Re: [PATCH 03/11] pidns: Capture the user namespace and filter ns_last_pid

[Zhao Hongjiang <zhaohongjiang37-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

On 2012/11/17 0:35, Eric W. Biederman wrote:
> From: "Eric W. Biederman" <ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org>
>
> - Capture the the user namespace that creates the pid namespace
> - Use that user namespace to test if it is ok to write to
>   /proc/sys/kernel/ns_last_pid.
>
> Acked-by: Serge Hallyn <serge.hallyn-Z7WLFzj8eWMS+FvcfC7Uqw@public.gmane.org>
> Signed-off-by: "Eric W. Biederman" <ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org>
> ---
>  include/linux/pid_namespace.h |    8 +++++---
>  kernel/nsproxy.c              |    2 +-
>  kernel/pid.c                  |    1 +
>  kernel/pid_namespace.c        |   16 +++++++++++-----
>  4 files changed, 18 insertions(+), 9 deletions(-)
>
> diff --git a/include/linux/pid_namespace.h b/include/linux/pid_namespace.h
> index 65e3e87..c89c9cf 100644
> --- a/include/linux/pid_namespace.h
> +++ b/include/linux/pid_namespace.h
> @@ -31,6 +31,7 @@ struct pid_namespace {
>  #ifdef CONFIG_BSD_PROCESS_ACCT
>  	struct bsd_acct_struct *bacct;
>  #endif
> +	struct user_namespace *user_ns;
>  	kgid_t pid_gid;
>  	int hide_pid;
>  	int reboot;	/* group exit code if this pidns was rebooted */
> @@ -46,7 +47,8 @@ static inline struct pid_namespace *get_pid_ns(struct pid_namespace *ns)
>  	return ns;
>  }
>
> -extern struct pid_namespace *copy_pid_ns(unsigned long flags, struct pid_namespace *ns);
> +extern struct pid_namespace *copy_pid_ns(unsigned long flags,
> +	struct user_namespace *user_ns, struct pid_namespace *ns);
>  extern void zap_pid_ns_processes(struct pid_namespace *pid_ns);
>  extern int reboot_pid_ns(struct pid_namespace *pid_ns, int cmd);
>  extern void put_pid_ns(struct pid_namespace *ns);
> @@ -59,8 +61,8 @@ static inline struct pid_namespace *get_pid_ns(struct pid_namespace *ns)
>  	return ns;
>  }
>
> -static inline struct pid_namespace *
> -copy_pid_ns(unsigned long flags, struct pid_namespace *ns)
> +static inline struct pid_namespace *copy_pid_ns(unsigned long flags,
> +	struct user_namespace *user_ns, struct pid_namespace *ns)
>  {
>  	if (flags & CLONE_NEWPID)
>  		ns = ERR_PTR(-EINVAL);
> diff --git a/kernel/nsproxy.c b/kernel/nsproxy.c
> index b576f7f..5fe88e1 100644
> --- a/kernel/nsproxy.c
> +++ b/kernel/nsproxy.c
> @@ -84,7 +84,7 @@ static struct nsproxy *create_new_namespaces(unsigned long flags,
>  		goto out_ipc;
>  	}
>
> -	new_nsp->pid_ns = copy_pid_ns(flags, task_active_pid_ns(tsk));
> +	new_nsp->pid_ns = copy_pid_ns(flags, task_cred_xxx(tsk, user_ns), task_active_pid_ns(tsk));
>  	if (IS_ERR(new_nsp->pid_ns)) {
>  		err = PTR_ERR(new_nsp->pid_ns);
>  		goto out_pid;
> diff --git a/kernel/pid.c b/kernel/pid.c
> index aebd4f5..2a624f1 100644
> --- a/kernel/pid.c
> +++ b/kernel/pid.c
> @@ -78,6 +78,7 @@ struct pid_namespace init_pid_ns = {
>  	.last_pid = 0,
>  	.level = 0,
>  	.child_reaper = &init_task,
> +	.user_ns = &init_user_ns,
>  };
>  EXPORT_SYMBOL_GPL(init_pid_ns);
>
> diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c
> index 7b07cc0..7580aa0 100644
> --- a/kernel/pid_namespace.c
> +++ b/kernel/pid_namespace.c
> @@ -10,6 +10,7 @@
>
>  #include <linux/pid.h>
>  #include <linux/pid_namespace.h>
> +#include <linux/user_namespace.h>
>  #include <linux/syscalls.h>
>  #include <linux/err.h>
>  #include <linux/acct.h>
> @@ -74,7 +75,8 @@ err_alloc:
>  /* MAX_PID_NS_LEVEL is needed for limiting size of 'struct pid' */
>  #define MAX_PID_NS_LEVEL 32
>
> -static struct pid_namespace *create_pid_namespace(struct pid_namespace *parent_pid_ns)
> +static struct pid_namespace *create_pid_namespace(struct user_namespace *user_ns,
> +	struct pid_namespace *parent_pid_ns)
>  {
>  	struct pid_namespace *ns;
>  	unsigned int level = parent_pid_ns->level + 1;
> @@ -102,6 +104,7 @@ static struct pid_namespace *create_pid_namespace(struct pid_namespace *parent_p
>  	kref_init(&ns->kref);
>  	ns->level = level;
>  	ns->parent = get_pid_ns(parent_pid_ns);
> +	ns->user_ns = get_user_ns(user_ns);

