linux-kernel - Re: [PATCH 7/16] Helpers to find the task by its numerical ids

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Date:	Mon, 9 Jul 2007 21:00:45 -0700
From:	sukadev@...ibm.com
To:	Pavel Emelianov <xemul@...nvz.org>
Cc:	Andrew Morton <akpm@...l.org>, Serge Hallyn <serue@...ibm.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Linux Containers <containers@...ts.osdl.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Kirill Korotaev <dev@...nvz.org>
Subject: Re: [PATCH 7/16] Helpers to find the task by its numerical ids

Pavel Emelianov [xemul@...nvz.org] wrote:
| When searching the task by numerical id on may need to find
| it using global pid (as it is done now in kernel) or by its
| virtual id, e.g. when sending a signal to a task from one
| namespace the sender will specify the task's virtual id.
| 
| Signed-off-by: Pavel Emelianov <xemul@...nvz.org>
| 
| ---
| 
|  fs/proc/base.c        |    2 +-
|  include/linux/pid.h   |   13 +++++++++++--
|  include/linux/sched.h |   31 +++++++++++++++++++++++++++++--
|  kernel/pid.c          |   32 +++++++++++++++++---------------
|  4 files changed, 58 insertions(+), 20 deletions(-)
| 
| --- ./fs/proc/base.c.ve6	2007-07-06 10:58:56.000000000 +0400
| +++ ./fs/proc/base.c	2007-07-06 11:03:41.000000000 +0400
| @@ -2230,7 +2230,7 @@ static struct task_struct *next_tgid(uns
|  	rcu_read_lock();
|  retry:
|  	task = NULL;
| -	pid = find_ge_pid(tgid);
| +	pid = find_ge_pid(tgid, &init_pid_ns);
|  	if (pid) {
|  		tgid = pid->nr + 1;
|  		task = pid_task(pid, PIDTYPE_PID);
| --- ./include/linux/pid.h.ve6	2007-07-06 11:03:27.000000000 +0400
| +++ ./include/linux/pid.h	2007-07-06 11:03:27.000000000 +0400
| @@ -98,14 +98,23 @@ extern struct pid_namespace init_pid_ns;
|  /*
|   * look up a PID in the hash table. Must be called with the tasklist_lock
|   * or rcu_read_lock() held.
| + *
| + * find_pid_ns() finds the pid in the namespace specified
| + * find_pid() find the pid by its global id, i.e. in the init namespace
| + * find_vpid() finr the pid by its virtual id, i.e. in the current namespace
| + *
| + * see also find_task_by_pid() set in include/linux/sched.h
|   */
| -extern struct pid *FASTCALL(find_pid(int nr));
| +extern struct pid *FASTCALL(find_pid_ns(int nr, struct pid_namespace *ns));
| +
| +#define find_vpid(pid)	find_pid_ns(pid, current->nsproxy->pid_ns)
| +#define find_pid(pid)	find_pid_ns(pid, &init_pid_ns)

Adding a second interface maybe more confusing to drivers and non-pid
users.

But more importantly, modifying find_pid() to refer to only init_pid_ns
would require auditing existing find_pid() callers and switching them to
find_vpid().

For instance if capset() is called from a child pid namespace, the 'pid'
would refer to the pid or pgid from child pid ns. But cap_set_pg() calls
find_pid() which gets the number from init_pid_ns.

Is there a similar issue with sunos_killpg() ?
-
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