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 3ED3A39150D; Wed, 24 Jun 2026 06:46:49 +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=1782283610; cv=none; b=QIcLyhbHMFDqFi8DwJcVmtrXFCbzUZumf9wjsXMgvJw8Ly/oYZoH+fItJGqWZn9iuGREO5UQrHh87apApr+63tE5surEVXfDf95Ag1qlKZ+o/Ms9syDkCNIRKqd705HgVa22Muq7/JsPBWa6wGnbUJx6ubzcW2pe0zeOhIe0jLY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782283610; c=relaxed/simple; bh=TuBq1EuVBCN2F3nRQtWtElfM/uUOviU5/aExIX4I9vQ=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=WqeFlBBGv6wVtQWQelGOaDElUBz9Vd09W+zEDLr6FbihUAgmnBqsGnILw+ASZV4Nl183wiF8kn0xasa44rRp0NB7jMuhPCcQXie2Co9KPTY9eAgXfWq5r6ZZvw3/Zk8gdgUvbKBEL7vgSbX6z33tyAVkWcfklb3je1TWYMpYmmw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=kKc/EQPr; 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="kKc/EQPr" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 054B71F000E9; Wed, 24 Jun 2026 06:46:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1782283609; bh=G4HfGCeNdq2zc5CMRZaEvNuo50V7VHV42j0cEQvxQTU=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=kKc/EQPrx8EiZiH0PGY7cTN1/iIB8v6PF1L5oT7EPGkOtjk2xIZDWRlu9PBoC0o/E S3+j6jaCfEi8aWqwf4ceQHdRHkCBZu/vHIl1AukIYR4JQzO6H4m0JkWfb8Z/Rri4Pz Fy2pFgz7zAohvSXI8ddU+pd8Q6FLdG3loXHQDdfBR6XuQuHZeTB2HTVZUPJTHHZnQx 4pMPVJ5a5cQO+e0mmuO76GyDkibb+EQVzsRYc99KQSm2B6759Qc6fP33A6WgO61Y5L WLcOJlhLH7dlO8sjhzb45l6HFN/vbIADGbAdyvoCG++DAYMDbH2BxL8F/zIp5QIBSi 7iCsNfdpn3ueQ== From: Yu Kuai To: Tejun Heo , Josef Bacik , Jens Axboe Cc: Zheng Qixing , Christoph Hellwig , Tang Yizhou , Nilay Shroff , Ming Lei , cgroups@vger.kernel.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH v2 3/4] blk-cgroup: skip dying blkg in blkcg_activate_policy() Date: Wed, 24 Jun 2026 14:46:24 +0800 Message-ID: <20260624064625.1743650-6-yukuai@kernel.org> X-Mailer: git-send-email 2.51.0 In-Reply-To: <20260624064625.1743650-1-yukuai@kernel.org> References: <20260624064625.1743650-1-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 f7e788a7fe95..2538d8105e6c 100644 --- a/block/blk-cgroup.c +++ b/block/blk-cgroup.c @@ -1574,10 +1574,12 @@ int blkcg_activate_policy(struct gendisk *disk, const struct blkcg_policy *pol) list_for_each_entry_reverse(blkg, &q->blkg_list, q_node) { struct blkg_policy_data *pd; 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) { pd = pd_prealloc; pd_prealloc = NULL; -- 2.51.0