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

[ebiederm@xmission.com (Eric W. Biederman)]

Ian Kent <raven@themaw.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@redhat.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.

Eric