Hi Eric,

I noticed that, the increment refcount of user_ns has never released when the pid_ns's refcount is
down to zero. And i have sent out a patch to solve this on Nov 2th.

Am i misunderstand something?

Hongjiang

>
>  	set_bit(0, ns->pidmap[0].page);
>  	atomic_set(&ns->pidmap[0].nr_free, BITS_PER_PAGE - 1);
> @@ -117,6 +120,7 @@ static struct pid_namespace *create_pid_namespace(struct pid_namespace *parent_p
>
>  out_put_parent_pid_ns:
>  	put_pid_ns(parent_pid_ns);
> +	put_user_ns(user_ns);
>  out_free_map:
>  	kfree(ns->pidmap[0].page);
>  out_free:
> @@ -134,13 +138,14 @@ static void destroy_pid_namespace(struct pid_namespace *ns)
>  	kmem_cache_free(pid_ns_cachep, ns);
>  }
>
> -struct pid_namespace *copy_pid_ns(unsigned long flags, struct pid_namespace *old_ns)
> +struct pid_namespace *copy_pid_ns(unsigned long flags,
> +	struct user_namespace *user_ns, struct pid_namespace *old_ns)
>  {
>  	if (!(flags & CLONE_NEWPID))
>  		return get_pid_ns(old_ns);
>  	if (flags & (CLONE_THREAD|CLONE_PARENT))
>  		return ERR_PTR(-EINVAL);
> -	return create_pid_namespace(old_ns);
> +	return create_pid_namespace(user_ns, old_ns);
>  }
>
>  static void free_pid_ns(struct kref *kref)
> @@ -239,9 +244,10 @@ void zap_pid_ns_processes(struct pid_namespace *pid_ns)
>  static int pid_ns_ctl_handler(struct ctl_table *table, int write,
>  		void __user *buffer, size_t *lenp, loff_t *ppos)
>  {
> +	struct pid_namespace *pid_ns = task_active_pid_ns(current);
>  	struct ctl_table tmp = *table;
>
> -	if (write && !capable(CAP_SYS_ADMIN))
> +	if (write && !ns_capable(pid_ns->user_ns, CAP_SYS_ADMIN))
>  		return -EPERM;
>
>  	/*
> @@ -250,7 +256,7 @@ static int pid_ns_ctl_handler(struct ctl_table *table, int write,
>  	 * it should synchronize its usage with external means.
>  	 */
>
> -	tmp.data = &current->nsproxy->pid_ns->last_pid;
> +	tmp.data = &pid_ns->last_pid;
>  	return proc_dointvec_minmax(&tmp, write, buffer, lenp, ppos);
>  }
>
>



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