linux-kernel - Re: [PATCH] ALSA: compress: Fix the mismatch size of struc between share lib(32bit) and kernel(64bit)

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Date:	Mon, 9 Jun 2014 21:05:44 +0530
From:	Vinod Koul <vinod.koul@...el.com>
To:	Takashi Iwai <tiwai@...e.de>
Cc:	"Wang, Xiaoming" <xiaoming.wang@...el.com>, jeeja.kp@...el.com,
	dhowells@...hat.com, arnd@...db.de, tglx@...utronix.de,
	mtk.manpages@...il.com, paulmck@...ux.vnet.ibm.com,
	davej@...hat.com, linux-kernel@...r.kernel.org,
	dongxing.zhang@...el.com
Subject: Re: [PATCH] ALSA: compress: Fix the mismatch size of struc between
 share lib(32bit) and kernel(64bit)

On Mon, Jun 09, 2014 at 09:24:53AM +0200, Takashi Iwai wrote:
> At Mon, 09 Jun 2014 16:46:32 -0400,
> Wang, Xiaoming wrote:
> > 
> > 
> > The size of struct snd_compr_avail is 0x1c in 32bit kernel,
> > while it is 0x20 in 64bit kernel 0x4 bytes added because of
> > alignment. It is OK when 32bit kernel met 32bit user space.
> > There exist stack corruption if 64bit kernel met 32bit user
> > space, because the size of struct snd_compr_avail is 0x1c
> > in 32bit user space which is smaller than it will get from
> > kernel. The extra 4 bytes can corrupt the stack, and
> > introduce unpredictable error.
> > 
> > Signed-off-by: Zhang Dongxing <dongxing.zhang@...el.com>
> > Signed-off-by: xiaoming wang <xiaoming.wang@...el.com>
> 
> This would break the existing 32bit systems, so I don't think we can
> take this approach.
> 
> Either break the 64bit systems (which aren't deployed yet much, so
> far) by adding packed attribute, or implement 32/64 bit conversion in
> compat_ioctl fop.
I think former should be safe for now. Anyway we have only 1 driver using this
in mainline so fallout shouldn't be widespread!

-- 
~Vinod
> 
> 
> thanks,
> 
> Takashi
> 
> > ---
> >  include/uapi/sound/compress_offload.h |    1 +
> >  1 files changed, 1 insertions(+), 0 deletions(-)
> > 
> > diff --git a/include/uapi/sound/compress_offload.h b/include/uapi/sound/compress_offload.h
> > index 5759810..766b416 100644
> > --- a/include/uapi/sound/compress_offload.h
> > +++ b/include/uapi/sound/compress_offload.h
> > @@ -70,6 +70,7 @@ struct snd_compr_tstamp {
> >  	__u32 pcm_frames;
> >  	__u32 pcm_io_frames;
> >  	__u32 sampling_rate;
> > +	__u32 reserved[1];
> >  };
> >  
> >  /**
> > -- 
> > 1.7.1
> > 

-- 
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