Re: [PATCH] Masquerade sender information

[Pavel Emelyanov <xemul-GEFAQzZX7r8dnm+yROfE0A@public.gmane.org>]

sukadev-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org wrote:
> From: Sukadev Bhattiprolu <sukadev-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>
> Subject: [PATCH] Masquerade sender information
> 
> With multiple pid namespaces, sender of a signal could be in an ancestor
> namespace of the receiver and so the sender will not have a valid 'pid_t'
> in the receiver's namespace.
> 
> In this case, masquerade the 'siginfo' for the signal to pretend that the
> signal originated from the kernel.
> 
> Signed-off-by: Sukadev Bhattiprolu <sukadev-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>

Hmm... Definitely looks good. I thought that the problem was that 
the siginfo structure is not always allocated, but hey!, if we
failed to allocate it, then it doesn't really matter whether we 
masquerade something or not! Good point!

> ---
>  include/linux/pid.h           |    8 ++++++++
>  include/linux/pid_namespace.h |    1 +
>  kernel/pid.c                  |   13 +++++++++++++
>  kernel/signal.c               |   15 +++++++++++++++
>  4 files changed, 37 insertions(+)
> 
> Index: 2.6.23-mm1/include/linux/pid.h
> ===================================================================
> --- 2.6.23-mm1.orig/include/linux/pid.h	2007-10-27 08:48:56.000000000 -0700
> +++ 2.6.23-mm1/include/linux/pid.h	2007-10-27 09:56:53.000000000 -0700
> @@ -123,6 +123,14 @@ extern struct pid *alloc_pid(struct pid_
>  extern void FASTCALL(free_pid(struct pid *pid));
>  extern void zap_pid_ns_processes(struct pid_namespace *pid_ns);
>  
> +static inline struct pid_namespace *pid_active_ns(struct pid *pid)
> +{
> +       if (!pid)
> +               return NULL;
> +
> +       return pid->numbers[pid->level].ns;
> +}
> +
>  /*
>   * the helpers to get the pid's id seen from different namespaces
>   *
> Index: 2.6.23-mm1/kernel/pid.c
> ===================================================================
> --- 2.6.23-mm1.orig/kernel/pid.c	2007-10-27 08:50:51.000000000 -0700
> +++ 2.6.23-mm1/kernel/pid.c	2007-10-27 10:03:28.000000000 -0700
> @@ -430,6 +430,19 @@ struct pid *find_get_pid(pid_t nr)
>  	return pid;
>  }
>  
> +/*
> + * Return TRUE if the active pid namespace of @tsk is same as active
> + * pid namespace of 'current'.
> + *
> + * Note the difference between this and the task_in_pid_ns() below.
> + * task_in_pid_ns() includes processes in descendant pid name spaces
> + * but pid_ns_equal() only matches _active_ pid namespaces.
> + */
> +int pid_ns_equal(struct task_struct *tsk)
> +{
> +	return pid_active_ns(task_pid(current)) == pid_active_ns(task_pid(tsk));
> +}
> +
>  static int pid_in_pid_ns(struct pid *pid, struct pid_namespace *ns)
>  {
>  	return pid && (ns->level <= pid->level) &&
> Index: 2.6.23-mm1/kernel/signal.c
> ===================================================================
> --- 2.6.23-mm1.orig/kernel/signal.c	2007-10-27 08:50:51.000000000 -0700
> +++ 2.6.23-mm1/kernel/signal.c	2007-10-27 10:02:04.000000000 -0700
> @@ -679,6 +679,20 @@ static void handle_stop_signal(int sig, 
>  	}
>  }
>  
> +static void masquerade_sender(struct task_struct *t, struct sigqueue *q)
> +{
> +       /*
> +        * If the sender does not have a pid_t in the receiver's active
> +        * pid namespace, set si_pid to 0 and pretend signal originated
> +        * from the kernel.
> +        */
> +       if (!pid_ns_equal(t)) {
> +               q->info.si_pid = 0;
> +               q->info.si_uid = 0;
> +               q->info.si_code = SI_KERNEL;
> +       }
> +}
> +
>  static int send_signal(int sig, struct siginfo *info, struct task_struct *t,
>  			struct sigpending *signals)
>  {
> @@ -730,6 +744,7 @@ static int send_signal(int sig, struct s
>  			copy_siginfo(&q->info, info);
>  			break;
>  		}
> +		masquerade_sender(t, q);
>  	} else if (!is_si_special(info)) {
>  		if (sig >= SIGRTMIN && info->si_code != SI_USER)
>  		/*
> Index: 2.6.23-mm1/include/linux/pid_namespace.h
> ===================================================================
> --- 2.6.23-mm1.orig/include/linux/pid_namespace.h	2007-10-27 09:44:25.000000000 -0700
> +++ 2.6.23-mm1/include/linux/pid_namespace.h	2007-10-27 10:04:20.000000000 -0700
> @@ -56,6 +56,7 @@ static inline struct task_struct *task_c
>  	return tsk->nsproxy->pid_ns->child_reaper;
>  }
>  
> +extern int pid_ns_equal(struct task_struct *tsk);
>  extern int task_in_pid_ns(struct task_struct *tsk, struct pid_namespace *ns);
>  
>  #endif /* _LINUX_PID_NS_H */
>