[PATCH] pid: Extend/Fix pid_vnr

[PATCH] pid: Extend/Fix pid_vnr

[Eric W. Biederman]

pid_vnr returns the user space pid with respect to the pid namespace
the struct pid was allocated in.  What we want before we return a pid
to user space is the user space pid with respect to the pid namespace
of current.

pid_vnr is a very nice optimization but because it isn't quite what we
want it is easy to use pid_vnr at times when we aren't certain the
struct pid was allocated in our pid namespace.

Currently this describes at least tiocgpgrp and tiocgsid in ttyio.c
the parent process reported in the core dumps and the parent
process in get_signal_to_deliver.

So unless the performance impact is huge having an interface that does
what we want instead of always what we want should be much more
reliable and much less error prone.

Signed-off-by: Eric W. Biederman <ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org>
---
 include/linux/pid.h   |   14 +++-----------
 include/linux/sched.h |    5 ++---
 kernel/pid.c          |    6 ++++++
 3 files changed, 11 insertions(+), 14 deletions(-)

diff --git a/include/linux/pid.h b/include/linux/pid.h
index 061abb6..b91f473 100644
--- a/include/linux/pid.h
+++ b/include/linux/pid.h
@@ -127,9 +127,8 @@ extern void FASTCALL(free_pid(struct pid *pid));
  * the helpers to get the pid's id seen from different namespaces
  *
  * pid_nr()    : global id, i.e. the id seen from the init namespace;
- * pid_vnr()   : virtual id, i.e. the id seen from the namespace this pid
- *               belongs to. this only makes sence when called in the
- *               context of the task that belongs to the same namespace;
+ * pid_vnr()   : virtual id, i.e. the id seen from the pid namespace of
+ *               current.
  * pid_nr_ns() : id seen from the ns specified.
  *
  * see also task_xid_nr() etc in include/linux/sched.h
@@ -144,14 +143,7 @@ static inline pid_t pid_nr(struct pid *pid)
 }
 
 pid_t pid_nr_ns(struct pid *pid, struct pid_namespace *ns);
-
-static inline pid_t pid_vnr(struct pid *pid)
-{
-	pid_t nr = 0;
-	if (pid)
-		nr = pid->numbers[pid->level].nr;
-	return nr;
-}
+pid_t pid_vnr(struct pid *pid);
 
 #define do_each_pid_task(pid, type, task)				\
 	do {								\
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 1b1e25b..9293114 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1286,9 +1286,8 @@ struct pid_namespace;
  * from various namespaces
  *
  * task_xid_nr()     : global id, i.e. the id seen from the init namespace;
- * task_xid_vnr()    : virtual id, i.e. the id seen from the namespace the task
- *                     belongs to. this only makes sence when called in the
- *                     context of the task that belongs to the same namespace;
+ * task_xid_vnr()    : virtual id, i.e. the id seen from the pid namespace of
+ *                     current.
  * task_xid_nr_ns()  : id seen from the ns specified;
  *
  * set_task_vxid()   : assigns a virtual id to a task;
diff --git a/kernel/pid.c b/kernel/pid.c
index 21f027c..c507ca7 100644
--- a/kernel/pid.c
+++ b/kernel/pid.c
@@ -442,6 +442,12 @@ pid_t pid_nr_ns(struct pid *pid, struct pid_namespace *ns)
 	return nr;
 }
 
+pid_t pid_vnr(struct pid *pid)
+{
+	return pid_nr_ns(pid, current->nsproxy->pid_ns);
+}
+EXPORT_SYMBOL_GPL(pid_vnr);
+
 pid_t task_pid_nr_ns(struct task_struct *tsk, struct pid_namespace *ns)
 {
 	return pid_nr_ns(task_pid(tsk), ns);
-- 
1.5.3.rc6.17.g1911

Re: [PATCH] pid: Extend/Fix pid_vnr

[Pavel Emelyanov]

Eric W. Biederman wrote:
> pid_vnr returns the user space pid with respect to the pid namespace
> the struct pid was allocated in.  What we want before we return a pid
> to user space is the user space pid with respect to the pid namespace
> of current.
> 
> pid_vnr is a very nice optimization but because it isn't quite what we
> want it is easy to use pid_vnr at times when we aren't certain the
> struct pid was allocated in our pid namespace.
> 
> Currently this describes at least tiocgpgrp and tiocgsid in ttyio.c
> the parent process reported in the core dumps and the parent
> process in get_signal_to_deliver.
> 
> So unless the performance impact is huge having an interface that does
> what we want instead of always what we want should be much more
> reliable and much less error prone.
> 
> Signed-off-by: Eric W. Biederman <ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org>

Yup. xxx_vnr with the existing meaning turns out to be useless.

