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

From: Baptiste Lepers
Date: Sun Sep 05 2021 - 21:53:25 EST

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

Signed-off-by: Baptiste Lepers <baptiste.lepers@xxxxxxxxx>
Fixes: 375637bc52495 ("perf/core: Introduce address range filtering")
kernel/events/core.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 744e8726c5b2..0c000cb01eeb 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -10193,7 +10193,7 @@ static void perf_event_addr_filters_apply(struct perf_event *event)

if (ifh->nr_file_filters) {
- mm = get_task_mm(event->ctx->task);
+ mm = get_task_mm(task);
if (!mm)
goto restart;