On Wed, Dec 21, 2022 at 10:42:39AM +0800, Chengming Zhou wrote: > > Does this help? > > > > diff --git a/kernel/events/core.c b/kernel/events/core.c > > index e47914ac8732..bbff551783e1 100644 > > --- a/kernel/events/core.c > > +++ b/kernel/events/core.c > > @@ -12689,7 +12689,8 @@ SYSCALL_DEFINE5(perf_event_open, > > return event_fd; > > > > err_context: > > - /* event->pmu_ctx freed by free_event() */ > > + put_pmu_ctx(event->pmu_ctx); > > + event->pmu_ctx = NULL; /* _free_event() */ > > err_locked: > > mutex_unlock(&ctx->mutex); > > perf_unpin_context(ctx); > > Tested-by: Chengming Zhou <zhouchengming@xxxxxxxxxxxxx> > > While reviewing the code, I found perf_event_create_kernel_counter() > has the similar problem in the "err_pmu_ctx" error handling path: Right you are, updated the patch, thanks! > CPU0 CPU1 > perf_event_create_kernel_counter() > // inc ctx refcnt > find_get_context(task, event) (1) > > // inc pmu_ctx refcnt > pmu_ctx = find_get_pmu_context() > > event->pmu_ctx = pmu_ctx > ... > goto err_pmu_ctx: > // dec pmu_ctx refcnt > put_pmu_ctx(pmu_ctx) (2) > > mutex_unlock(&ctx->mutex) > // dec ctx refcnt > put_ctx(ctx) > perf_event_exit_task_context() > mutex_lock() > mutex_unlock() > // last refcnt put > put_ctx() > free_event(event) > if (event->pmu_ctx) // True > put_pmu_ctx() (3) > // will access freed pmu_ctx or ctx > > if (event->ctx) // False > put_ctx() This doesn't look right; iirc you can hit this without concurrency, something like so: // note that when getting here, we've not passed // perf_install_in_context() and event->ctx == NULL. err_pmu_ctx: put_pmu_ctx(); put_ctx(); // last, actually frees ctx .. err_alloc: free_event() _free_event() if (event->pmu_ctx) // true, because we forgot to clear put_pmu_ctx() // hits 0 because double put // goes and touch epc->ctx and UaF
