linux-kernel - Re: [PATCH] dmabuf: use spinlock to access dmabuf->name

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Message-ID: <dcf2bdd6-d6fd-96f0-c6e7-6788ea282e35@codeaurora.org>
Date:   Wed, 17 Jun 2020 19:13:12 +0530
From:   Charan Teja Kalla <charante@...eaurora.org>
To:     David Laight <David.Laight@...LAB.COM>,
        "Ruhl, Michael J" <michael.j.ruhl@...el.com>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        "open list:DMA BUFFER SHARING FRAMEWORK" 
        <linux-media@...r.kernel.org>,
        DRI mailing list <dri-devel@...ts.freedesktop.org>
Cc:     Linaro MM SIG <linaro-mm-sig@...ts.linaro.org>,
        "vinmenon@...eaurora.org" <vinmenon@...eaurora.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: Re: [PATCH] dmabuf: use spinlock to access dmabuf->name



On 6/17/2020 1:51 PM, David Laight wrote:
> From: Charan Teja Kalla
>> Sent: 17 June 2020 07:29
> ...
>>>> If name is freed you will copy garbage, but the only way
>>>> for that to happen is that _set_name or _release have to be called
>>>> at just the right time.
>>>>
>>>> And the above would probably only be an issue if the set_name
>>>> was called, so you will get NULL or a real name.
>>
>> And there exists a use-after-free to avoid which requires the lock. Say
>> that memcpy() in dmabuffs_dname is in progress and in parallel _set_name
>> will free the same buffer that memcpy is operating on.
> 
> If the name is being looked at while the item is being freed
> you almost certainly have much bigger problems that just
> the name being a 'junk' pointer.

True, thus needs the lock.

> 
> 	David.
> 
> -
> Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
> Registration No: 1397386 (Wales)
> 

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