linux-kernel - Re: [PATCH 2/3] blk-cgroup: fix uaf in blkcg_activate_policy() racing with blkg_free

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Message-Id: <22046287-0a36-45ac-bc17-b41636076552@fnnas.com>
Date: Fri, 9 Jan 2026 14:43:39 +0800
From: "Yu Kuai" <yukuai@...as.com>
To: "Zheng Qixing" <zhengqixing@...weicloud.com>
Cc: <hch@...radead.org>, <cgroups@...r.kernel.org>, 
	<linux-block@...r.kernel.org>, <linux-kernel@...r.kernel.org>, 
	<yi.zhang@...wei.com>, <yangerkun@...wei.com>, <houtao1@...wei.com>, 
	<tj@...nel.org>, <josef@...icpanda.com>, <axboe@...nel.dk>, 
	<zhengqixing@...wei.com>, <yukuai@...as.com>
Subject: Re: [PATCH 2/3] blk-cgroup: fix uaf in blkcg_activate_policy() racing with blkg_free_workfn()

Hi,

在 2026/1/9 14:22, Zheng Qixing 写道:
> I tried adding blkcg_mutex protection in blkcg_activate_policy() and 
> blkg_destroy_all() as suggested.
>
> Unfortunately, the UAF still occurs even with proper mutex protection.
>
> The mutex successfully protects the list structure during traversal 
> won't be added/removed from
>
> q->blkg_list while we hold the lock. However, this doesn't prevent the 
> same blkg from being released
>
> twice.

I don't understand, what I suggested should actually include your changes in this patch. Can you
show your changes and make sure blkcg_policy_teardown_pds() inside blkcg_activate_policy() is
also protected.

-- 
Thansk,
Kuai