On Tue, Mar 06, 2018 at 06:49:10PM +0900, Prashant Bhole wrote: > Sorry for late reply. I tried these changes. It didn't fix the problem. With
He, sorry for completely forgetting about this one :/ > these changes, the use-after-free access of task_struct occurs at > _free_event() for the last remaining event. > > In your changes, I tried keeping get/put_task_struct() in > perf_alloc_context()/put_ctx() intact and The problem did not occur. Changes > are mentioned below. Yes, I think you're right in that this is the cleanest solution; it adds reference counting to the exact pointer we're using. > diff --git a/kernel/events/core.c b/kernel/events/core.c > index c98cce4ceebd..65889d2b5ae2 100644 > --- a/kernel/events/core.c > +++ b/kernel/events/core.c > @@ -4109,6 +4109,8 @@ static void _free_event(struct perf_event *event) > > if (event->ctx) > put_ctx(event->ctx); > + if (event->hw.target) > + put_task_struct(event->hw.target); > > exclusive_event_destroy(event); > module_put(event->pmu->module); > @@ -9593,6 +9595,7 @@ perf_event_alloc(struct perf_event_attr *attr, int > cpu, > * and we cannot use the ctx information because we need the > * pmu before we get a ctx. > */ > + get_task_struct(task); > event->hw.target = task; > } > > @@ -9708,6 +9711,8 @@ perf_event_alloc(struct perf_event_attr *attr, int > cpu, > perf_detach_cgroup(event); > if (event->ns) > put_pid_ns(event->ns); > + if (task) Should this not too be 'event->hw.target', for consistency and clarity? > + put_task_struct(task); > kfree(event); > > return ERR_PTR(err);
