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 E216F2C08C8 for ; Mon, 20 Apr 2026 14:49:29 +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=1776696570; cv=none; b=Tx4e8O+GDdvFxTcJFgQ1YqOCSjFfRVbQ7z+FhA65iIOh07JMtV3/nzRvliXinz6eAoMZImWRdOX/UiEa+lo8xAFom0+E3IEnkfF05f1EfvkFk9hoFNlZxOMgGxRyma9q1KbYw3A+MYV9MakEqhtaCi8lqiEUOXG2Pq9ZiWSSyeM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776696570; c=relaxed/simple; bh=CQTM7/MVskmvprpIt1GSpKHltL5GDrc7bRQ7UCtUQgc=; h=Subject:To:Cc:From:Date:Message-ID:MIME-Version:Content-Type; b=jrdGX4Opg0wDa7HWN4dG84cBykj+ksIU+NkW3WFOUn0u9oAhTm2syfRJfcSgI31kvqcp29L97V7cs2rNsrI9gn5waV5PPzQxXrP6/EYnO+xuni1R5ju9lpzXrK9LuC/wuI19CqF4noxv/SsQmB4TrMQTDWUmO3Pb96Ti5vlK+So= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=LKB+XJhm; 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="LKB+XJhm" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3A898C19425; Mon, 20 Apr 2026 14:49:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1776696569; bh=CQTM7/MVskmvprpIt1GSpKHltL5GDrc7bRQ7UCtUQgc=; h=Subject:To:Cc:From:Date:From; b=LKB+XJhmqCPdqXyEnf3v0gAbA20TcE9m/+uMDPcseuf8MifbNFOOIuB4w8jYrhZt8 F2U5aWRQvniAKzSPYHUOiCogeJAEJx1dLU1M3r9Y22TbsMZW+LK+kPJrW6fBJKdSfC wk57aI2u9boM6+q03dGbwJdVT55nSxq1jDXYlJFk= Subject: FAILED: patch "[PATCH] mm: blk-cgroup: fix use-after-free in cgwb_release_workfn()" failed to apply to 5.15-stable tree To: leitao@debian.org,akpm@linux-foundation.org,axboe@kernel.dk,david@kernel.org,dennis@kernel.org,hannes@cmpxchg.org,inwardvessel@gmail.com,josef@toxicpanda.com,liam.howlett@oracle.com,ljs@kernel.org,martin.lau@linux.dev,mhocko@suse.com,rppt@kernel.org,shakeel.butt@linux.dev,stable@vger.kernel.org,surenb@google.com,tj@kernel.org Cc: From: Date: Mon, 20 Apr 2026 16:49:27 +0200 Message-ID: <2026042027-thinly-unrigged-91da@gregkh> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=ANSI_X3.4-1968 Content-Transfer-Encoding: 8bit The patch below does not apply to the 5.15-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to . To reproduce the conflict and resubmit, you may use the following commands: git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y git checkout FETCH_HEAD git cherry-pick -x 8f5857be99f1ed1fa80991c72449541f634626ee # git commit -s git send-email --to '' --in-reply-to '2026042027-thinly-unrigged-91da@gregkh' --subject-prefix 'PATCH 5.15.y' HEAD^.. Possible dependencies: thanks, greg k-h ------------------ original commit in Linus's tree ------------------ >From 8f5857be99f1ed1fa80991c72449541f634626ee Mon Sep 17 00:00:00 2001 From: Breno Leitao Date: Mon, 13 Apr 2026 03:09:19 -0700 Subject: [PATCH] mm: blk-cgroup: fix use-after-free in cgwb_release_workfn() 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 diff --git a/mm/backing-dev.c b/mm/backing-dev.c index 7a18fa6c7272..cecbcf9060a6 100644 --- a/mm/backing-dev.c +++ b/mm/backing-dev.c @@ -618,12 +618,13 @@ 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 */ 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);