From bb84e79f4f794277545f69348c3e906a6b5a5c85 Mon Sep 17 00:00:00 2001
From: Baptiste Lepers <baptiste.lepers@gmail.com>
Date: Mon, 6 Sep 2021 11:53:10 +1000
Subject: [PATCH] events: Reuse value read using READ_ONCE instead of re-reading it
Git-commit: b89a05b21f46150ac10a962aa50109250b56b03b
Patch-mainline: v5.15-rc2
References: stable-5.14.7

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: 375637bc52495 ("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>
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 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 1cb1f9b8392e..e5c4aca620c5 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -10192,7 +10192,7 @@ 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;
 
-- 
2.26.2