Message-ID: <20080429231819.GA27705@sergelap.austin.ibm.com>
Date:	Tue, 29 Apr 2008 18:18:19 -0500
From:	"Serge E. Hallyn" <serue@...ibm.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Benjamin Thery <benjamin.thery@...l.net>,
	linux-kernel@...r.kernel.org, Tejun Heo <htejun@...il.com>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Daniel Lezcano <dlezcano@...ibm.com>,
	"Serge E. Hallyn" <serue@...ibm.com>,
	Pavel Emelyanov <xemul@...nvz.org>, netdev@...r.kernel.org
Subject: Re: [PATCH 10/10] sysfs: user namespaces: add ns to user_struct

Quoting Eric W. Biederman (ebiederm@...ssion.com):
> Benjamin Thery <benjamin.thery@...l.net> writes:
> 
> > Add the user_namespace to user_struct.
> >
> > Add a user_namespace to the sysfs_tag struct.
> >
> > Mark the /sys/kernel/uids directory to be tagged so that processes in
> > different user namespaces can remount /sys and see their own uid
> > listings.
> >
> > Without this patch, having CONFIG_FAIR_SCHED=y makes user namespaces
> > unusable, because when you
> >   clone(CLONE_NEWUSER)
> > it will auto-create the root userid and try to create
> > /sys/kernel/uids/0.  Since that already exists from the parent user
> > namespace, the create fails, and the clone misleadingly ends up
> > returning -ENOMEM.
> >
> > This patch fixes the issue by allowing each user namespace to remount
> > /sys, and having /sys filter the /sys/kernel/uid/ entries by user
> > namespace.
> 
> There is a lot of promising code in this patch.  This patch appears to
> be building up a lot of userns infrastructure that is only indirectly
> related to sysfs, and it still appears to have some debugging code
> present.  

Good point.

I left in more cruft than I thought I had.  Really the k_uid_t
shouldn't be there at all.  But to have any fix at all I do need the
user_namespace in the user_struct.  So unless you're ok with putting
that in explicitly for now, then until we decide how to handle the
user_struct being in multiple namespaces, the fix will have to wait.

> As a proof of concept patch (which I asked for) this looks good.
> 
> I do think this patch should get split into logical changes
> and cleaned up a bit before it gets merged into mainline.

Agreed.  I didn't pull out enough for the simple sysfs fix.

> More comments inline below.
> 
> Eric
> 
> > Index: linux-mm/fs/sysfs/mount.c
> > ===================================================================
> > --- linux-mm.orig/fs/sysfs/mount.c
> > +++ linux-mm/fs/sysfs/mount.c
> > @@ -17,6 +17,7 @@
> >  #include <linux/pagemap.h>
> >  #include <linux/init.h>
> >  #include <linux/nsproxy.h>
> > +#include <linux/user_namespace.h>
> >  #include <net/net_namespace.h>
> >  
> >  #include "sysfs.h"
> > @@ -81,6 +82,7 @@ static int sysfs_fill_super(struct super
> >  	sb->s_root = root;
> >  	sb->s_fs_info = info;
> >  	info->tag.net_ns = hold_net(current->nsproxy->net_ns);
> > +	info->tag.user_ns = current->nsproxy->user_ns;
> >  	return 0;
> >  
> >  out_err:
> > @@ -100,6 +102,8 @@ static int sysfs_test_super(struct super
> >  
> >  	if (task->nsproxy->net_ns != info->tag.net_ns)
> >  		found = 0;
> > +	if (task->nsproxy->user_ns != info->tag.user_ns)
> > +		found = 0;
> >  
> >  	return found;
> >  }
> > @@ -214,6 +218,27 @@ static struct pernet_operations sysfs_ne
> >  };
> >  #endif
> >  
> > +#ifdef CONFIG_USER_NS
> > +void sysfs_userns_exit(struct user_namespace *user_ns)
> > +{
> > +	/* Allow the net namespace to go away while sysfs is still mounted. */
> > +	struct super_block *sb;
> > +	printk(KERN_NOTICE "sysfs: user namespace exiting\n");
> Debugging?

Yes, sorry.

