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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id A83F3C433F5 for ; Mon, 28 Feb 2022 17:46:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238572AbiB1Rqn (ORCPT ); Mon, 28 Feb 2022 12:46:43 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33492 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239120AbiB1Rnp (ORCPT ); Mon, 28 Feb 2022 12:43:45 -0500 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1171C9BAF3; Mon, 28 Feb 2022 09:35:44 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 99619614CD; Mon, 28 Feb 2022 17:35:43 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id A5210C340E7; Mon, 28 Feb 2022 17:35:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1646069743; bh=W+oyjTCIxWodUCtLNaLKp1/WhBPmLkZ4yWLomJTkxbk=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=U1MoFrqmeI/sVDkE2Cl0IFXtRVc/xhO2+qzILeg4n6QTGuxNKlS8y7sKeLSe58QEN njAGe1Rv3UkrRhtnvAfxOeM8eSZOPFs9Umhtmu53pTY9XzwlAuTW2xlconsjBwBxFV yaAWrY7QRKCYVI9ONcsA6qTxJG5U4hvm4h3f4270= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Daniel Starke Subject: [PATCH 5.10 76/80] tty: n_gsm: fix NULL pointer access due to DLCI release Date: Mon, 28 Feb 2022 18:24:57 +0100 Message-Id: <20220228172320.940705546@linuxfoundation.org> X-Mailer: git-send-email 2.35.1 In-Reply-To: <20220228172311.789892158@linuxfoundation.org> References: <20220228172311.789892158@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: daniel.starke@siemens.com commit 96b169f05cdcc844b400695184d77e42071d14f2 upstream. The here fixed commit made the tty hangup asynchronous to avoid a circular locking warning. I could not reproduce this warning. Furthermore, due to the asynchronous hangup the function call now gets queued up while the underlying tty is being freed. Depending on the timing this results in a NULL pointer access in the global work queue scheduler. To be precise in process_one_work(). Therefore, the previous commit made the issue worse which it tried to fix. This patch fixes this by falling back to the old behavior which uses a blocking tty hangup call before freeing up the associated tty. Fixes: 7030082a7415 ("tty: n_gsm: avoid recursive locking with async port hangup") Cc: stable@vger.kernel.org Signed-off-by: Daniel Starke Link: https://lore.kernel.org/r/20220218073123.2121-4-daniel.starke@siemens.com Signed-off-by: Greg Kroah-Hartman --- drivers/tty/n_gsm.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) --- a/drivers/tty/n_gsm.c +++ b/drivers/tty/n_gsm.c @@ -1719,7 +1719,12 @@ static void gsm_dlci_release(struct gsm_ gsm_destroy_network(dlci); mutex_unlock(&dlci->mutex); - tty_hangup(tty); + /* We cannot use tty_hangup() because in tty_kref_put() the tty + * driver assumes that the hangup queue is free and reuses it to + * queue release_one_tty() -> NULL pointer panic in + * process_one_work(). + */ + tty_vhangup(tty); tty_port_tty_set(&dlci->port, NULL); tty_kref_put(tty);