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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: Jens Axboe , Tejun Heo Cc: 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> <34a8c4a7-a58d-63fc-4599-accf1cbb6aae@redhat.com> <5fbaea42-14a7-27a8-cea1-3a59161ceba0@kernel.dk> From: Waiman Long In-Reply-To: <5fbaea42-14a7-27a8-cea1-3a59161ceba0@kernel.dk> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.1 on 10.11.54.7 X-Rspamd-Queue-Id: 6754280020 X-Stat-Signature: yiju9id91nzuj8ycddah8h9aqq6tpqg5 X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1671036934-427292 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 12/14/22 11:54, Jens Axboe wrote: > On 12/13/22 12:53 PM, Waiman Long wrote: >> 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(). > Since the other one also needs an edit, would be great if you could > just send out a v4. > Sure, will do that. Cheers, Longman