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bh=+MsWk87quHbEwHCR1sVYteGgGZjHdGBkMWIDf/Jp0nk=; b=hCCgpFcuNCNpZLax9qMCrlOc6ERZDGNA9nU96/psTvhIT9P/EtxGXBmozWXTfqpp5gi4Ts +qZTiH2xQPNuygMjuIOP0E9LNnLNdjglyxjAG6Pj8ME6YlFndHhFhLy6B3WbfaWldN3AN8 e5GuhTs6ln70BBP9A02zAoRaGNvSyqI= 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-658-PtZEtElbO9W4Ys0KShUpYA-1; Thu, 08 Dec 2022 17:01:52 -0500 X-MC-Unique: PtZEtElbO9W4Ys0KShUpYA-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.rdu2.redhat.com [10.11.54.5]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 60E4785A588; Thu, 8 Dec 2022 22:01:51 +0000 (UTC) Received: from llong.com (dhcp-17-153.bos.redhat.com [10.18.17.153]) by smtp.corp.redhat.com (Postfix) with ESMTP id F079E17582; Thu, 8 Dec 2022 22:01:50 +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-block 1/3] bdi, blk-cgroup: Fix potential UAF of blkcg Date: Thu, 8 Dec 2022 17:01:39 -0500 Message-Id: <20221208220141.2625775-2-longman@redhat.com> In-Reply-To: <20221208220141.2625775-1-longman@redhat.com> References: <20221208220141.2625775-1-longman@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.5 X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 877F4A001E X-Rspam-User: X-Stat-Signature: 3sswxxuewttryt6rh4f19jqfbwt8ngoi X-HE-Tag: 1670536918-802565 X-HE-Meta: U2FsdGVkX1+LpBsTDCP50hlkdFS6Ez+kzIyXDstFDBZBba/ymeNXKWx2zv0FXjgo+/IQyC0gyryiaxhvOu5BdqNUecDNEEqDUXNbMkMnSRvsxZyPjWqWCSBcEKWlyoFTOM3u876NM7HoGxE21A+7YdHzs419daxLHSqAfhUKWUzXaMQD3cv6XLCBRvGxVvsKgFSpaaj6wxuCuoLedQyxZWy39GlAGFW6lUrNCGQGnYiYPSZbAZ7Cx/aEjyL4oZwO1I8dp+DOyL825kshyXxBkmJ39QsMHZVu/ezqjOp00XPUpOFHAAX1VtKGLglDO7ey9G17nM1cOzS4VeMVNCRh+0Nbm8HeiRwyj1WDzWLpRjhpWK8mjWBgH8Nn4ohWBSvikdfcxlJPUjrxq4KrTMUlhoPS7w6ls6oWqJHlBOntgl3dR3KJPAWFmoZ1LW5v3V91TxsdQrt2595eJkCC0P3q3EGynBR/204l5IeHQaPTPUuBQCrmgKzMlXfX6vIE4s8nAWUV+IYSBjI/9P0hTpNewfuTmmsUr+GZ8PeBE7jxOiKuBVFSank5t1S3PNUeBldclhbBUUz2CnrhQ2oH56204UuNdWg2oBC+bkZE3qEQVJky9Yn35YGqgBBHXE0LooC3VuSnmVR17glBo+WMcjGRZLiqPNRaW1DpjdnrcOBsVU5a0fw+Ep11H2tQHjW/BPSMuORoZTg4Li0wlgPMxhKXE6YW4PcCc2FVxYlRijjcg3RITaTGI05YTeZC4X2X92m4Kzh2/vT/2SUZB63113L0vnkvmMnZ4l7D9xdyoJYA47WjuuLUINRwpMAsR/wYQIgC18XRuc18ptxkCYo/Nwh3ywhe0Q/D1p5eN+/CbygfzMHuErRE61ItQLeFFsC2WhbX 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 css_tryget() in blkcg_destroy_blkgs() and issue a warning if css_tryget() fails. 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 --- block/blk-cgroup.c | 8 ++++++++ mm/backing-dev.c | 8 ++++++-- 2 files changed, 14 insertions(+), 2 deletions(-) diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c index 1bb939d3b793..21cc88349f21 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(!css_tryget(&blkcg->css))) + return; + might_sleep(); spin_lock_irq(&blkcg->lock); @@ -1110,6 +1117,7 @@ static void blkcg_destroy_blkgs(struct blkcg *blkcg) } spin_unlock_irq(&blkcg->lock); + css_put(&blkcg->css); } /** 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);