Eric W. Biederman wrote:
> Implement a simple check to see if a specified pid resides
> in a specified pid namespace.  Generally we are smart enough
> just to operate on single pid namespace and avoid this test.
> However in the case of sending a signal to init we must check
> to see if our sender is a child of init and so this test is needed.
> 
> Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
> ---
>  include/linux/pid.h |    3 +++
>  kernel/pid.c        |    6 ++++++
>  2 files changed, 9 insertions(+), 0 deletions(-)
> 
> diff --git a/include/linux/pid.h b/include/linux/pid.h
> index c4b56c0..e409cc5 100644
> --- a/include/linux/pid.h
> +++ b/include/linux/pid.h
> @@ -156,6 +156,9 @@ static inline pid_t pid_nr(struct pid *pid)
>  pid_t pid_nr_ns(struct pid *pid, struct pid_namespace *ns);
>  pid_t pid_vnr(struct pid *pid);
>  
> +/* Test to see if pid is present in pid namespace ns */
> +extern int pid_in_pid_ns(struct pid *pid, struct pid_namespace *ns);
> +
>  #define do_each_pid_task(pid, type, task)				\
>  	do {								\
>  		struct hlist_node *pos___;				\
> diff --git a/kernel/pid.c b/kernel/pid.c
> index a7ecfce..873c00f 100644
> --- a/kernel/pid.c
> +++ b/kernel/pid.c
> @@ -429,6 +429,12 @@ struct pid *find_get_pid(pid_t nr)
>  	return pid;
>  }
>  
> +int pid_in_pid_ns(struct pid *pid, struct pid_namespace *ns)

Can we give it a better name? Like pid_in_ns() if we do want it
to be as short as possible, or pid_visible_in_ns() if we want
it ti reflect its nature.

> +{
> +	return pid && ns && (ns->level <= pid->level) &&
> +		pid->numbers[ns->level].ns == ns;
> +}
> +
>  pid_t pid_nr_ns(struct pid *pid, struct pid_namespace *ns)
>  {
>  	struct upid *upid;

Thanks,
Pavel
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