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 X-Spam-Level: X-Spam-Status: No, score=-6.5 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id A0FCDC28CBC for ; Wed, 6 May 2020 09:51:17 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [203.11.71.2]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 1AE552070B for ; Wed, 6 May 2020 09:51:17 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="pwtFY++f" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 1AE552070B Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linuxfoundation.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Received: from bilbo.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 49HBgL0GjnzDqbk for ; Wed, 6 May 2020 19:51:10 +1000 (AEST) Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=linuxfoundation.org (client-ip=198.145.29.99; helo=mail.kernel.org; envelope-from=gregkh@linuxfoundation.org; receiver=) Authentication-Results: lists.ozlabs.org; dmarc=none (p=none dis=none) header.from=linuxfoundation.org Authentication-Results: lists.ozlabs.org; dkim=pass (1024-bit key; unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=default header.b=pwtFY++f; dkim-atps=neutral Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 49HBcn3pkrzDqcK for ; Wed, 6 May 2020 19:48:57 +1000 (AEST) Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 7934F206DD; Wed, 6 May 2020 09:48:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588758533; bh=ZW1E79xPaZKAydY429DVMLY0e+c/wC5VYXN8YIirzjM=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=pwtFY++fxs2YNcNbbN+ZfgD+/9YnoIpehM4RYf+bS6ZuKVQf6QPag8gWpA0OrecEp G2ZCTCXXR3/YDgChIyUNUbIvPOKmS0Lf6irGRLNNWe1EfCOEz7QJ2p038mRUue0uSK cjs/cy+YpVrIdfXvi40mz6x60zA0GR0vRbom8Bb4= Date: Wed, 6 May 2020 11:48:51 +0200 From: Greg KH To: Raghavendra Rao Ananta Subject: Re: [PATCH] tty: hvc: Fix data abort due to race in hvc_open Message-ID: <20200506094851.GA2787548@kroah.com> References: <20200428032601.22127-1-rananta@codeaurora.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200428032601.22127-1-rananta@codeaurora.org> X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: andrew@daynix.com, linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org, jslaby@suse.com Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Mon, Apr 27, 2020 at 08:26:01PM -0700, Raghavendra Rao Ananta wrote: > Potentially, hvc_open() can be called in parallel when two tasks calls > open() on /dev/hvcX. In such a scenario, if the hp->ops->notifier_add() > callback in the function fails, where it sets the tty->driver_data to > NULL, the parallel hvc_open() can see this NULL and cause a memory abort. > Hence, serialize hvc_open and check if tty->private_data is NULL before > proceeding ahead. > > The issue can be easily reproduced by launching two tasks simultaneously > that does nothing but open() and close() on /dev/hvcX. > For example: > $ ./simple_open_close /dev/hvc0 & ./simple_open_close /dev/hvc0 & > > Signed-off-by: Raghavendra Rao Ananta > --- > drivers/tty/hvc/hvc_console.c | 16 ++++++++++++++-- > 1 file changed, 14 insertions(+), 2 deletions(-) > > diff --git a/drivers/tty/hvc/hvc_console.c b/drivers/tty/hvc/hvc_console.c > index 436cc51c92c3..ebe26fe5ac09 100644 > --- a/drivers/tty/hvc/hvc_console.c > +++ b/drivers/tty/hvc/hvc_console.c > @@ -75,6 +75,8 @@ static LIST_HEAD(hvc_structs); > */ > static DEFINE_MUTEX(hvc_structs_mutex); > > +/* Mutex to serialize hvc_open */ > +static DEFINE_MUTEX(hvc_open_mutex); > /* > * This value is used to assign a tty->index value to a hvc_struct based > * upon order of exposure via hvc_probe(), when we can not match it to > @@ -346,16 +348,24 @@ static int hvc_install(struct tty_driver *driver, struct tty_struct *tty) > */ > static int hvc_open(struct tty_struct *tty, struct file * filp) > { > - struct hvc_struct *hp = tty->driver_data; > + struct hvc_struct *hp; > unsigned long flags; > int rc = 0; > > + mutex_lock(&hvc_open_mutex); > + > + hp = tty->driver_data; > + if (!hp) { > + rc = -EIO; > + goto out; > + } > + > spin_lock_irqsave(&hp->port.lock, flags); > /* Check and then increment for fast path open. */ > if (hp->port.count++ > 0) { > spin_unlock_irqrestore(&hp->port.lock, flags); > hvc_kick(); > - return 0; > + goto out; > } /* else count == 0 */ > spin_unlock_irqrestore(&hp->port.lock, flags); Wait, why isn't this driver just calling tty_port_open() instead of trying to open-code all of this? Keeping a single mutext for open will not protect it from close, it will just slow things down a bit. There should already be a tty lock held by the tty core for open() to keep it from racing things, right? Try just removing all of this logic and replacing it with a call to tty_port_open() and see if that fixes this issue. As "proof" of this, I don't see other serial drivers needing a single mutex for their open calls, do you? thanks, greg k-h