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

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Date:	Thu, 17 Sep 2015 12:28:11 +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

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
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-- 
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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