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 9C11033A712; Fri, 9 Jan 2026 11:54:18 +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=1767959658; cv=none; b=ILwlcOBKprcbhqHuZ/iFpK6CMWYNWxqvWhQFDdAQVJGOZQ/eIlA5yjmGj63cXN2DKL9x8200B0nWDvsdgEo3hBgMfgm9bUQgjfOB91rbq6FTjGc38v52o4D+mrLWSf3xXLIHQyftKrSdda6oxrqUqIAjGLqoxIwzgWkcLq0znI4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1767959658; c=relaxed/simple; bh=jEqTUOGX9CbuJ99nYKhoCX3r0e5MqBamLT+WN3Au1Ig=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=E8nA3SDTzCSBxa+m5aeY645oqD2NpEKMF4jvj9ZlczH/V5w3sfcSrFg1eLtbtbfLcAgOFlW2VfkQ8f0wI2Nw4mggEwoNjv2zNdSVaK1HnZRS6G6OkPyao2Cqa9jA7WSnNqFBkE/isWDeu1JkUvY9MhkmDwRmdRwS0BROq2x1/Ho= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=ZsvVZF9/; 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="ZsvVZF9/" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2C98CC4CEF1; Fri, 9 Jan 2026 11:54:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1767959658; bh=jEqTUOGX9CbuJ99nYKhoCX3r0e5MqBamLT+WN3Au1Ig=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=ZsvVZF9/qivAEPITCUx4wDPFYCX1H8Do6p393I+Kr5RuwkVTOsPwecZ19rygBgJdr fICuAWnW+4fGfFmb12m+SLMqy0YbGmBvLuiCkLm90N+L8Y64kEgSEx+Ro/8ARCjVMG ak1y66iDEa2C4LW6sq3wI/2kJY2pa/ZySdoiQs8I= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, syzbot+56fbf4c7ddf65e95c7cc@syzkaller.appspotmail.com, Zheng Qixing , Jens Axboe , Sasha Levin Subject: [PATCH 6.6 129/737] nbd: defer config put in recv_work Date: Fri, 9 Jan 2026 12:34:28 +0100 Message-ID: <20260109112138.855234162@linuxfoundation.org> X-Mailer: git-send-email 2.52.0 In-Reply-To: <20260109112133.973195406@linuxfoundation.org> References: <20260109112133.973195406@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.6-stable review patch. If anyone has any objections, please let me know. ------------------ From: Zheng Qixing [ Upstream commit 9517b82d8d422d426a988b213fdd45c6b417b86d ] There is one uaf issue in recv_work when running NBD_CLEAR_SOCK and NBD_CMD_RECONFIGURE: nbd_genl_connect // conf_ref=2 (connect and recv_work A) nbd_open // conf_ref=3 recv_work A done // conf_ref=2 NBD_CLEAR_SOCK // conf_ref=1 nbd_genl_reconfigure // conf_ref=2 (trigger recv_work B) close nbd // conf_ref=1 recv_work B config_put // conf_ref=0 atomic_dec(&config->recv_threads); -> UAF Or only running NBD_CLEAR_SOCK: nbd_genl_connect // conf_ref=2 nbd_open // conf_ref=3 NBD_CLEAR_SOCK // conf_ref=2 close nbd nbd_release config_put // conf_ref=1 recv_work config_put // conf_ref=0 atomic_dec(&config->recv_threads); -> UAF Commit 87aac3a80af5 ("nbd: call nbd_config_put() before notifying the waiter") moved nbd_config_put() to run before waking up the waiter in recv_work, in order to ensure that nbd_start_device_ioctl() would not be woken up while nbd->task_recv was still uncleared. However, in nbd_start_device_ioctl(), after being woken up it explicitly calls flush_workqueue() to make sure all current works are finished. Therefore, there is no need to move the config put ahead of the wakeup. Move nbd_config_put() to the end of recv_work, so that the reference is held for the whole lifetime of the worker thread. This makes sure the config cannot be freed while recv_work is still running, even if clear + reconfigure interleave. In addition, we don't need to worry about recv_work dropping the last nbd_put (which causes deadlock): path A (netlink with NBD_CFLAG_DESTROY_ON_DISCONNECT): connect // nbd_refs=1 (trigger recv_work) open nbd // nbd_refs=2 NBD_CLEAR_SOCK close nbd nbd_release nbd_disconnect_and_put flush_workqueue // recv_work done nbd_config_put nbd_put // nbd_refs=1 nbd_put // nbd_refs=0 queue_work path B (netlink without NBD_CFLAG_DESTROY_ON_DISCONNECT): connect // nbd_refs=2 (trigger recv_work) open nbd // nbd_refs=3 NBD_CLEAR_SOCK // conf_refs=2 close nbd nbd_release nbd_config_put // conf_refs=1 nbd_put // nbd_refs=2 recv_work done // conf_refs=0, nbd_refs=1 rmmod // nbd_refs=0 Reported-by: syzbot+56fbf4c7ddf65e95c7cc@syzkaller.appspotmail.com Closes: https://lore.kernel.org/all/6907edce.a70a0220.37351b.0014.GAE@google.com/T/ Fixes: 87aac3a80af5 ("nbd: make the config put is called before the notifying the waiter") Depends-on: e2daec488c57 ("nbd: Fix hungtask when nbd_config_put") Signed-off-by: Zheng Qixing Signed-off-by: Jens Axboe Signed-off-by: Sasha Levin --- drivers/block/nbd.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c index 27a05b1521f69..9e190d220e98f 100644 --- a/drivers/block/nbd.c +++ b/drivers/block/nbd.c @@ -912,9 +912,9 @@ static void recv_work(struct work_struct *work) nbd_mark_nsock_dead(nbd, nsock, 1); mutex_unlock(&nsock->tx_lock); - nbd_config_put(nbd); atomic_dec(&config->recv_threads); wake_up(&config->recv_wq); + nbd_config_put(nbd); kfree(args); } -- 2.51.0