Re: [PATCH 1/2] kernel: show current values of user namespace counters

[Kees Cook]

On Mon, Aug 15, 2016 at 1:10 PM, Andrei Vagin <avagin@xxxxxxxxxx> wrote:
> Recently Eric added user namespace counters.  User namespace counters is
> a feature that allows to limit the number of various kernel objects a
> user can create. These limits are set via /proc/sys/user/ sysctls on a
> per user namespace basis and are applicable to all users in that
> namespace.
>
> This patch adds /proc/PID/userns_counts files to provide current usage
> of user namespace counters.
>
>   > cat /proc/813/userns_counts
>   user_namespaces          101000               1
>   pid_namespaces           101000               1
>   ipc_namespaces           101000               4
>   net_namespaces           101000               2
>   mnt_namespaces           101000               5
>   mnt_namespaces           100000               1
>
> The meanings of the columns are as follows, from left to right:
>
>   Name         Object name
>   UID          User ID
>   Usage        Current usage
>
> Cc: Serge Hallyn <serge.hallyn@xxxxxxxxxxxxx>
> Cc: Kees Cook <keescook@xxxxxxxxxxxx>
> Cc: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
> Signed-off-by: Andrei Vagin <avagin@xxxxxxxxxx>
> ---
>  fs/proc/array.c                |  57 +++++++++++++++++++++++
>  fs/proc/base.c                 |   3 ++
>  fs/proc/internal.h             |   1 +
>  include/linux/user_namespace.h |   8 ++++
>  kernel/ucount.c                | 102 +++++++++++++++++++++++++++++++++++++++++
>  5 files changed, 171 insertions(+)
>
> diff --git a/fs/proc/array.c b/fs/proc/array.c
> index 88c7de1..f186625 100644
> --- a/fs/proc/array.c
> +++ b/fs/proc/array.c
> @@ -734,3 +734,60 @@ const struct file_operations proc_tid_children_operations = {
>         .release = children_seq_release,
>  };
>  #endif /* CONFIG_PROC_CHILDREN */
> +
> +#ifdef CONFIG_USER_NS
> +static int ucounts_open(struct inode *inode, struct file *filp)
> +{
> +       struct ucounts_iterator *iter;
> +       struct seq_file *seq;
> +       int ret;
> +
> +       struct task_struct *task;
> +       struct user_namespace *ns;
> +
> +       task = get_proc_task(inode);
> +       if (!task)
> +               return -ESRCH;
> +
> +       rcu_read_lock();
> +       ns = get_user_ns(__task_cred(task)->user_ns);
> +       rcu_read_unlock();
> +
> +       put_task_struct(task);
> +
> +       if (ns == NULL)
> +               return -ESRCH;
> +
> +       ret = seq_open_private(filp, &ucounts_seq_operations,
> +                                       sizeof(struct ucounts_iterator));
> +
> +       if (ret) {
> +               put_user_ns(ns);
> +               return ret;
> +       }
> +
> +       seq = filp->private_data;
> +       iter = seq->private;
> +       iter->ns = ns;
> +
> +       return 0;
> +}
> +
> +int ucounts_release(struct inode *inode, struct file *file)
> +{
> +       struct seq_file *seq = file->private_data;
> +       struct ucounts_iterator *iter = seq->private;
> +
> +       put_user_ns(iter->ns);
> +
> +       return seq_release_private(inode, file);
> +}
> +
> +
> +const struct file_operations proc_ucounts_operations = {
> +       .open           = ucounts_open,
> +       .read           = seq_read,
> +       .llseek         = seq_lseek,
> +       .release        = ucounts_release,
> +};
> +#endif /* CONFIG_USER_NS */
> diff --git a/fs/proc/base.c b/fs/proc/base.c
> index 54e2702..4252f7a 100644
> --- a/fs/proc/base.c
> +++ b/fs/proc/base.c
> @@ -2910,6 +2910,9 @@ static const struct pid_entry tgid_base_stuff[] = {
>         REG("timers",     S_IRUGO, proc_timers_operations),
>  #endif
>         REG("timerslack_ns", S_IRUGO|S_IWUGO, proc_pid_set_timerslack_ns_operations),
> +#ifdef CONFIG_USER_NS
> +       REG("userns_counts",  S_IRUGO, proc_ucounts_operations),
> +#endif
>  };
>
>  static int proc_tgid_base_readdir(struct file *file, struct dir_context *ctx)
> diff --git a/fs/proc/internal.h b/fs/proc/internal.h
> index 7931c55..845cadb 100644
> --- a/fs/proc/internal.h
> +++ b/fs/proc/internal.h
> @@ -298,6 +298,7 @@ extern const struct file_operations proc_pid_smaps_operations;
>  extern const struct file_operations proc_tid_smaps_operations;
>  extern const struct file_operations proc_clear_refs_operations;
>  extern const struct file_operations proc_pagemap_operations;
> +extern const struct file_operations proc_ucounts_operations;
>
>  extern unsigned long task_vsize(struct mm_struct *);
>  extern unsigned long task_statm(struct mm_struct *,
> diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
> index 30ffe10..5f824dd 100644
> --- a/include/linux/user_namespace.h
> +++ b/include/linux/user_namespace.h
> @@ -106,6 +106,14 @@ extern ssize_t proc_setgroups_write(struct file *, const char __user *, size_t,
>  extern int proc_setgroups_show(struct seq_file *m, void *v);
>  extern bool userns_may_setgroups(const struct user_namespace *ns);
>  extern bool current_in_userns(const struct user_namespace *target_ns);
> +
> +struct ucounts_iterator {
> +       struct user_namespace *ns;
> +       int     hash;
> +};
> +
> +extern const struct seq_operations ucounts_seq_operations;
> +
>  #else
>
>  static inline struct user_namespace *get_user_ns(struct user_namespace *ns)
> diff --git a/kernel/ucount.c b/kernel/ucount.c
> index 6ebbe9b..cef09e3 100644
> --- a/kernel/ucount.c
> +++ b/kernel/ucount.c
> @@ -9,6 +9,8 @@
>  #include <linux/sysctl.h>
>  #include <linux/slab.h>
>  #include <linux/hash.h>
> +#include <linux/seq_file.h>
> +#include <linux/proc_fs.h>
>  #include <linux/user_namespace.h>
>
>  #define UCOUNTS_HASHTABLE_BITS 10
> @@ -232,4 +234,104 @@ static __init int user_namespace_sysctl_init(void)
>  }
>  subsys_initcall(user_namespace_sysctl_init);
>
> +#ifdef CONFIG_PROC_FS
> +static void *ucounts_start(struct seq_file *f, loff_t *pos)
> +{
> +       struct ucounts_iterator *iter = f->private;
> +       int h, i = 0;
> +
> +       spin_lock(&ucounts_lock);

