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Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.4.0 Subject: Re: [PATCH-block v3 1/2] bdi, blk-cgroup: Fix potential UAF of blkcg Content-Language: en-US To: Tejun Heo Cc: Jens Axboe , Josef Bacik , Zefan Li , Johannes Weiner , Andrew Morton , cgroups@vger.kernel.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, =?UTF-8?Q?Michal_Koutn=c3=bd?= , "Dennis Zhou (Facebook)" , Yi Zhang References: <20221213184446.50181-1-longman@redhat.com> <20221213184446.50181-2-longman@redhat.com> From: Waiman Long In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 3.1 on 10.11.54.9 X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 5072E4001C X-Stat-Signature: 14du9k3hzrcq9a8c6itjet5pbh65mqgx X-HE-Tag: 1670961243-620691 X-HE-Meta: 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 12/13/22 14:29, Tejun Heo wrote: > On Tue, Dec 13, 2022 at 01:44:45PM -0500, Waiman Long wrote: >> Commit 59b57717fff8 ("blkcg: delay blkg destruction until after >> writeback has finished") delayed call to blkcg_destroy_blkgs() to >> cgwb_release_workfn(). However, it is done after a css_put() of blkcg >> which may be the final put that causes the blkcg to be freed as RCU >> read lock isn't held. >> >> Another place where blkcg_destroy_blkgs() can be called indirectly via >> blkcg_unpin_online() is from the offline_css() function called from >> css_killed_work_fn(). Over there, the potentially final css_put() call >> is issued after offline_css(). >> >> By adding a css_tryget() into blkcg_destroy_blkgs() and warning its >> failure, the following stack trace was produced in a test system on >> bootup. > This doesn't agree with the code anymore. Otherwise > > Acked-by: Tejun Heo Sorry, I overlooked the commit log in my update. I will update it if I need another version, or Jens can make the following edit: css_tryget() -> percpu_ref_is_zero(). Thanks, Longman