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: 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>

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 7615a97a3511dc770686eccc7dc9d2622aafd2ff..e56a74fd5c814fa1535d18d2cf3e09e56b2c232e 100644 (file)
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -8115,7 +8115,7 @@ static void perf_event_addr_filters_apply(struct perf_event *event)
        if (task == TASK_TOMBSTONE)
                return;
 
-       mm = get_task_mm(event->ctx->task);
+       mm = get_task_mm(task);
        if (!mm)
                goto restart;