From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Herrmann Subject: Re: [PATCH 1/2] bluetooth: hci_ldisc: fix NULL-pointer dereference on tty_close Date: Fri, 9 Mar 2012 16:02:21 +0100 Message-ID: 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> <20120309144013.GE4497@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: Johan Hovold Return-path: In-Reply-To: <20120309144013.GE4497@localhost> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Fri, Mar 9, 2012 at 3:40 PM, Johan Hovold wrote: > On Fri, Mar 09, 2012 at 02:52:00PM +0100, David Herrmann wrote: >> On Fri, Mar 9, 2012 at 2:04 PM, Johan Hovold wro= te: >> > On Thu, Mar 08, 2012 at 09:45:22AM -0800, Marcel Holtmann wrote: >> >> > > > Do not close protocol driver until device has been unregist= ered. >> >> > > > >> >> > > > This fixes a race between tty_close and hci_dev_open which = can 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 = NULL-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, b= ut I >> >> > missed a dependency to bluetooth-next as you point out below. >> >> > >> >> > > Also hci_unregister_dev should be calling the destruct handle= r and thus >> >> > > your change is now accessing hu but it got freed already. >> >> > >> >> > You're right, my patch depends on 010666a126fc ("Bluetooth: Mak= e >> >> > hci-destruct callback optional") and 797fe796c4 ("Bluetooth: ua= rt-ldisc: >> >> > Fix memory leak and remove destruct cb") from bluetooth-next. >> >> > >> >> > But since the latter one fixes a memory leak it should have bee= n 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 you= r >> >> problem still present with bluetooth-next or not? >> > >> > Yes, both races are present in bluetooth-next of today (b8622cbd58= f34) >> > and only takes an additional manual step to trigger (as the core n= o >> > 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 le= ak >> > 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_stru= ct *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} >> >> The "destruct"-callback was broken in many ways but working around i= t >> without removing it seems wrong. > > The reason for not doing so would be to keep the fixes minimal and th= us > more appropriate for the stable trees. > > Furthermore, according to you patch own description "Several drivers > already provide an empty callback" so I didn't consider it to be > a problem. It's just a proposal, feel free to keep your patch. But please include a comment in your commit-message that you explicitly avoid using the destruct-callback as it is, and always was, broken. Otherwise, it looks wrong seeing such a commit. Or simply link to the patches that remove the destruct callback in the -next tree. >> 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: >> >> if (test_and_clear_bit(...)) { >> } else { >> + =A0 kfree(...); >> } > > You really don't want to free the hci_uart in it's own close method..= =2E > > The hci_uart is allocated in tty_open and should be freed in tty_clos= e. Oops, I obviously meant hci_uart_tty_close(), sorry. >> 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