linux-kernel - Re: [PATCH] tty: fix data race in tty_buffer

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Date:	Thu, 17 Sep 2015 12:59:50 +0200
From:	Dmitry Vyukov <dvyukov@...gle.com>
To:	Peter Hurley <peter@...leysoftware.com>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jslaby@...e.com>,
	Linux kernel mailing list <linux-kernel@...r.kernel.org>,
	Jiri Slaby <jslaby@...e.cz>,
	Andrey Konovalov <andreyknvl@...gle.com>,
	Kostya Serebryany <kcc@...gle.com>,
	Alexander Potapenko <glider@...gle.com>,
	Paul McKenney <paulmck@...ux.vnet.ibm.com>,
	Hans Boehm <hboehm@...gle.com>
Subject: Re: [PATCH] tty: fix data race in tty_buffer_flush

I've resent the 3 patches with version information.

On Thu, Sep 17, 2015 at 12:28 PM, Dmitry Vyukov <dvyukov@...gle.com> wrote:
> One stupid question. There is a number of branches:
>   remotes/origin/master
>   remotes/origin/tty-linus
>   remotes/origin/tty-next
>   remotes/origin/tty-testing
>
> What branch should I base my patches on? I used master.
>
>
>
>
> On Wed, Sep 16, 2015 at 8:20 PM, Dmitry Vyukov <dvyukov@...gle.com> wrote:
>> Sorry for the delay. It is starred in my inbox and I plan to resend
>> the patches. Just did not have time yet.
>>
>>
>> On Wed, Sep 16, 2015 at 3:38 AM, Peter Hurley <peter@...leysoftware.com> wrote:
>>> On Tue, Sep 8, 2015 at 8:48 AM, Dmitry Vyukov <dvyukov@...gle.com> wrote:
>>>> tty_buffer_flush frees not acquired buffers.
>>>> As the result, for example, read of b->size in tty_buffer_free
>>>> can return garbage value which will lead to a huge buffer
>>>> hanging in the freelist. This is just the benignest
>>>> manifestation of freeing of a not acquired object.
>>>> If the object is passed to kfree, heap can be corrupted.
>>>>
>>>> Acquire visibility over the buffer before freeing it.
>>>>
>>>> The data race was found with KernelThreadSanitizer (KTSAN).
>>>
>>> Dmitry,
>>>
>>> Looks good. Thanks for splitting this from the other fix.
>>>
>>> Like Greg said, the patch needs revision info to help maintainers, et al
>>> track which is most current/relevant/etc.
>>>
>>> Typical format for $subject is something like:
>>>
>>> [PATCH v4] tty: fix data race in tty_buffer_flush
>>>
>>>
>>> Notes re: changes from other patch versions are added below the
>>> git changelog separator (example below).
>>>
>>>> Signed-off-by: Dmitry Vyukov <dvyukov@...gle.com>
>>>> ---
>>>
>>> v4: Corrected commit log and patch revision notes
>>>
>>> v3: Added code comment re: paired smp barrier
>>>
>>> v2: Split from 'tty: fix data races on tty_buffer.commit'
>>>
>>>>  drivers/tty/tty_buffer.c | 5 ++++-
>>>>  1 file changed, 4 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c
>>>> index 5a3fa89..a2a8cd0 100644
>>>> --- a/drivers/tty/tty_buffer.c
>>>> +++ b/drivers/tty/tty_buffer.c
>>>> @@ -242,7 +242,10 @@ void tty_buffer_flush(struct tty_struct *tty, struct tty_ldisc *ld)
>>>>         atomic_inc(&buf->priority);
>>>>
>>>>         mutex_lock(&buf->lock);
>>>> -       while ((next = buf->head->next) != NULL) {
>>>> +       /* paired w/ release in __tty_buffer_request_room; ensures there are
>>>> +        * no pending memory accesses to the freed buffer
>>>> +        */
>>>> +       while ((next = smp_load_acquire(&buf->head->next)) != NULL) {
>>>>                 tty_buffer_free(port, buf->head);
>>>>                 buf->head = next;
>>>>         }
>>>> --
>>>> 2.5.0.457.gab17608
>>>>
>>
>>
>>
>> --
>> Dmitry Vyukov, Software Engineer, dvyukov@...gle.com
>> Google Germany GmbH, Dienerstraße 12, 80331, München
>> Geschäftsführer: Graham Law, Christine Elizabeth Flores
>> Registergericht und -nummer: Hamburg, HRB 86891
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>> This e-mail is confidential. If you are not the right addressee please
>> do not forward it, please inform the sender, and please erase this
>> e-mail including any attachments. Thanks.
>
>
>
> --
> Dmitry Vyukov, Software Engineer, dvyukov@...gle.com
> Google Germany GmbH, Dienerstraße 12, 80331, München
> Geschäftsführer: Graham Law, Christine Elizabeth Flores
> Registergericht und -nummer: Hamburg, HRB 86891
> Sitz der Gesellschaft: Hamburg
> Diese E-Mail ist vertraulich. Wenn Sie nicht der richtige Adressat
> sind, leiten Sie diese bitte nicht weiter, informieren Sie den
> Absender und löschen Sie die E-Mail und alle Anhänge. Vielen Dank.
> This e-mail is confidential. If you are not the right addressee please
> do not forward it, please inform the sender, and please erase this
> e-mail including any attachments. Thanks.



-- 
Dmitry Vyukov, Software Engineer, dvyukov@...gle.com
Google Germany GmbH, Dienerstraße 12, 80331, München
Geschäftsführer: Graham Law, Christine Elizabeth Flores
Registergericht und -nummer: Hamburg, HRB 86891
Sitz der Gesellschaft: Hamburg
Diese E-Mail ist vertraulich. Wenn Sie nicht der richtige Adressat
sind, leiten Sie diese bitte nicht weiter, informieren Sie den
Absender und löschen Sie die E-Mail und alle Anhänge. Vielen Dank.
This e-mail is confidential. If you are not the right addressee please
do not forward it, please inform the sender, and please erase this
e-mail including any attachments. Thanks.
--
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