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Message-ID: <CAGXu5jK0vt9WAaX4a5ihV+iVGFSnn0JJOKAVXocg2VqMV+rxBg@mail.gmail.com>
Date: Tue, 16 Aug 2016 13:00:21 -0700
From: Kees Cook <keescook@...omium.org>
To: Andrei Vagin <avagin@...nvz.org>
Cc: "Eric W. Biederman" <ebiederm@...ssion.com>,
Linux Containers <containers@...ts.linux-foundation.org>,
LKML <linux-kernel@...r.kernel.org>,
Serge Hallyn <serge.hallyn@...onical.com>
Subject: Re: [PATCH 1/2] kernel: show current values of user namespace counters
On Mon, Aug 15, 2016 at 1:10 PM, Andrei Vagin <avagin@...nvz.org> 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@...onical.com>
> Cc: Kees Cook <keescook@...omium.org>
> Cc: "Eric W. Biederman" <ebiederm@...ssion.com>
> Signed-off-by: Andrei Vagin <avagin@...nvz.org>
> ---
> 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
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