Thanks, Eric.

Acked-by: Pavel Emelyanov <xemul-GEFAQzZX7r8dnm+yROfE0A@public.gmane.org>

> ---
>  include/linux/pid.h   |   14 +++-----------
>  include/linux/sched.h |    5 ++---
>  kernel/pid.c          |    6 ++++++
>  3 files changed, 11 insertions(+), 14 deletions(-)
> 
> diff --git a/include/linux/pid.h b/include/linux/pid.h
> index 061abb6..b91f473 100644
> --- a/include/linux/pid.h
> +++ b/include/linux/pid.h
> @@ -127,9 +127,8 @@ extern void FASTCALL(free_pid(struct pid *pid));
>   * the helpers to get the pid's id seen from different namespaces
>   *
>   * pid_nr()    : global id, i.e. the id seen from the init namespace;
> - * pid_vnr()   : virtual id, i.e. the id seen from the namespace this pid
> - *               belongs to. this only makes sence when called in the
> - *               context of the task that belongs to the same namespace;
> + * pid_vnr()   : virtual id, i.e. the id seen from the pid namespace of
> + *               current.
>   * pid_nr_ns() : id seen from the ns specified.
>   *
>   * see also task_xid_nr() etc in include/linux/sched.h
> @@ -144,14 +143,7 @@ static inline pid_t pid_nr(struct pid *pid)
>  }
>  
>  pid_t pid_nr_ns(struct pid *pid, struct pid_namespace *ns);
> -
> -static inline pid_t pid_vnr(struct pid *pid)
> -{
> -	pid_t nr = 0;
> -	if (pid)
> -		nr = pid->numbers[pid->level].nr;
> -	return nr;
> -}
> +pid_t pid_vnr(struct pid *pid);
>  
>  #define do_each_pid_task(pid, type, task)				\
>  	do {								\
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 1b1e25b..9293114 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -1286,9 +1286,8 @@ struct pid_namespace;
>   * from various namespaces
>   *
>   * task_xid_nr()     : global id, i.e. the id seen from the init namespace;
> - * task_xid_vnr()    : virtual id, i.e. the id seen from the namespace the task
> - *                     belongs to. this only makes sence when called in the
> - *                     context of the task that belongs to the same namespace;
> + * task_xid_vnr()    : virtual id, i.e. the id seen from the pid namespace of
> + *                     current.
>   * task_xid_nr_ns()  : id seen from the ns specified;
>   *
>   * set_task_vxid()   : assigns a virtual id to a task;
> diff --git a/kernel/pid.c b/kernel/pid.c
> index 21f027c..c507ca7 100644
> --- a/kernel/pid.c
> +++ b/kernel/pid.c
> @@ -442,6 +442,12 @@ pid_t pid_nr_ns(struct pid *pid, struct pid_namespace *ns)
>  	return nr;
>  }
>  
> +pid_t pid_vnr(struct pid *pid)
> +{
> +	return pid_nr_ns(pid, current->nsproxy->pid_ns);
> +}
> +EXPORT_SYMBOL_GPL(pid_vnr);
> +
>  pid_t task_pid_nr_ns(struct task_struct *tsk, struct pid_namespace *ns)
>  {
>  	return pid_nr_ns(task_pid(tsk), ns);

Re: [PATCH] pid: Extend/Fix pid_vnr

[Oleg Nesterov]

On 12/05, Eric W. Biederman wrote:
> 
> +pid_t pid_vnr(struct pid *pid)
> +{
> +	return pid_nr_ns(pid, current->nsproxy->pid_ns);
> +}

Excellent!!!

This allows us to do many cleanups. I am sending the trivial patch just
as example.

Oleg.

