linux-kernel - Re: [RFC PATCH v4 03/12] vfs - move mnt_namespace definition to linux/mount.h

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Message-ID: <1426813025.2724.2.camel@pluto.fritz.box>
Date:	Fri, 20 Mar 2015 08:57:05 +0800
From:	Ian Kent <raven@...maw.net>
To:	Al Viro <viro@...IV.linux.org.uk>
Cc:	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>,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: [RFC PATCH v4 03/12] vfs - move mnt_namespace definition to
 linux/mount.h

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.

Ian

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