linux-kernel - Re: [PATCH v2] vmw_balloon: fixing double free when batching mode is off

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Message-ID: <BB21DC03-9168-4E5E-B5CA-D446E07BE52F@vmware.com>
Date:   Mon, 19 Mar 2018 18:52:53 +0000
From:   Nadav Amit <namit@...are.com>
To:     Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Oleksandr Natalenko <onatalen@...hat.com>
CC:     Xavier Deguillard <xdeguillard@...are.com>,
        pv-drivers <pv-drivers@...are.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Gil Kupfer <gilkup@...il.com>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: Re: [PATCH v2] vmw_balloon: fixing double free when batching mode is
 off

Nadav Amit <namit@...are.com> wrote:

> Nadav Amit <namit@...are.com> wrote:
> 
>> From: Gil Kupfer <gilkup@...il.com>
>> 
>> The balloon.page field is used for two different purposes if batching is
>> on or off. If batching is on, the field point to the page which is used
>> to communicate with with the hypervisor. If it is off, balloon.page
>> points to the page that is about to be (un)locked.
>> 
>> Unfortunately, this dual-purpose of the field introduced a bug: when the
>> balloon is popped (e.g., when the machine is reset or the balloon driver
>> is explicitly removed), the balloon driver frees, unconditionally, the
>> page that is held in balloon.page.  As a result, if batching is
>> disabled, this leads to double freeing the last page that is sent to the
>> hypervisor.
> 
> Oleksandr, if you can confirm that it fixes the bug you encountered, it
> would be great.
> 
> Greg, Arnd, on your free time, please let me know if there is any issue
> with the patch, and whether you can incorporate it, preferably in 4.16,
> since it is a bug-fix that was encountered by Red-Hat customers.

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