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bh=JQg3oq06Uw+1wG32ld/l34XBIlmOl7KcZS/r8y8eH90=; b=BNOOOfQqNCwnIVq5uI1Gv6r+0NBA2km1aEquWDKmN4DNp7r+/v11I1OPj3bGw6cdDIQEpU 1TOr/FBSkY210y0yAYAfKtD9T9M8YrAaZcti41LBW9f7Z3YgU9izwICJ/C602IYdW44erP SBAdBBFAT/9pC3hP+W6Oj3Snax2UcRc= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-529-vK79Q7I0O6SEt1SJkCSsgA-1; Wed, 14 Dec 2022 22:31:45 -0500 X-MC-Unique: vK79Q7I0O6SEt1SJkCSsgA-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.rdu2.redhat.com [10.11.54.2]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 35F9B811E9C; Thu, 15 Dec 2022 03:31:45 +0000 (UTC) Received: from llong.com (unknown [10.22.16.55]) by smtp.corp.redhat.com (Postfix) with ESMTP id A624640ED76E; Thu, 15 Dec 2022 03:31:44 +0000 (UTC) From: Waiman Long To: Jens Axboe , Tejun Heo , Josef Bacik , Zefan Li , Johannes Weiner , Andrew Morton Cc: cgroups@vger.kernel.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, =?utf-8?q?Michal_Koutn?= =?utf-8?q?=C3=BD?= , "Dennis Zhou (Facebook)" , Waiman Long , Yi Zhang Subject: [PATCH v4 1/2] bdi, blk-cgroup: Fix potential UAF of blkcg Date: Wed, 14 Dec 2022 22:31:31 -0500 Message-Id: <20221215033132.230023-2-longman@redhat.com> In-Reply-To: <20221215033132.230023-1-longman@redhat.com> References: <20221215033132.230023-1-longman@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.2 X-Rspam-User: X-Rspamd-Queue-Id: 9B4D34000D X-Rspamd-Server: rspam01 X-Stat-Signature: wocpungp4i8gqk9319bimnm1wnmrd313 X-HE-Tag: 1671075114-846014 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: 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. [ 34.254240] RIP: 0010:blkcg_destroy_blkgs+0x16a/0x1a0 : [ 34.339943] Call Trace: [ 34.344510] blkcg_unpin_online+0x38/0x60 [ 34.348523] cgwb_release_workfn+0x6a/0x200 [ 34.352708] process_one_work+0x1e5/0x3b0 [ 34.360758] worker_thread+0x50/0x3a0 [ 34.368447] kthread+0xd9/0x100 [ 34.376386] ret_from_fork+0x22/0x30 This confirms that a potential UAF situation can really happen in cgwb_release_workfn(). Fix that by delaying the css_put() until after the blkcg_unpin_online() call. Also use percpu_ref_is_zero() in blkcg_destroy_blkgs() and issue a warning if reference count is zero. The reproducing system can no longer produce a warning with this patch. All the runnable block/0* tests including block/027 were run successfully without failure. Fixes: 59b57717fff8 ("blkcg: delay blkg destruction until after writeback has finished") Suggested-by: Michal Koutný Reported-by: Yi Zhang Signed-off-by: Waiman Long Acked-by: Tejun Heo --- block/blk-cgroup.c | 7 +++++++ mm/backing-dev.c | 8 ++++++-- 2 files changed, 13 insertions(+), 2 deletions(-) diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c index 1bb939d3b793..ca28306aa1b1 100644 --- a/block/blk-cgroup.c +++ b/block/blk-cgroup.c @@ -1084,6 +1084,13 @@ struct list_head *blkcg_get_cgwb_list(struct cgroup_subsys_state *css) */ static void blkcg_destroy_blkgs(struct blkcg *blkcg) { + /* + * blkcg_destroy_blkgs() shouldn't be called with all the blkcg + * references gone. + */ + if (WARN_ON_ONCE(percpu_ref_is_zero(&blkcg->css.refcnt))) + return; + might_sleep(); spin_lock_irq(&blkcg->lock); diff --git a/mm/backing-dev.c b/mm/backing-dev.c index c30419a5e119..36f75b072325 100644 --- a/mm/backing-dev.c +++ b/mm/backing-dev.c @@ -390,11 +390,15 @@ static void cgwb_release_workfn(struct work_struct *work) wb_shutdown(wb); css_put(wb->memcg_css); - css_put(wb->blkcg_css); mutex_unlock(&wb->bdi->cgwb_release_mutex); - /* triggers blkg destruction if no online users left */ + /* + * Triggers blkg destruction if no online users left + * The final blkcg css_put() has to be done after blkcg_unpin_online() + * to avoid use-after-free. + */ blkcg_unpin_online(wb->blkcg_css); + css_put(wb->blkcg_css); fprop_local_destroy_percpu(&wb->memcg_completions);