From nobody Mon Sep 29 21:07:50 2025 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 CCDFBC00140 for ; Tue, 16 Aug 2022 00:43:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1346649AbiHPAnj (ORCPT ); Mon, 15 Aug 2022 20:43:39 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49632 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1349560AbiHPAl3 (ORCPT ); Mon, 15 Aug 2022 20:41:29 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 68C2F18F5AE; Mon, 15 Aug 2022 13:39:31 -0700 (PDT) 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 0450E61227; Mon, 15 Aug 2022 20:39:31 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id F15E9C433C1; Mon, 15 Aug 2022 20:39:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1660595970; bh=bxzAdKnJvUOOeM9WOk9XQ+s41VBHpBHU+aYiSzddZcE=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=lc+LN1cEGpTRLc+RSPPT3UydCIE2FafxR9qBzqisR6u1M31MEx4jPxZdhuztasYRk iVfEG2kOA2UfsgxG+6hKADiRZwAxSujTrMkqCPS8MbsHmtG9Rzwu0bBETIGP/jJS/z LLzbmBXsFr+f35mSQKnHoxMZQcqGZ0eIn4yW1RmU= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Daniel Starke , Sasha Levin Subject: [PATCH 5.19 0931/1157] tty: n_gsm: fix race condition in gsmld_write() Date: Mon, 15 Aug 2022 20:04:47 +0200 Message-Id: <20220815180516.731737390@linuxfoundation.org> X-Mailer: git-send-email 2.37.2 In-Reply-To: <20220815180439.416659447@linuxfoundation.org> References: <20220815180439.416659447@linuxfoundation.org> User-Agent: quilt/0.67 MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" From: Daniel Starke [ Upstream commit 32dd59f96924f45e33bc79854f7a00679c0fa28e ] The function may be used by the user directly and also by the n_gsm internal functions. They can lead into a race condition which results in interleaved frames if both are writing at the same time. The receiving side is not able to decode those interleaved frames correctly. Add a lock around the low side tty write to avoid race conditions and frame interleaving between user originated writes and n_gsm writes. Fixes: e1eaea46bb40 ("tty: n_gsm line discipline") Signed-off-by: Daniel Starke Link: https://lore.kernel.org/r/20220701061652.39604-9-daniel.starke@siemen= s.com Signed-off-by: Greg Kroah-Hartman Signed-off-by: Sasha Levin --- drivers/tty/n_gsm.c | 21 +++++++++++++++++---- 1 file changed, 17 insertions(+), 4 deletions(-) diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c index 39359274096d..9a3d7db33394 100644 --- a/drivers/tty/n_gsm.c +++ b/drivers/tty/n_gsm.c @@ -2859,11 +2859,24 @@ static ssize_t gsmld_read(struct tty_struct *tty, s= truct file *file, static ssize_t gsmld_write(struct tty_struct *tty, struct file *file, const unsigned char *buf, size_t nr) { - int space =3D tty_write_room(tty); + struct gsm_mux *gsm =3D tty->disc_data; + unsigned long flags; + int space; + int ret; + + if (!gsm) + return -ENODEV; + + ret =3D -ENOBUFS; + spin_lock_irqsave(&gsm->tx_lock, flags); + space =3D tty_write_room(tty); if (space >=3D nr) - return tty->ops->write(tty, buf, nr); - set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags); - return -ENOBUFS; + ret =3D tty->ops->write(tty, buf, nr); + else + set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags); + spin_unlock_irqrestore(&gsm->tx_lock, flags); + + return ret; } =20 /** --=20 2.35.1