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 299FD381E94; Sun, 2 Aug 2026 11:25:50 +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=1785669952; cv=none; b=fYdhUO71WTSp3R5BAAiAdvYoNvxjx6Q0zDeVIlYSwywlHelBleA0IBgtKR/Vz2Xs702WHIuSirM1hLvZ53tlWl3mcauHU1pDLq2SS+og9TLC67RCJsJxDbIOVoMA5FVJxFppVnfLkwFMZxh20Ung2WxsyU4q+0aSHet/C8Q4v20= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785669952; c=relaxed/simple; bh=CbIcUGaG40OgJzRfbvqKSYTHTJMk+WRH2xbtk4uUbps=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=rX8YIrZoACsQpY3MM5CnRXx0WcuRlQC/2c/BhH9R4xndGjrCN7NFcdy3fS4yUJ7l1+jZCFG+l4IBsDT/jW0AG99xoq5rn1oDmDEolUDolo0VyYAfcpG0OtCZlp/cVMJ4qiPFy7wELtzYp/bkDzj4mjXiA8i5BisaI62N3YrBWnY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=C1u15YaA; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="C1u15YaA" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 30F731F000E9; Sun, 2 Aug 2026 11:25:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1785669950; bh=zU+TRKoCIS8QnsUNPujkhjRjzhengrzuAzjCZsXnVwM=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=C1u15YaALUspMGEXBQUaDY3xQPADr/4inUFUJzqWP7Pe7OdwtmjG19Ki0RdSOsj2/ LKkdvlt3eeNdKc4ciloR46liyglNsn4mIPOVnUWJL1+1R2ftBB9yRtrmFEFOWTzWPW OOml2u6cRIYpCIfp0jJKW+1FJOMFmaECDFK5JsaWzCI/D7+KT9jckn1xOjAcxnR34Q rILNF0mbNgXkUJKXgcOqnsx0mMijmhfnqCnZZai4M2Kggn/n8Ld5u92jVSQJ1mUAyL sQyr3iHif6M3ZoN7v+synZteN9TtAw2yPmUfdRUim3Cv6T07zbjwv2+mCcp1mloAPX s59/eYjTd+bCg== From: Yu Kuai To: tj@kernel.org, axboe@kernel.dk Cc: cgroups@vger.kernel.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, zhengqixing@huawei.com, hch@lst.de, yizhou.tang@shopee.com, yukuai@fygo.io, nilay@linux.ibm.com Subject: [PATCH v4 3/4] blk-cgroup: skip dying blkg in blkcg_activate_policy() Date: Sun, 2 Aug 2026 19:25:19 +0800 Message-ID: <20260802112525.3933753-4-yukuai@kernel.org> X-Mailer: git-send-email 2.51.0 In-Reply-To: <20260802112525.3933753-1-yukuai@kernel.org> References: <20260802112525.3933753-1-yukuai@kernel.org> Precedence: bulk X-Mailing-List: linux-block@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Zheng Qixing When switching IO schedulers on a block device, blkcg_activate_policy() can race with concurrent blkcg deletion, leading to a use-after-free in rcu_accelerate_cbs. T1: T2: blkg_destroy kill(&blkg->refcnt) // blkg->refcnt=1->0 blkg_release // call_rcu(__blkg_release) ... blkg_free_workfn ->pd_free_fn(pd) elv_iosched_store elevator_switch ... iterate blkg list blkg_get(blkg) // blkg->refcnt=0->1 list_del_init(&blkg->q_node) blkg_put(pinned_blkg) // blkg->refcnt=1->0 blkg_release // call_rcu again rcu_accelerate_cbs // uaf Fix this by checking hlist_unhashed(&blkg->blkcg_node) before getting a reference to the blkg. This is the same check used in blkg_destroy() to detect if a blkg has already been destroyed. If the blkg is already unhashed, skip processing it since it's being destroyed. Fixes: f1c006f1c685 ("blk-cgroup: synchronize pd_free_fn() from blkg_free_workfn() and blkcg_deactivate_policy()") Signed-off-by: Zheng Qixing Reviewed-by: Tang Yizhou Signed-off-by: Yu Kuai --- block/blk-cgroup.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c index 047bb42c282b..d1895bc60fcf 100644 --- a/block/blk-cgroup.c +++ b/block/blk-cgroup.c @@ -1577,6 +1577,8 @@ int blkcg_activate_policy(struct gendisk *disk, const struct blkcg_policy *pol) if (blkg->pd[pol->plid]) continue; + if (hlist_unhashed(&blkg->blkcg_node)) + continue; /* If prealloc matches, use it; otherwise try GFP_NOWAIT */ if (blkg == pinned_blkg) { -- 2.51.0