From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 736BDF34C78 for ; Mon, 13 Apr 2026 17:44:51 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id CC7176B0088; Mon, 13 Apr 2026 13:44:50 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id C77D16B008A; Mon, 13 Apr 2026 13:44:50 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id BB59D6B0092; Mon, 13 Apr 2026 13:44:50 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id AF4276B0088 for ; Mon, 13 Apr 2026 13:44:50 -0400 (EDT) Received: from smtpin06.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay10.hostedemail.com (Postfix) with ESMTP id 7F706C144B for ; Mon, 13 Apr 2026 17:44:50 +0000 (UTC) X-FDA: 84654257940.06.713FA0D Received: from out-186.mta1.migadu.com (out-186.mta1.migadu.com [95.215.58.186]) by imf04.hostedemail.com (Postfix) with ESMTP id 868C440003 for ; Mon, 13 Apr 2026 17:44:48 +0000 (UTC) Authentication-Results: imf04.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=kF82xfwR; dmarc=pass (policy=none) header.from=linux.dev; spf=pass (imf04.hostedemail.com: domain of shakeel.butt@linux.dev designates 95.215.58.186 as permitted sender) smtp.mailfrom=shakeel.butt@linux.dev ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1776102288; a=rsa-sha256; cv=none; b=RXy09BfoQv3k8UEcUfCJPqmmH7Ejd4PtylGIjKlAQy3o+IvUKvGG++dLN+Fud0WZZlHWnY cOqwBdWt0io8pqJx54jwE5I9+CsVrlLg3l2sfowTbLp8mK+iQpsA/7Gz0e8TBHZIhDYncI tEcf859J0WJrBUXB4VTAVBv2V9LZWCo= ARC-Authentication-Results: i=1; imf04.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=kF82xfwR; dmarc=pass (policy=none) header.from=linux.dev; spf=pass (imf04.hostedemail.com: domain of shakeel.butt@linux.dev designates 95.215.58.186 as permitted sender) smtp.mailfrom=shakeel.butt@linux.dev ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1776102288; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=b0j9S/oeWv9cGrOnlEmdvesYiWMQozAk+6ZeIzA0Owc=; b=M5mzBi5oemFdTxeNysw4z3XAC/udaXLlKb0MpgtYw+sDmKMXw2nZoIMSNv7WZtg5W3UTaY BzKFXVCqoYh1KLN7WT6j05jtmEHC0R2RP6j18q7Kf5mNmj8calyIqm6JW2Nr1gI9X+1HG/ vcjT5LiIC4RF8eDFcgWx1bkFnv91brQ= Date: Mon, 13 Apr 2026 10:44:36 -0700 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1776102286; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=b0j9S/oeWv9cGrOnlEmdvesYiWMQozAk+6ZeIzA0Owc=; b=kF82xfwRKUDeEAuXqOchwk9JzjnHGoGfLr6ipXkTHA8Y9gDscmQu3i/dgmUx3cPA8uIVZb a4vMT/H+Owd+AsXn3B5FTclx+2LzDPYcGlTlnvfjefVUU4SzorZ631Fwoh1XzU06KX+uM+ TEyj96yOsj7dLckLcRg5oq87cs83K3A= X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Shakeel Butt To: Breno Leitao Cc: Andrew Morton , David Hildenbrand , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Tejun Heo , Jens Axboe , inwardvessel@gmail.com, hannes@cmpxchg.org, josef@toxicpanda.com, "Dennis Zhou (Facebook)" , linux-mm@kvack.org, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, martin.lau@linux.dev, usama.arif@linux.dev, kernel-team@meta.com, stable@vger.kernel.org Subject: Re: [PATCH] mm: blk-cgroup: fix use-after-free in cgwb_release_workfn() Message-ID: References: <20260413-blkcg-v1-1-35b72622d16c@debian.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260413-blkcg-v1-1-35b72622d16c@debian.org> X-Migadu-Flow: FLOW_OUT X-Rspamd-Queue-Id: 868C440003 X-Stat-Signature: p5sfhtwmzz15wcm9ojrk96nmdsbehsui X-Rspam-User: X-Rspamd-Server: rspam04 X-HE-Tag: 1776102288-513036 X-HE-Meta: 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 lIOZLLVS vIpA1QzVAiuHKjD7nheDuOlaLt0HSizQXUUB/xZaVByi1YhkLt36iLm485Qr5Q+pL6lL+M4jbWnoZFIX11s04jDy9htmg2jugp7kanDZQ/1k7odhwywvgVfVOMEOQlaC12Nnht1bRVqACti1UfO73da4kokycJ5H71Aa8hBJeRyJMej/2lkplyE4lkbnKmJDsSy4H2C//jceuEBzb6lKbimYkqpYYghdJuN/MwMayClluUwFdNpr92yLnKLSDiKaictlUG+4vmKYTxhYvKRO42hm78jD5E8BUnXUnl+vWP468Dfbiv4AX1h2N/TDsoCiwchR4Ppb3k726CyXxpExRvKiHAkPuG8fiWbBjMeZ8sR38Ans= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Apr 13, 2026 at 03:09:19AM -0700, Breno Leitao wrote: > 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. > > Fixes: 59b57717fff8 ("blkcg: delay blkg destruction until after writeback has finished") > Cc: stable@vger.kernel.org > Signed-off-by: Breno Leitao Reviewed-by: Shakeel Butt