This series is much improved, thanks! However, I still don't think
it's a good idea to hold this spinlock across the start/stop lifetime.
It creates too many opportunities for abuse. :( Perhaps Eric will have
some better ideas about how to deal with this...

-Kees

> +       for (h = 0; h < (1 << UCOUNTS_HASHTABLE_BITS); h++) {
> +               struct ucounts *ucounts;
> +
> +               hlist_for_each_entry(ucounts, &ucounts_hashtable[h], node) {
> +                       if (ucounts->ns != iter->ns)
> +                               continue;
> +                       if (i++ < *pos)
> +                               continue;
> +
> +                       iter->hash = h;
> +
> +                       return ucounts;
> +               }
> +       }
> +
> +       return NULL;
> +}
> +
> +static void ucounts_stop(struct seq_file *f, void *v)
> +{
> +       spin_unlock(&ucounts_lock);
> +}
> +
> +static void *ucounts_next(struct seq_file *f, void *v, loff_t *pos)
> +{
> +       struct ucounts_iterator *iter = f->private;
> +       struct ucounts *ucounts = v;
> +       int h;
> +
> +       ++*pos;
> +
> +       for (h = iter->hash; h < (1 << UCOUNTS_HASHTABLE_BITS); h++) {
> +               struct hlist_node *node;
> +
> +               if (ucounts == NULL) {
> +                       node = ucounts_hashtable[h].first;
> +                       iter->hash = h;
> +               } else
> +                       node = ucounts->node.next;
> +
> +               ucounts = hlist_entry(node, struct ucounts, node);
> +
> +               hlist_for_each_entry_from(ucounts, node) {
> +                       if (ucounts->ns != iter->ns)
> +                               continue;
> +
> +                       return ucounts;
> +               }
> +
> +               ucounts = NULL;
> +       }
> +
> +       return NULL;
> +}
> +
> +static int ucounts_show(struct seq_file *f, void *v)
> +{
> +       static const char * const ns_strs[] = {
> +                               "user_namespaces",
> +                               "pid_namespaces",
> +                               "uts_namespaces",
> +                               "ipc_namespaces",
> +                               "net_namespaces",
> +                               "mnt_namespaces",
> +                               "cgroup_namespaces",
> +                               NULL
> +       };
> +       struct user_namespace *ns = current_user_ns();
> +       struct ucounts *ucounts = v;
> +       uid_t uid;
> +       int i;
> +
> +       uid = from_kuid_munged(ns, ucounts->uid);
> +
> +       for (i = 0; ns_strs[i]; i++) {
> +               int val = atomic_read(&ucounts->ucount[i]);
> +
> +               if (val == 0)
> +                       continue;
> +
> +               seq_printf(f, "%-20s %10u\t%10d\n", ns_strs[i], uid, val);
> +       }
> +
> +       return 0;
> +}
> +
> +const struct seq_operations ucounts_seq_operations = {
> +       .start  = ucounts_start,
> +       .next   = ucounts_next,
> +       .stop   = ucounts_stop,
> +       .show   = ucounts_show,
> +};
>
> +#endif /* CONFIG_PROC_FS */
> --
> 2.5.5
>



-- 
Kees Cook
Nexus Security