From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from lindbergh.monkeyblade.net (lindbergh.monkeyblade.net [23.128.96.19]) (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 B56CB644 for ; Sat, 27 May 2023 05:57:23 +0000 (UTC) Received: from metis.ext.pengutronix.de (metis.ext.pengutronix.de [IPv6:2001:67c:670:201:290:27ff:fe1d:cc33]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2D15C116 for ; Fri, 26 May 2023 22:57:22 -0700 (PDT) Received: from ptx.hi.pengutronix.de ([2001:67c:670:100:1d::c0]) by metis.ext.pengutronix.de with esmtps (TLS1.3:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1q2mvL-0005pl-A3; Sat, 27 May 2023 07:57:07 +0200 Received: from ore by ptx.hi.pengutronix.de with local (Exim 4.92) (envelope-from ) id 1q2mvI-0004cX-A8; Sat, 27 May 2023 07:57:04 +0200 Date: Sat, 27 May 2023 07:57:04 +0200 From: Oleksij Rempel To: Fedor Pchelkin Cc: Oleksij Rempel , Marc Kleine-Budde , kernel@pengutronix.de, Robin van der Gracht , Oliver Hartkopp , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Kurt Van Dijck , linux-can@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Alexey Khoroshilov , lvc-project@linuxtesting.org Subject: Re: [PATCH 2/2] can: j1939: avoid possible use-after-free when j1939_can_rx_register fails Message-ID: <20230527055704.GA17237@pengutronix.de> References: <20230526171910.227615-1-pchelkin@ispras.ru> <20230526171910.227615-3-pchelkin@ispras.ru> <20230526181500.GA26860@pengutronix.de> <20230526185026.33pcjvoyq5jzlnxk@fpc> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20230526185026.33pcjvoyq5jzlnxk@fpc> X-Sent-From: Pengutronix Hildesheim X-URL: http://www.pengutronix.de/ X-Accept-Language: de,en X-Accept-Content-Type: text/plain User-Agent: Mutt/1.10.1 (2018-07-13) X-SA-Exim-Connect-IP: 2001:67c:670:100:1d::c0 X-SA-Exim-Mail-From: ore@pengutronix.de X-SA-Exim-Scanned: No (on metis.ext.pengutronix.de); SAEximRunCond expanded to false X-PTX-Original-Recipient: netdev@vger.kernel.org X-Spam-Status: No, score=-4.2 required=5.0 tests=BAYES_00,RCVD_IN_DNSWL_MED, SPF_HELO_NONE,SPF_PASS,T_SCC_BODY_TEXT_LINE autolearn=unavailable autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Hi Fedor, On Fri, May 26, 2023 at 09:50:26PM +0300, Fedor Pchelkin wrote: > Hi Oleksij, > > thanks for the reply! > > On Fri, May 26, 2023 at 08:15:00PM +0200, Oleksij Rempel wrote: > > Hi Fedor, > > > > On Fri, May 26, 2023 at 08:19:10PM +0300, Fedor Pchelkin wrote: > > > > > > Thank you for your investigation. How about this change? > > --- a/net/can/j1939/main.c > > +++ b/net/can/j1939/main.c > > @@ -285,8 +285,7 @@ struct j1939_priv *j1939_netdev_start(struct net_device *ndev) > > */ > > kref_get(&priv_new->rx_kref); > > spin_unlock(&j1939_netdev_lock); > > - dev_put(ndev); > > - kfree(priv); > > + j1939_priv_put(priv); > > I don't think that's good because the priv which is directly freed here is > still local to the thread, and parallel threads don't have any access to > it. j1939_priv_create() has allocated a fresh priv and called dev_hold() > so dev_put() and kfree() here are okay. > > > return priv_new; > > } > > j1939_priv_set(ndev, priv); > > @@ -300,8 +299,7 @@ struct j1939_priv *j1939_netdev_start(struct net_device *ndev) > > > > out_priv_put: > > j1939_priv_set(ndev, NULL); > > - dev_put(ndev); > > - kfree(priv); > > + j1939_priv_put(priv); > > > > return ERR_PTR(ret); > > } > > > > If I see it correctly, the problem is kfree() which is called without respecting > > the ref counting. If CPU1 has priv_new, refcounting is increased. The priv will > > not be freed on this place. > > With your suggestion, I think it doesn't work correctly if > j1939_can_rx_register() fails and we go to out_priv_put. The priv is kept > but the parallel thread which may have already grabbed it thinks that > j1939_can_rx_register() has succeeded when actually it hasn't succeed. > Moreover, j1939_priv_set() makes it NULL on error path so that priv cannot > be accessed from ndev. > > I also considered the alternatives where we don't have to serialize access > to j1939_can_rx_register() and subsequently introduce mutex. But with > current j1939_netdev_start() implementation I can't see how to fix the > racy bug without it. Ok, it make sense. I'll try to do some testing next week. If i'll forget it, please feel free to ping me. Regards, Oleksij -- Pengutronix e.K. | | Steuerwalder Str. 21 | http://www.pengutronix.de/ | 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |