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, 09 Jun 2014 09:24:53 +0200
From:	Takashi Iwai <tiwai@...e.de>
To:	"Wang, Xiaoming" <xiaoming.wang@...el.com>
Cc:	vinod.koul@...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)

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.


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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