From mboxrd@z Thu Jan 1 00:00:00 1970 From: Johan Hovold Subject: Re: [PATCH 1/2] bluetooth: hci_ldisc: fix NULL-pointer dereference on tty_close Date: Fri, 9 Mar 2012 15:40:13 +0100 Message-ID: <20120309144013.GE4497@localhost> References: <1331136120-27075-1-git-send-email-jhovold@gmail.com> <1331136120-27075-2-git-send-email-jhovold@gmail.com> <1331148797.3392.191.camel@aeonflux> <20120308115721.GB4497@localhost> <1331228722.14217.7.camel@aeonflux> <20120309130413.GC4497@localhost> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: Marcel Holtmann , "Gustavo F. Padovan" , "David S. Miller" , linux-bluetooth@vger.kernel.org, linux-kernel@vger.kernel.org, netdev@vger.kernel.org, stable To: David Herrmann Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Fri, Mar 09, 2012 at 02:52:00PM +0100, David Herrmann wrote: > On Fri, Mar 9, 2012 at 2:04 PM, Johan Hovold wrot= e: > > On Thu, Mar 08, 2012 at 09:45:22AM -0800, Marcel Holtmann wrote: > >> > > > Do not close protocol driver until device has been unregiste= red. > >> > > > > >> > > > This fixes a race between tty_close and hci_dev_open which c= an result in > >> > > > a NULL-pointer dereference. > >> > > > > >> > > > The line discipline closes the protocol driver while we may = still have > >> > > > hci_dev_open sleeping on the req_lock mutex resulting in a N= ULL-pointer > >> > > > dereference when lock is acquired and hci_init_req called. > >> > > >> > [...] > >> > > >> > > what kernel version is this against? Our changes in bluetooth-= next fixed > >> > > some of the destruct handling. > >> > > >> > This is against the latest rc as it needs to be fixed in 3.3, bu= t I > >> > missed a dependency to bluetooth-next as you point out below. > >> > > >> > > Also hci_unregister_dev should be calling the destruct handler= and thus > >> > > your change is now accessing hu but it got freed already. > >> > > >> > You're right, my patch depends on 010666a126fc ("Bluetooth: Make > >> > hci-destruct callback optional") and 797fe796c4 ("Bluetooth: uar= t-ldisc: > >> > Fix memory leak and remove destruct cb") from bluetooth-next. > >> > > >> > But since the latter one fixes a memory leak it should have been= marked > >> > for stable as well as pushed to Linus for 3.3, right? > >> > >> we need to look into this and propose patches for -stable. Is your > >> problem still present with bluetooth-next or not? > > > > Yes, both races are present in bluetooth-next of today (b8622cbd58f= 34) > > and only takes an additional manual step to trigger (as the core no > > longer tries to open the device twice automatically). > > > > My two patches on top of either the two patches by David Herrmann > > mentioned above or the following minimal fix of the same memory lea= k > > would be sufficient to fix both races in 3.3: > > > > diff --git a/drivers/bluetooth/hci_ldisc.c b/drivers/bluetooth/hci_= ldisc.c > > index 0711448..97c5faa 100644 > > --- a/drivers/bluetooth/hci_ldisc.c > > +++ b/drivers/bluetooth/hci_ldisc.c > > @@ -237,7 +237,6 @@ static void hci_uart_destruct(struct hci_dev *h= dev) > > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0return; > > > > =A0 =A0 =A0 =A0BT_DBG("%s", hdev->name); > > - =A0 =A0 =A0 kfree(hdev->driver_data); > > =A0} > > > > =A0/* ------ LDISC part ------ */ > > @@ -316,6 +315,7 @@ static void hci_uart_tty_close(struct tty_struc= t *tty) > > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0hci_= free_dev(hdev); > > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0} > > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0} > > + =A0 =A0 =A0 =A0 =A0 =A0 =A0 kfree(hu); > > =A0 =A0 =A0 =A0} > > =A0} >=20 > The "destruct"-callback was broken in many ways but working around it > without removing it seems wrong. The reason for not doing so would be to keep the fixes minimal and thus more appropriate for the stable trees. =46urthermore, according to you patch own description "Several drivers already provide an empty callback" so I didn't consider it to be a problem. > This memory-leak occurs only if a > tty-device uses the uart-ldisc without a protocol bound to it. > Therefore, I didn't consider it important enough for stable. See my answer to you previous mail regarding this. > However, > if you want to fix this, leave the kfree() inside the destruct > callback but add another kfree() into the hci_uart_close() in an > "else"-clause like this: >=20 > if (test_and_clear_bit(...)) { > } else { > + kfree(...); > } You really don't want to free the hci_uart in it's own close method... The hci_uart is allocated in tty_open and should be freed in tty_close. > This will still keep the bogus ref-counts inside hci_dev with the > destruct() callback but will also free the ldisc if no protocol is > set. Thanks, Johan