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.
Reported-by: Jason Baron <jbaron@xxxxxxxxxx>
Signed-off-by: Miroslav Benes <mbenes@xxxxxxx>
---
Changes v1->v2:
- Add (patch != klp_transition_patch) check to critical sections and
move the locking to sysfs callbacks (Petr)
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;
}
--
2.15.1
--
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