Re: [PATCH] pid: Extend/Fix pid_vnr

[sukadev-r/Jw6+rmf7HQT0dZR+AlfA]

Oleg Nesterov [oleg-6lXkIZvqkOAvJsYlp49lxw@public.gmane.org] wrote:
| On 12/05, Eric W. Biederman wrote:
| > 
| > +pid_t pid_vnr(struct pid *pid)
| > +{
| > +	return pid_nr_ns(pid, current->nsproxy->pid_ns);
| > +}

Hmm. current->nsproxy be NULL during process exit ?
So this safe as long as pid_vnr() is not called after a
process exits its namespaces. Probably no such callers atm. 

| 
| Excellent!!!
| 
| This allows us to do many cleanups. I am sending the trivial patch just
| as example.
| 
| Oleg.

Re: [PATCH] pid: Extend/Fix pid_vnr

[Serge E. Hallyn]

Quoting sukadev-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org (sukadev-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org):
> Oleg Nesterov [oleg-6lXkIZvqkOAvJsYlp49lxw@public.gmane.org] wrote:
> | On 12/05, Eric W. Biederman wrote:
> | > 
> | > +pid_t pid_vnr(struct pid *pid)
> | > +{
> | > +	return pid_nr_ns(pid, current->nsproxy->pid_ns);
> | > +}
> 
> Hmm. current->nsproxy be NULL during process exit ?
> So this safe as long as pid_vnr() is not called after a
> process exits its namespaces. Probably no such callers atm. 

Yes I did a little audit for those this morning bc I frankly didn't
believe there weren't any.  But I couldn't find any :)

-serge

> | 
> | Excellent!!!
> | 
> | This allows us to do many cleanups. I am sending the trivial patch just
> | as example.
> | 
> | Oleg.
> _______________________________________________
> Containers mailing list
> Containers-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org
> https://lists.linux-foundation.org/mailman/listinfo/containers

Re: [PATCH] pid: Extend/Fix pid_vnr

[Eric W. Biederman]

"Serge E. Hallyn" <serue-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org> writes:

> Quoting sukadev-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org (sukadev-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org):
>> Oleg Nesterov [oleg-6lXkIZvqkOAvJsYlp49lxw@public.gmane.org] wrote:
>> | On 12/05, Eric W. Biederman wrote:
>> | > 
>> | > +pid_t pid_vnr(struct pid *pid)
>> | > +{
>> | > +	return pid_nr_ns(pid, current->nsproxy->pid_ns);
>> | > +}
>> 
>> Hmm. current->nsproxy be NULL during process exit ?
>> So this safe as long as pid_vnr() is not called after a
>> process exits its namespaces. Probably no such callers atm. 
>
> Yes I did a little audit for those this morning bc I frankly didn't
> believe there weren't any.  But I couldn't find any :)

Cool.  The only case pid_vnr would make sense in that context is if
we were talking to user space after we had exited our namespaces.
Which is at least as stretch.

Eric

[PATCH] sys_getsid: don't use ->nsproxy directly

[Oleg Nesterov]

With the new semantics of find_vpid() we don't need to play with ->nsproxy
explicitely, _vxx() do the right things.

Also s/tasklist/rcu/.

Signed-off-by: Oleg Nesterov <oleg-6lXkIZvqkOAvJsYlp49lxw@public.gmane.org>

--- PT/kernel/sys.c~	2007-12-05 21:43:18.000000000 +0300
+++ PT/kernel/sys.c	2007-12-06 20:09:02.000000000 +0300
@@ -1025,19 +1025,16 @@ asmlinkage long sys_getsid(pid_t pid)
 	else {
 		int retval;
 		struct task_struct *p;
-		struct pid_namespace *ns;
 
-		ns = current->nsproxy->pid_ns;
-
-		read_lock(&tasklist_lock);
-		p = find_task_by_pid_ns(pid, ns);
+		rcu_read_lock();
+		p = find_task_by_vpid(pid);
 		retval = -ESRCH;
 		if (p) {
 			retval = security_task_getsid(p);
 			if (!retval)
-				retval = task_session_nr_ns(p, ns);
+				retval = task_session_vnr(p);
 		}
-		read_unlock(&tasklist_lock);
+		rcu_read_unlock();
 		return retval;
 	}
 }