernel/nsproxy.c:72:            err = PTR_ERR(new_nsp->mnt_ns);
> >> kernel/nsproxy.c:113:   if (new_nsp->mnt_ns)
> >> kernel/nsproxy.c:114:           put_mnt_ns(new_nsp->mnt_ns);
> >> kernel/nsproxy.c:160:   if (ns->mnt_ns)
> >> kernel/nsproxy.c:161:           put_mnt_ns(ns->mnt_ns);
> >> 
> >> OK, so we need
> >> 
> >> a) add in fs/mount.h
> >> static inline struct mnt_namespace *current_mnt_ns(void)
> >> {
> >> 	return current->nsproxy->mnt_ns;
> >> }
> >> 
> >> and replace a lot of open-coded instances.
> >> 
> >> b) lift to_mnt_ns() into fs/mount.h (as static inline)
> >> 
> >> c) switch put_mnt_ns() to struct ns_common *, replacing put_mnt_ns(ns)
> >> with put_mnt_ns(&ns->ns) and using to_mnt_ns() in the body to recover
> >> the original.
> >> 
> >> d) make copy_mnt_ns() take and return struct ns_common * (same treatment as for
> >> put_mnt_ns() in (c); replace
> >>         new_nsp->mnt_ns = copy_mnt_ns(flags, tsk->nsproxy->mnt_ns, user_ns, new_fs);
> >>         if (IS_ERR(new_nsp->mnt_ns)) {
> >>                 err = PTR_ERR(new_nsp->mnt_ns);
> >>                 goto out_ns;
> >>         }
> >> with
> >> 	ns = copy_mnt_ns(flags, &tsk->nsproxy->mnt_ns->ns, user_ns, new_fs);
> >> 	if (IS_ERR(ns)) {
> >> 		err = PTR_ERR(ns);
> >> 		goto out_ns;
> >> 	}
> >> 	new_nsp->mnt_ns = to_mnt_ns(ns);
> >> 
> >> e) replace struct mnt_namespace *mnt_ns with struct ns_common *__mnt_ns in
> >> nsproxy.h, deal with users of mnt_ns by
> >> * everywhere in the tree replace put_mnt_ns(&...->mnt_ns->ns) with
> >> put_mnt_ns(...->__mnt_ns) (i.e. modify the lines modified by (c) again).
> >> * in fs/namespace.c replace
> >> 	init_task.nsproxy->mnt_ns = ns;
> >> with
> >> 	init_task.nsproxy->__mnt_ns = &ns->ns;
> >> replace
> >> 	ns = &nsproxy->mnt_ns->ns;
> >> with
> >> 	ns = nsproxy->__mnt_ns;
> >> replace
> >> 	nsproxy->mnt_ns = mnt_ns;
> >> with
> >> 	nsproxy>__mnt_ns = &mnt_ns->ns;
> >> * in fs/proc_namespace.c replace
> >> 	ns = nsp->mnt_ns;
> >> with
> >> 	ns = to_mnt_ns(nsp->__mnt_ns);
> >> and
> >> 	if (!nsp || !nsp->mnt_ns) {
> >> with
> >> 	if (!nsp || !nsp->__mnt_ns) {
> >> * in kernel/nsproxy.c: replace
> >> 	ns = copy_mnt_ns(flags, &tsk->nsproxy->mnt_ns->ns, user_ns, new_fs);
> >> added in (d) with
> >> 	ns = copy_mnt_ns(flags, tsk->nsproxy->__mnt_ns, user_ns, new_fs);
> >> and
> >> 	new_nsp->mnt_ns = to_mnt_ns(ns);
> >> with
> >> 	new_nsp->__mnt_ns = ns;
> >> The rest of mnt_ns in that file get replaced by __mnt_ns.
> >> * in current_mnt_ns() replace ...->mnt_ns with to_mnt_ns(...->__mnt_ns)
> >> 
> >> Do you want me to push such a series in vfs.git?  After such 5 commits we have
> >> no pointers to struct mnt_namespace in nsproxy.h *and* no need for your patches
> >> to dig into ->mnt_ns->ns - we already have that as ->__mnt_ns.
> >
> > Yes please, I'd be more confident if you did this than me, there's
> > already enough to worry about with the series.
> 
> Given that this patchset is a security hole waiting to happen I don't
> see why Al should bother unless there are good reasons to do this
> otherwise.

Having now got to your mail now, I agree.

> 
> Eric


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