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

[Wang, Xiaoming]

Dear Takashi

> -----Original Message-----
> From: Koul, Vinod
> Sent: Monday, June 09, 2014 11:36 PM
> To: Takashi Iwai
> Cc: Wang, Xiaoming; Kp, Jeeja; dhowells@xxxxxxxxxx; arnd@xxxxxxxx;
> tglx@xxxxxxxxxxxxx; mtk.manpages@xxxxxxxxx;
> paulmck@xxxxxxxxxxxxxxxxxx; davej@xxxxxxxxxx;
> linux-kernel@xxxxxxxxxxxxxxx; Zhang, Dongxing
> 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@xxxxxxxxx>
> > > Signed-off-by: xiaoming wang <xiaoming.wang@xxxxxxxxx>
> >
> > 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!
Can you accept we add __attribute__((packed, aligned(4))) for struct snd_compr_avail
Which include the struct snd_compr_tstamp and fix the sizeof struct snd_compr_avail
to 0x1c both in 32bit and 64 bit kernel?
> 
> --
> ~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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