From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 DFB7132BF24; Sat, 30 May 2026 16:45:06 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780159508; cv=none; b=AL2QgmHOLuu6/8cTX6KA4+DdhAQj+yzdoXFci23Bqqp3WE6ZknO/MYXwkDj+j3S3p5993ajrBqtsatcR6lp9ZXP1hn3jOcIu7npAW7EsnOZfFlk5stfP+3aqL50Y7ztwuKCDoO/i05gMFk+qWZeKK6Pzc7IizXIcd51ud9QFR+s= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780159508; c=relaxed/simple; bh=eCdyhFr12Hm0koHID1vjgSy7mesOwAHeTrbz8LoyNCY=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=tK1RtNvDEeZYwzUqy2XZXWP4OQdyNli1Vzygt1BSL+yY1SI5GupFFKegHWC4DvHGaGEsKdCa34qq9UTOiJnwVKYtx42F3uYvWp13hLmYoL7BOCy/bc4lOHLJ6MGG150CJhWHVNclpyOH86SmggaGhoHuIqXQgKsiA52asx3W/nk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=VcS4h/Ol; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="VcS4h/Ol" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 23EAF1F00893; Sat, 30 May 2026 16:45:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1780159506; bh=Zfqqa6s4zxWPFJSq2FoWle3agMyugx2A3XMKqKjVAkg=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=VcS4h/Ol6y2CWzAwAaQz+zE0YD/4dJmLx7Z7Vtm/vmLe4gwLHcibFD/XgEjxFUvKi 4KRhzZhKY8qU3l1v7IpP/8IGxYNvnvaWGfWKpIMcFCTxQTCYnP3+Na3hDVt4HixH+6 419yXsnRjrJa4k+4pxkt/P8gywjL5x1g6+f2Xe9w= 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 6.1 100/969] mm: blk-cgroup: fix use-after-free in cgwb_release_workfn() Date: Sat, 30 May 2026 17:53:44 +0200 Message-ID: <20260530160303.089169315@linuxfoundation.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260530160300.485627683@linuxfoundation.org> References: <20260530160300.485627683@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 6.1-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 @@ -399,12 +399,13 @@ 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);