events: Reuse value read using READ_ONCE instead of re-reading it

commit b89a05b21f46150ac10a962aa50109250b56b03b upstream.

In perf_event_addr_filters_apply, the task associated with
the event (event->ctx->task) is read using READ_ONCE at the beginning
of the function, checked, and then re-read from event->ctx->task,
voiding all guarantees of the checks. Reuse the value that was read by
READ_ONCE to ensure the consistency of the task struct throughout the
function.

Fixes: aeab82993f45c ("perf/core: Introduce address range filtering")
Signed-off-by: Baptiste Lepers <baptiste.lepers@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20210906015310.12802-1-baptiste.lepers@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 2f848123cdae85556ba666f8e6692043b22ea868..1993a741d2dc5fb1b9977eb61fafb8e143c7c492 100644 (file)
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -9259,7 +9259,7 @@ static void perf_event_addr_filters_apply(struct perf_event *event)
                return;
 
        if (ifh->nr_file_filters) {
-               mm = get_task_mm(event->ctx->task);
+               mm = get_task_mm(task);
                if (!mm)
                        goto restart;