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    Subject[PATCH 11/11] sysfs: user namespaces: fix bug with clone(CLONE_NEWUSER) with fairsched
    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 ++
    kernel/user.c | 21 +++++++++++++++++++++
    kernel/user_namespace.c | 13 ++++++++++++-
    5 files changed, 39 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
    @@ -604,6 +604,7 @@ 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;

    extern int kobject_set_name(struct kobject *kobj, const char *name, ...)
    __attribute__((format(printf, 2, 3)));
    @@ -83,6 +84,7 @@ struct sysfs_ops {

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

    struct sysfs_tagged_dir_operations {
    Index: linux-mm/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);
    }
    --


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