Return-Path: MIME-Version: 1.0 In-Reply-To: <20120309130413.GC4497@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> Date: Fri, 9 Mar 2012 14:52:00 +0100 Message-ID: Subject: Re: [PATCH 1/2] bluetooth: hci_ldisc: fix NULL-pointer dereference on tty_close From: David Herrmann To: Johan Hovold Cc: Marcel Holtmann , "Gustavo F. Padovan" , "David S. Miller" , linux-bluetooth@vger.kernel.org, linux-kernel@vger.kernel.org, netdev@vger.kernel.org, stable Content-Type: text/plain; charset=ISO-8859-1 List-ID: On Fri, Mar 9, 2012 at 2:04 PM, Johan Hovold wrote: > On Thu, Mar 08, 2012 at 09:45:22AM -0800, Marcel Holtmann wrote: >> Hi Johan, >> >> > > > Do not close protocol driver until device has been unregistered. >> > > > >> > > > This fixes a race between tty_close and hci_dev_open which can res= ult 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 NULL-po= inter >> > > > dereference when lock is acquired and hci_init_req called. >> > >> > [...] >> > >> > > what kernel version is this against? Our changes in bluetooth-next f= ixed >> > > some of the destruct handling. >> > >> > This is against the latest rc as it needs to be fixed in 3.3, but I >> > missed a dependency to bluetooth-next as you point out below. >> > >> > > Also hci_unregister_dev should be calling the destruct handler and t= hus >> > > 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: uart-ldis= c: >> > Fix memory leak and remove destruct cb") from bluetooth-next. >> > >> > But since the latter one fixes a memory leak it should have been marke= d >> > 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 (b8622cbd58f34) > 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 leak > 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 *hdev) > =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_struct *tty= ) > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0hci_free_d= ev(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} The "destruct"-callback was broken in many ways but working around it without removing it seems wrong. 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. 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: if (test_and_clear_bit(...)) { } else { + kfree(...); } 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. Regards David > > Thanks, > Johan > -- > To unsubscribe from this list: send the line "unsubscribe linux-bluetooth= " in > the body of a message to majordomo@vger.kernel.org > More majordomo info at =A0http://vger.kernel.org/majordomo-info.html