From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 85C2E33F8AA; Mon, 20 Apr 2026 16:05:59 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776701159; cv=none; b=dfW+K+Y0jNKcW/IvMAhr+abiAr4wMSDxllMZThtsrKomGwqm+X4d2Rb8+K+jTw7l7o2Y5YhKiaPFsnqOWnoel74SgHbeT3/oP4mPDnGGnYWijNd6tKxqiEhn8eE6YrbMFvCb/zFWtclLIOixR2ReFAA1GvNyAmdHBc3goCdqHdw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776701159; c=relaxed/simple; bh=QilLMZPx7+Ca/3lpCu9Of9U4ZmBuGrlro6d3e8VGMdU=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=c+sbbCIzpiP4GPl+5Rlp5YZohZ4vMxRtFB5PjS7js2PDC6C5nlQYcIM6OlSlD73Fq8L5/JDGRXOg57sc/G33ED4wDwnjvUkResqq+ddY0F0hx/0x1JNoF6nwbu9yHK+sWGZo5vUom+zD1aETFl6BZ5md6KyCBGV0eQLDL7IavA4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=Oyi0lh47; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="Oyi0lh47" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E8F30C2BCB4; Mon, 20 Apr 2026 16:05:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1776701159; bh=QilLMZPx7+Ca/3lpCu9Of9U4ZmBuGrlro6d3e8VGMdU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Oyi0lh47ehHQuqHQKz6JWBUQgJL9D0DMvy0GTAKmOP7HrXeCx624p884vmzCJZUn5 mom1vRVBIYv29AEGghTEeaa69JpUTTphR8qVb8h1QYBOCj1M86+M/24meSKrmUTcvF Fx3XC0crit3FUAklXXwf4BWFGeCBalqrQHwo9bI4= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Breno Leitao , Dennis Zhou , Shakeel Butt , David Hildenbrand , Jens Axboe , Johannes Weiner , Josef Bacik , JP Kobryn , Liam Howlett , "Lorenzo Stoakes (Oracle)" , Martin KaFai Lau , Michal Hocko , Mike Rapoport , Suren Baghdasaryan , Tejun Heo , Andrew Morton Subject: [PATCH 6.18 184/198] mm: blk-cgroup: fix use-after-free in cgwb_release_workfn() Date: Mon, 20 Apr 2026 17:42:43 +0200 Message-ID: <20260420153942.240981125@linuxfoundation.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260420153935.605963767@linuxfoundation.org> References: <20260420153935.605963767@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Breno Leitao commit 8f5857be99f1ed1fa80991c72449541f634626ee upstream. cgwb_release_workfn() calls css_put(wb->blkcg_css) and then later accesses wb->blkcg_css again via blkcg_unpin_online(). If css_put() drops the last reference, the blkcg can be freed asynchronously (css_free_rwork_fn -> blkcg_css_free -> kfree) before blkcg_unpin_online() dereferences the pointer to access blkcg->online_pin, resulting in a use-after-free: BUG: KASAN: slab-use-after-free in blkcg_unpin_online (./include/linux/instrumented.h:112 ./include/linux/atomic/atomic-instrumented.h:400 ./include/linux/refcount.h:389 ./include/linux/refcount.h:432 ./include/linux/refcount.h:450 block/blk-cgroup.c:1367) Write of size 4 at addr ff11000117aa6160 by task kworker/71:1/531 Workqueue: cgwb_release cgwb_release_workfn Call Trace: blkcg_unpin_online (./include/linux/instrumented.h:112 ./include/linux/atomic/atomic-instrumented.h:400 ./include/linux/refcount.h:389 ./include/linux/refcount.h:432 ./include/linux/refcount.h:450 block/blk-cgroup.c:1367) cgwb_release_workfn (mm/backing-dev.c:629) process_scheduled_works (kernel/workqueue.c:3278 kernel/workqueue.c:3385) Freed by task 1016: kfree (./include/linux/kasan.h:235 mm/slub.c:2689 mm/slub.c:6246 mm/slub.c:6561) css_free_rwork_fn (kernel/cgroup/cgroup.c:5542) process_scheduled_works (kernel/workqueue.c:3302 kernel/workqueue.c:3385) ** Stack based on commit 66672af7a095 ("Add linux-next specific files for 20260410") I am seeing this crash sporadically in Meta fleet across multiple kernel versions. A full reproducer is available at: https://github.com/leitao/debug/blob/main/reproducers/repro_blkcg_uaf.sh (The race window is narrow. To make it easily reproducible, inject a msleep(100) between css_put() and blkcg_unpin_online() in cgwb_release_workfn(). With that delay and a KASAN-enabled kernel, the reproducer triggers the splat reliably in less than a second.) Fix this by moving blkcg_unpin_online() before css_put(), so the cgwb's CSS reference keeps the blkcg alive while blkcg_unpin_online() accesses it. Link: https://lore.kernel.org/20260413-blkcg-v1-1-35b72622d16c@debian.org Fixes: 59b57717fff8 ("blkcg: delay blkg destruction until after writeback has finished") Signed-off-by: Breno Leitao Reviewed-by: Dennis Zhou Reviewed-by: Shakeel Butt Cc: David Hildenbrand Cc: Jens Axboe Cc: Johannes Weiner Cc: Josef Bacik Cc: JP Kobryn Cc: Liam Howlett Cc: Lorenzo Stoakes (Oracle) Cc: Martin KaFai Lau Cc: Michal Hocko Cc: Mike Rapoport Cc: Suren Baghdasaryan Cc: Tejun Heo Cc: Signed-off-by: Andrew Morton Signed-off-by: Greg Kroah-Hartman --- mm/backing-dev.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) --- a/mm/backing-dev.c +++ b/mm/backing-dev.c @@ -618,12 +618,13 @@ static void cgwb_release_workfn(struct w 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 */ blkcg_unpin_online(wb->blkcg_css); + css_put(wb->blkcg_css); + mutex_unlock(&wb->bdi->cgwb_release_mutex); + fprop_local_destroy_percpu(&wb->memcg_completions); spin_lock_irq(&cgwb_lock);