[PATCH 11/11] sysfs: user namespaces: fix bug with clone(CLONE_NEWUSER) with fairsched

Benjamin Thery
2008-06-06T15:51:30Z

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.

Signed-off-by: Serge Hallyn <serue@us.ibm.com>
Signed-off-by: Benjamin Thery <benjamin.thery@bull.net>
---
fs/sysfs/mount.c | 3 +++
include/linux/sched.h | 1 +
include/linux/sysfs.h | 2 ++
include/linux/user_namespace.h | 1 +
kernel/user.c | 21 +++++++++++++++++++++
kernel/user_namespace.c | 13 ++++++++++++-
6 files changed, 40 insertions(+), 1 deletion(-)

Index: linux-mm/fs/sysfs/mount.c
===================================================================
--- linux-mm.orig/fs/sysfs/mount.c
+++ linux-mm/fs/sysfs/mount.c
@@ -81,6 +81,7 @@ 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 +101,8 @@ 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;
}
Index: linux-mm/include/linux/sched.h
===================================================================
--- linux-mm.orig/include/linux/sched.h
+++ linux-mm/include/linux/sched.h
@@ -600,6 +600,7 @@ struct user_struct {
/* Hash table maintenance information */
struct hlist_node uidhash_node;
uid_t uid;
+ struct user_namespace *user_ns;

#ifdef CONFIG_USER_SCHED
struct task_group *tg;
Index: linux-mm/include/linux/sysfs.h
===================================================================
--- linux-mm.orig/include/linux/sysfs.h
+++ linux-mm/include/linux/sysfs.h
@@ -20,6 +20,7 @@
struct kobject;
struct module;
struct net;
+struct user_namespace;

/* FIXME
* The *owner field is no longer used, but leave around
@@ -81,6 +82,7 @@ struct sysfs_ops {

struct sysfs_tag_info {
struct net *net_ns;
+ struct user_namespace *user_ns;
};

struct sysfs_tagged_dir_operations {
Index: linux-mm/include/linux/user_namespace.h
===================================================================
--- linux-mm.orig/include/linux/user_namespace.h
+++ linux-mm/include/linux/user_namespace.h
@@ -12,6 +12,7 @@
struct user_namespace {
struct kref kref;
struct hlist_head uidhash_table[UIDHASH_SZ];
+ struct kset *kset;
struct user_struct *root_user;
};

Index: linux-mm/kernel/user.c
===================================================================
--- linux-mm.orig/kernel/user.c
+++ linux-mm/kernel/user.c
@@ -53,6 +53,7 @@ struct user_struct root_user = {
.files = ATOMIC_INIT(0),
.sigpending = ATOMIC_INIT(0),
.locked_shm = 0,
+ .user_ns = &init_user_ns,
#ifdef CONFIG_USER_SCHED
.tg = &init_task_group,
#endif
@@ -236,6 +237,23 @@ 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->user_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,
@@ -272,6 +290,8 @@ int __init uids_sysfs_init(void)
if (!uids_kset)
return -ENOMEM;

+ sysfs_enable_tagging(&uids_kset->kobj, &userns_tagged_dir_operations);
+
return uids_user_create(&root_user);
}

@@ -404,6 +424,7 @@ struct user_struct *alloc_uid(struct use
goto out_unlock;

new->uid = uid;
+ new->user_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);

@@ -66,11 +66,22 @@ struct user_namespace * copy_user_ns(int
return new_ns;
}

+/* clear sysfs tag when user namespace exits */
+static void sysfs_userns_exit(struct sysfs_tag_info *tag_info, void *data)
+{
+ struct user_namespace *ns = (struct user_namespace *)data;
+
+ if (tag_info->user_ns != ns)
+ return;
+ tag_info->user_ns = NULL;
+}
+
void free_user_ns(struct kref *kref)
{
struct user_namespace *ns;

ns = container_of(kref, struct user_namespace, kref);
+ sysfs_ns_exit(sysfs_userns_exit, ns);
release_uids(ns);
kfree(ns);
}

--