Messages in this thread Patch in this message | | | From | Miroslav Benes <> | Subject | [PATCH] livepatch: add locking to force and signal functions | Date | Wed, 20 Dec 2017 10:28:07 +0100 |
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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 to prevent it. Do the same in klp_send_signals() just to be sure. There is no real downside to that.
Reported-by: Jason Baron <jbaron@akamai.com> Signed-off-by: Miroslav Benes <mbenes@suse.cz> --- kernel/livepatch/transition.c | 8 ++++++++ 1 file changed, 8 insertions(+)
diff --git a/kernel/livepatch/transition.c b/kernel/livepatch/transition.c index be5bfa533ee8..3f932ff607cd 100644 --- a/kernel/livepatch/transition.c +++ b/kernel/livepatch/transition.c @@ -625,6 +625,8 @@ void klp_send_signals(void) pr_notice("signaling remaining tasks\n"); + mutex_lock(&klp_mutex); + read_lock(&tasklist_lock); for_each_process_thread(g, task) { if (!klp_patch_pending(task)) @@ -653,6 +655,8 @@ void klp_send_signals(void) } } read_unlock(&tasklist_lock); + + mutex_unlock(&klp_mutex); } /* @@ -671,6 +675,8 @@ void klp_force_transition(void) pr_warn("forcing remaining tasks to the patched state\n"); + mutex_lock(&klp_mutex); + read_lock(&tasklist_lock); for_each_process_thread(g, task) klp_update_patch_state(task); @@ -680,4 +686,6 @@ void klp_force_transition(void) klp_update_patch_state(idle_task(cpu)); klp_forced = true; + + mutex_unlock(&klp_mutex); } -- 2.15.1
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