Return-Path: Date: Fri, 9 Mar 2012 16:08:39 +0100 From: Johan Hovold To: David Herrmann Cc: Marcel Holtmann , "Gustavo F. Padovan" , "David S. Miller" , linux-bluetooth@vger.kernel.org, linux-kernel@vger.kernel.org, netdev@vger.kernel.org, stable Subject: Re: [PATCH 1/2] bluetooth: hci_ldisc: fix NULL-pointer dereference on tty_close Message-ID: <20120309150839.GG4497@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> <20120309144013.GE4497@localhost> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 In-Reply-To: List-ID: On Fri, Mar 09, 2012 at 04:02:21PM +0100, David Herrmann wrote: > 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 wrote: > >> > On Thu, Mar 08, 2012 at 09:45:22AM -0800, Marcel Holtmann wrote: > >> >> > > > Do not close protocol driver until device has been unregistered. > >> >> > > > > >> >> > > > 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, but 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: uart-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 (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) > >> > ? ? ? ? ? ? ? ?return; > >> > > >> > ? ? ? ?BT_DBG("%s", hdev->name); > >> > - ? ? ? kfree(hdev->driver_data); > >> > ?} > >> > > >> > ?/* ------ LDISC part ------ */ > >> > @@ -316,6 +315,7 @@ static void hci_uart_tty_close(struct tty_struct *tty) > >> > ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?hci_free_dev(hdev); > >> > ? ? ? ? ? ? ? ? ? ? ? ?} > >> > ? ? ? ? ? ? ? ?} > >> > + ? ? ? ? ? ? ? kfree(hu); > >> > ? ? ? ?} > >> > ?} > >> > >> 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. > > > > 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. Agreed. > Or simply link to the patches that remove the destruct callback in the > -next tree. Yes, I would definitely mention those patches. > >> 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 { > >> + ? 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. > > Oops, I obviously meant hci_uart_tty_close(), sorry. Ouch. I should have realised it was a typo, sorry. Thanks, Johan