linux-kernel - [PATCH] livepatch: fix race between enabled_store() and klp_unregister

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Message-ID: <1448855677-8392-1-git-send-email-huawei.libin@huawei.com>
Date:	Mon, 30 Nov 2015 11:54:37 +0800
From:	Li Bin <huawei.libin@...wei.com>
To:	<jpoimboe@...hat.com>, <sjenning@...hat.com>, <jikos@...nel.org>,
	<vojtech@...e.com>
CC:	<live-patching@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<guohanjun@...wei.com>, <dingtianhong@...wei.com>,
	<xiexiuqi@...wei.com>, <zhouchengming1@...wei.com>
Subject: [PATCH] livepatch: fix race between enabled_store() and klp_unregister_patch()

There is a potential race as following:

CPU0                         |  CPU1
-----------------------------|-----------------------------------
enabled_store()              |  klp_unregister_patch()
                             |  |-mutex_lock(&klp_mutex);
|-mutex_lock(&klp_mutex);    |  |-klp_free_patch();
                             |  |-mutex_unlock(&klp_mutex);
|-[process the patch's state]|
|-mutex_unlock(&klp_mutex)   |

Fix this race condition by adding klp_is_patch_registered() check in
enabled_store() after get the lock klp_mutex.

Signed-off-by: Li Bin <huawei.libin@...wei.com>
---
 kernel/livepatch/core.c |    5 +++++
 1 files changed, 5 insertions(+), 0 deletions(-)

diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
index db545cb..50af971 100644
--- a/kernel/livepatch/core.c
+++ b/kernel/livepatch/core.c
@@ -614,6 +614,11 @@ static ssize_t enabled_store(struct kobject *kobj, struct kobj_attribute *attr,
 
 	mutex_lock(&klp_mutex);
 
+	if (!klp_is_patch_registered(patch)) {
+		ret = -EINVAL;
+		goto err;
+	}
+
 	if (val == patch->state) {
 		/* already in requested state */
 		ret = -EINVAL;
-- 
1.7.1

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