linux-kernel - [PATCH 06/11] pidns: Don't allow new processes in a dead pid namespace.

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Date:	Fri, 16 Nov 2012 08:35:45 -0800
From:	"Eric W. Biederman" <ebiederm@...ssion.com>
To:	Linux Containers <containers@...ts.linux-foundation.org>
Cc:	<linux-kernel@...r.kernel.org>, Oleg Nesterov <oleg@...sign.ru>,
	Serge Hallyn <serge@...lyn.com>,
	Gao feng <gaofeng@...fujitsu.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: [PATCH 06/11] pidns: Don't allow new processes in a dead pid namespace.

From: "Eric W. Biederman" <ebiederm@...ssion.com>

Set nr_hashed to -1 just before we schedule the work to cleanup proc.
Test nr_hashed just before we hash a new pid and if nr_hashed is < 0
fail.

This guaranteees that processes never enter a pid namespaces after we
have cleaned up the state to support processes in a pid namespace.

Currently sending SIGKILL to all of the process in a pid namespace as
init exists gives us this guarantee but we need something a little
stronger to support unsharing and joining a pid namespace.

Acked-by: "Serge E. Hallyn" <serge@...lyn.com>
Signed-off-by: Eric W. Biederman <ebiederm@...ssion.com>
---
 kernel/pid.c |    8 +++++++-
 1 files changed, 7 insertions(+), 1 deletions(-)

diff --git a/kernel/pid.c b/kernel/pid.c
index e957f8b..9c21911 100644
--- a/kernel/pid.c
+++ b/kernel/pid.c
@@ -274,8 +274,10 @@ void free_pid(struct pid *pid)
 	for (i = 0; i <= pid->level; i++) {
 		struct upid *upid = pid->numbers + i;
 		hlist_del_rcu(&upid->pid_chain);
-		if (--upid->ns->nr_hashed == 0)
+		if (--upid->ns->nr_hashed == 0) {
+			upid->ns->nr_hashed = -1;
 			schedule_work(&upid->ns->proc_work);
+		}
 	}
 	spin_unlock_irqrestore(&pidmap_lock, flags);
 
@@ -321,6 +323,8 @@ struct pid *alloc_pid(struct pid_namespace *ns)
 
 	upid = pid->numbers + ns->level;
 	spin_lock_irq(&pidmap_lock);
+	if (ns->nr_hashed < 0)
+		goto out_unlock;
 	for ( ; upid >= pid->numbers; --upid) {
 		hlist_add_head_rcu(&upid->pid_chain,
 				&pid_hash[pid_hashfn(upid->nr, upid->ns)]);
@@ -331,6 +335,8 @@ struct pid *alloc_pid(struct pid_namespace *ns)
 out:
 	return pid;
 
+out_unlock:
+	spin_unlock(&pidmap_lock);
 out_free:
 	while (++i <= ns->level)
 		free_pidmap(pid->numbers + i);
-- 
1.7.5.4

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