From e76946110137703c16423baf6ee177b751a34b7e Mon Sep 17 00:00:00 2001
From: Lai Jiangshan <jiangshan.ljs@antgroup.com>
Date: Thu, 23 Jan 2025 16:25:35 +0800
Subject: [PATCH] workqueue: Put the pwq after detaching the rescuer from the
pool
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The commit 68f83057b913("workqueue: Reap workers via kthread_stop() and
remove detach_completion") adds code to reap the normal workers but
mistakenly does not handle the rescuer and also removes the code waiting
for the rescuer in put_unbound_pool(), which caused a use-after-free bug
reported by Cheung Wall.
To avoid the use-after-free bug, the pool’s reference must be held until
the detachment is complete. Therefore, move the code that puts the pwq
after detaching the rescuer from the pool.
Reported-by: cheung wall <zzqq0103.hey@gmail.com>
Cc: cheung wall <zzqq0103.hey@gmail.com>
Link: https://lore.kernel.org/lkml/CAKHoSAvP3iQW+GwmKzWjEAOoPvzeWeoMO0Gz7Pp3_4kxt-RMoA@mail.gmail.com/
Fixes: 68f83057b913("workqueue: Reap workers via kthread_stop() and remove detach_completion")
Signed-off-by: Lai Jiangshan <jiangshan.ljs@antgroup.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
---
kernel/workqueue.c | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 33a23c7b2274..ccad33001c58 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -3516,12 +3516,6 @@ repeat:
}
}
- /*
- * Put the reference grabbed by send_mayday(). @pool won't
- * go away while we're still attached to it.
- */
- put_pwq(pwq);
-
/*
* Leave this pool. Notify regular workers; otherwise, we end up
* with 0 concurrency and stalling the execution.
@@ -3532,6 +3526,12 @@ repeat:
worker_detach_from_pool(rescuer);
+ /*
+ * Put the reference grabbed by send_mayday(). @pool might
+ * go away any time after it.
+ */
+ put_pwq_unlocked(pwq);
+
raw_spin_lock_irq(&wq_mayday_lock);
}