linux-kernel - Re: [PATCH 4.4.y] ALSA: pcm: Add missing copy ops check before clearing buffer

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Date:   Wed, 29 Jan 2020 10:55:21 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Takashi Iwai <tiwai@...e.de>
Cc:     Andreas Schneider <asn@...ptomilk.org>, stable@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4.4.y] ALSA: pcm: Add missing copy ops check before
 clearing buffer

On Wed, Jan 29, 2020 at 10:40:41AM +0100, Takashi Iwai wrote:
> [ this is a fix specific to 4.4.y and 4.9.y stable trees;
>   4.14.y and older already contain the right fix ]
> 
> The stable 4.4.y and 4.9.y backports of the upstream commit
> add9d56d7b37 ("ALSA: pcm: Avoid possible info leaks from PCM stream
> buffers") dropped the check of substream->ops->copy_user as copy_user
> is a new member that isn't present in the older kernels.
> Although upstream drivers should work without this NULL check, it may
> cause a regression with a downstream driver that sets some
> inaccessible address to runtime->dma_area, leading to a crash at
> worst.
> 
> Since such drivers must have ops->copy member on older kernels instead
> of ops->copy_user, this patch adds the missing check of ops->copy for
> fixing the regression.
> 
> Reported-and-tested-by: Andreas Schneider <asn@...ptomilk.org>
> Signed-off-by: Takashi Iwai <tiwai@...e.de>

Thanks for the fix!

greg k-h