> > +	mutex_lock(&sysfs_rename_mutex);
> > +	sysfs_grab_supers();
> > +	mutex_lock(&sysfs_mutex);
> > +	list_for_each_entry(sb, &sysfs_fs_type.fs_supers, s_instances) {
> > +		struct sysfs_super_info *info = sysfs_info(sb);
> > +		if (info->tag.user_ns != user_ns)
> > +			continue;
> > +		info->tag.user_ns = NULL;
> > +	}
> > +	mutex_unlock(&sysfs_mutex);
> > +	sysfs_release_supers();
> > +	mutex_unlock(&sysfs_rename_mutex);
> > +}
> > +#endif
> > +
> >  int __init sysfs_init(void)
> >  {
> >  	int err = -ENOMEM;
> > Index: linux-mm/include/linux/sched.h
> > ===================================================================
> > --- linux-mm.orig/include/linux/sched.h
> > +++ linux-mm/include/linux/sched.h
> > @@ -598,7 +598,7 @@ struct user_struct {
> >  
> >  	/* Hash table maintenance information */
> >  	struct hlist_node uidhash_node;
> > -	uid_t uid;
> > +	struct k_uid_t uid;
> 
> If we are going to go this direction my inclination
> is to include an array of a single element in user_struct.
> 
> Maybe that makes sense.  I just know we need to talk about
> how a user maps into different user namespaces.  As that

My thought had been that a task belongs to several user_structs, but
each user_struct belongs to just one user namespace.  Maybe as you
suggest that's not the right way to go.

But are you ok with just sticking a user_namespace * in here for now,
and making it clear that the user_struct-user_namespace relation is yet
to be defined?

If not that's fine, we just won't be able to clone(CLONE_NEWUSER)
until we get the relationship straightened out.

> is a real concept that really occurs in real filesystems
> like nfsv4 and p9fs, and having infrastructure that can
> deal with the concept (even if it doesn't support it yet) would be
> useful.

I'll have to look at 9p, bc right now I don't know what you're talking
about.  Then I'll move to the containers list to discuss what the
user_struct should look like.

Thanks for taking a look.

