[PATCH] livepatch: fix race between enabled_store() and klp_unregister_patch()

[Li Bin <huawei.libin@huawei.com>]

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@huawei.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