linux-kernel - [PATCH] nsproxy: Fix ->nsproxy counting problem in copy

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Date:	Thu, 07 Mar 2013 15:42:41 +0600
From:	Rakib Mullick <rakib.mullick@...il.com>
To:	linux-kernel@...r.kernel.org
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Serge Hallyn <serge.hallyn@...onical.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: [PATCH] nsproxy: Fix ->nsproxy counting problem in copy_namespace.

>From cd41495e25cf2641ffe9e01a40d3d221a46b08be Mon Sep 17 00:00:00 2001
From: Rakib Mullick <rakib.mullick@...il.com>
Date: Thu, 7 Mar 2013 14:52:20 +0600
Subject: [PATCH] nsproxy: Fix ->nsproxy counting problem in copy_namespace.

In copy_namespace(), get_nsproxy() (which increments nsproxy->count) is called before checking namespace related flags.
Therefore, task's nsproxy->count could have improper value, which could lead to calling free_nsproxy unnecessarily. Also,
incrementing nsproxy->count is an atomic operation (which is expensive than normal increment operation), so before
doing it - it's better we make sure namespace related flags are set.

Signed-off-by: Rakib Mullick <rakib.mullick@...il.com>
---
 kernel/nsproxy.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/nsproxy.c b/kernel/nsproxy.c
index afc0456..de36209 100644
--- a/kernel/nsproxy.c
+++ b/kernel/nsproxy.c
@@ -130,12 +130,12 @@ int copy_namespaces(unsigned long flags, struct task_struct *tsk)
 	if (!old_ns)
 		return 0;
 
-	get_nsproxy(old_ns);
-
 	if (!(flags & (CLONE_NEWNS | CLONE_NEWUTS | CLONE_NEWIPC |
 				CLONE_NEWPID | CLONE_NEWNET)))
 		return 0;
 
+	get_nsproxy(old_ns);
+
 	if (!ns_capable(user_ns, CAP_SYS_ADMIN)) {
 		err = -EPERM;
 		goto out;
-- 
1.7.11.7



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