-serge

> >  #endif /* _SYSFS_H_ */
> > Index: linux-mm/include/linux/types.h
> > ===================================================================
> > --- linux-mm.orig/include/linux/types.h
> > +++ linux-mm/include/linux/types.h
> > @@ -37,6 +37,11 @@ typedef __kernel_gid32_t	gid_t;
> >  typedef __kernel_uid16_t        uid16_t;
> >  typedef __kernel_gid16_t        gid16_t;
> >  
> > +struct k_uid_t {
> > +	uid_t uid;
> > +	struct user_namespace *ns;
> > +};
> 
> Weird a _t suffix in a structure name.  Usually _t indicates
> that something is a typedef.
> 
> > +
> >  typedef unsigned long		uintptr_t;
> >  
> >  #ifdef CONFIG_UID16
> > Index: linux-mm/include/linux/user_namespace.h
> > ===================================================================
> > --- linux-mm.orig/include/linux/user_namespace.h
> > +++ linux-mm/include/linux/user_namespace.h
> > @@ -12,10 +12,15 @@
> >  struct user_namespace {
> >  	struct kref		kref;
> >  	struct hlist_head	uidhash_table[UIDHASH_SZ];
> > +	struct kset		*kset;
> >  	struct user_struct	*root_user;
> >  };
> >  
> >  extern struct user_namespace init_user_ns;
> > +extern int register_user_ns_kobj(struct user_namespace *ns);
> > +extern void unregister_user_ns_kobj(struct user_namespace *ns);
> > +extern int register_user_ns_kobj(struct user_namespace *ns);
> > +extern void unregister_user_ns_kobj(struct user_namespace *ns);
> >  
> >  #ifdef CONFIG_USER_NS
> >  
> > Index: linux-mm/kernel/user.c
> > ===================================================================
> > --- linux-mm.orig/kernel/user.c
> > +++ linux-mm/kernel/user.c
> > @@ -53,6 +53,10 @@ struct user_struct root_user = {
> >  	.files		= ATOMIC_INIT(0),
> >  	.sigpending	= ATOMIC_INIT(0),
> >  	.locked_shm     = 0,
> > +	.uid		= {
> > +		.uid = 0,
> > +		.ns = &init_user_ns,
> > +	},
> >  #ifdef CONFIG_USER_SCHED
> >  	.tg		= &init_task_group,
> >  #endif
> > @@ -71,13 +75,23 @@ static void uid_hash_remove(struct user_
> >  	hlist_del_init(&up->uidhash_node);
> >  }
> >  
> > -static struct user_struct *uid_hash_find(uid_t uid, struct hlist_head *hashent)
> > +int task_user_equiv(struct task_struct *tsk, struct user_struct *u)
> > +{
> > +	if (tsk->uid != u->uid.uid)
> > +		return 0;
> > +	if (tsk->nsproxy->user_ns != u->uid.ns)
> > +		return 0;
> > +	return 1;
> > +}
> > +
> > +static struct user_struct *uid_hash_find(uid_t uid,
> > +				struct hlist_head *hashent)
> >  {
> >  	struct user_struct *user;
> >  	struct hlist_node *h;
> >  
> >  	hlist_for_each_entry(user, h, hashent, uidhash_node) {
> > -		if (user->uid == uid) {
> > +		if (user->uid.uid == uid) {
> >  			atomic_inc(&user->__count);
> >  			return user;
> >  		}
> > @@ -236,6 +250,23 @@ static void uids_release(struct kobject 
> >  	return;
> >  }
> >  
> > +static const void *userns_sb_tag(struct sysfs_tag_info *info)
> > +{
> > +       return info->user_ns;
> > +}
> > +
> > +static const void *userns_kobject_tag(struct kobject *kobj)
> > +{
> > +       struct user_struct *up;
> > +       up = container_of(kobj, struct user_struct, kobj);
> > +       return up->uid.ns;
> > +}
> > +
> > +static struct sysfs_tagged_dir_operations userns_tagged_dir_operations = {
> > +       .sb_tag = userns_sb_tag,
> > +       .kobject_tag = userns_kobject_tag,
> > +};
> > +
> >  static struct kobj_type uids_ktype = {
> >  	.sysfs_ops = &kobj_sysfs_ops,
> >  	.default_attrs = uids_attributes,
> > @@ -246,19 +277,19 @@ static struct kobj_type uids_ktype = {
> >  static int uids_user_create(struct user_struct *up)
> >  {
> >  	struct kobject *kobj = &up->kobj;
> > -	int error;
> > +	int err;
> >  
> >  	memset(kobj, 0, sizeof(struct kobject));
> >  	kobj->kset = uids_kset;
> > -	error = kobject_init_and_add(kobj, &uids_ktype, NULL, "%d", up->uid);
> > -	if (error) {
> > +	err = kobject_init_and_add(kobj, &uids_ktype, NULL, "%d", up->uid.uid);
> > +	if (err) {
> >  		kobject_put(kobj);
> >  		goto done;
> >  	}
> >  
> >  	kobject_uevent(kobj, KOBJ_ADD);
> >  done:
> > -	return error;
> > +	return err;
> >  }
> >  
> >  /* create these entries in sysfs:
> > @@ -271,7 +302,7 @@ int __init uids_sysfs_init(void)
> >  	uids_kset = kset_create_and_add("uids", NULL, kernel_kobj);
> >  	if (!uids_kset)
> >  		return -ENOMEM;
> > -
> > +	sysfs_enable_tagging(&uids_kset->kobj, &userns_tagged_dir_operations);
> >  	return uids_user_create(&root_user);
> >  }
> >  
> > @@ -403,7 +434,8 @@ struct user_struct *alloc_uid(struct use
> >  		if (!new)
> >  			goto out_unlock;
> >  
> > -		new->uid = uid;
> > +		new->uid.uid = uid;
> > +		new->uid.ns = ns;
> >  		atomic_set(&new->__count, 1);
> >  
> >  		if (sched_create_user(new) < 0)
> > Index: linux-mm/kernel/user_namespace.c
> > ===================================================================
> > --- linux-mm.orig/kernel/user_namespace.c
> > +++ linux-mm/kernel/user_namespace.c
> > @@ -22,7 +22,7 @@ static struct user_namespace *clone_user
> >  	struct user_struct *new_user;
> >  	int n;
> >  
> > -	ns = kmalloc(sizeof(struct user_namespace), GFP_KERNEL);
> > +	ns = kzalloc(sizeof(struct user_namespace), GFP_KERNEL);
> >  	if (!ns)
> >  		return ERR_PTR(-ENOMEM);
> >  
> > @@ -71,6 +71,7 @@ void free_user_ns(struct kref *kref)
> >  	struct user_namespace *ns;
> >  
> >  	ns = container_of(kref, struct user_namespace, kref);
> > +	sysfs_userns_exit(ns);
> >  	release_uids(ns);
> >  	kfree(ns);
> >  }
--
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