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livepatch: add locking to force and signal functions

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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: c99a2be790 ("livepatch: force transition to finish")
Fixes: 43347d56c8 ("livepatch: send a fake signal to all blocking tasks")
Reported-by: Jason Baron <jbaron@akamai.com>
Signed-off-by: Miroslav Benes <mbenes@suse.cz>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
This commit is contained in:
Miroslav Benes 2017-12-21 14:40:43 +01:00 committed by Jiri Kosina
parent c99a2be790
commit 8869016d3a
1 changed files with 28 additions and 24 deletions
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52
kernel/livepatch/core.c
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@ -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;
}