From 8869016d3a58cbe7c31c70f4f008a92122b271c7 Mon Sep 17 00:00:00 2001 From: Miroslav Benes Date: Thu, 21 Dec 2017 14:40:43 +0100 Subject: [PATCH] livepatch: add locking to force and signal functions klp_send_signals() and klp_force_transition() do not acquire klp_mutex, because it seemed to be superfluous. A potential race in klp_send_signals() was harmless and there was nothing in klp_force_transition() which needed to be synchronized. That changed with the addition of klp_forced variable during the review process. There is a small window now, when klp_complete_transition() does not see klp_forced set to true while all tasks have been already transitioned to the target state. module_put() is called and the module can be removed. Acquire klp_mutex in sysfs callback to prevent it. Do the same for the signal sending just to be sure. There is no real downside to that. Fixes: c99a2be790b07 ("livepatch: force transition to finish") Fixes: 43347d56c8d9d ("livepatch: send a fake signal to all blocking tasks") Reported-by: Jason Baron Signed-off-by: Miroslav Benes Reviewed-by: Petr Mladek Acked-by: Josh Poimboeuf Signed-off-by: Jiri Kosina --- kernel/livepatch/core.c | 52 ++++++++++++++++++++++++++----------------------- 1 file changed, 28 insertions(+), 24 deletions(-) diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c index 1c3c9b27c916..8fd8e8f126da 100644 --- a/kernel/livepatch/core.c +++ b/kernel/livepatch/core.c @@ -537,22 +537,24 @@ static ssize_t signal_store(struct kobject *kobj, struct kobj_attribute *attr, int ret; bool val; - patch = container_of(kobj, struct klp_patch, kobj); - - /* - * klp_mutex lock is not grabbed here intentionally. It is not really - * needed. The race window is harmless and grabbing the lock would only - * hold the action back. - */ - if (patch != klp_transition_patch) - return -EINVAL; - ret = kstrtobool(buf, &val); if (ret) return ret; - if (val) - klp_send_signals(); + if (!val) + return count; + + mutex_lock(&klp_mutex); + + patch = container_of(kobj, struct klp_patch, kobj); + if (patch != klp_transition_patch) { + mutex_unlock(&klp_mutex); + return -EINVAL; + } + + klp_send_signals(); + + mutex_unlock(&klp_mutex); return count; } @@ -564,22 +566,24 @@ static ssize_t force_store(struct kobject *kobj, struct kobj_attribute *attr, int ret; bool val; - patch = container_of(kobj, struct klp_patch, kobj); - - /* - * klp_mutex lock is not grabbed here intentionally. It is not really - * needed. The race window is harmless and grabbing the lock would only - * hold the action back. - */ - if (patch != klp_transition_patch) - return -EINVAL; - ret = kstrtobool(buf, &val); if (ret) return ret; - if (val) - klp_force_transition(); + if (!val) + return count; + + mutex_lock(&klp_mutex); + + patch = container_of(kobj, struct klp_patch, kobj); + if (patch != klp_transition_patch) { + mutex_unlock(&klp_mutex); + return -EINVAL; + } + + klp_force_transition(); + + mutex_unlock(&klp_mutex); return count; } -- 2.11.0