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Tue, 13 Dec 2022 11:29:28 -0800 (PST) Received: from localhost ([2620:10d:c090:400::5:c415]) by smtp.gmail.com with ESMTPSA id c197-20020a624ece000000b005745788f44csm8017095pfb.124.2022.12.13.11.29.27 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 13 Dec 2022 11:29:27 -0800 (PST) Date: Tue, 13 Dec 2022 09:29:26 -1000 From: Tejun Heo To: Waiman Long 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, Michal =?iso-8859-1?Q?Koutn=FD?= , "Dennis Zhou (Facebook)" , Yi Zhang Subject: Re: [PATCH-block v3 1/2] bdi, blk-cgroup: Fix potential UAF of blkcg Message-ID: References: <20221213184446.50181-1-longman@redhat.com> <20221213184446.50181-2-longman@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20221213184446.50181-2-longman@redhat.com> X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 8538E40011 X-Stat-Signature: i7mcxd93bouthewjdbysitz3tskm6qze X-HE-Tag: 1670959769-11380 X-HE-Meta: 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 wx8DLEK1 u+vQOEztC+Zw2IuJrXvIGwnht1sK7qJnHeqUb6zcSTvgxAdDnxhdsbiV3sVw9NqbtxDhCi4WhGClYI3LU3HRUIs4I/jjgJMXeuC6YkeM3qUQABnIIuBJqBTkD9vmie5x50GAAFcC0ICOJCKnLyrQQl9r05YwrryOPz4jPQE0Ej/BwVRCUhzKUMpCuTZomhU1jX/MfZbzuk186iv+jloLRnaph+MPU7YVAVRZHrmlnP5JKmzTPSUdk8+0C3A== 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 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 Thanks. -- tejun