[alsa-devel] [PATCH] ALSA: compress: add support for 32bit calls in a 64bit kernel

[Takashi Iwai]

On Thu, 03 Dec 2015 06:32:09 +0100,
Ravindra Lokhande wrote:
> 
> Compress offload does not support ioctl calls from a 32bit userspace
> in a 64 bit kernel. This patch adds support for ioctls from a 32bit
> userspace in a 64bit kernel
> 
> Signed-off-by: Ravindra Lokhande <rlokhande at nvidia.com>
> ---
>  sound/core/compress_offload.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/sound/core/compress_offload.c b/sound/core/compress_offload.c
> index b123c42..98f6b47 100644
> --- a/sound/core/compress_offload.c
> +++ b/sound/core/compress_offload.c
> @@ -847,6 +847,15 @@ static long snd_compr_ioctl(struct file *f, unsigned int cmd, unsigned long arg)
>  	return retval;
>  }
>  
> +/* support of 32bit userspace on 64bit platforms */
> +#ifdef CONFIG_COMPAT
> +static long snd_compr_ioctl_compat(struct file *file, unsigned int cmd,
> +						unsigned long arg)
> +{
> +	return snd_compr_ioctl(file, cmd, arg);
> +}
> +#endif

This should work in most cases, but not perfectly.  The arg passed
here is basically a 32bit address, and it should be converted to a
64bit pointer via compat_ptr() macro.  Except for a very few
architectures, it's just a cast to 64bit, so it works in 99% cases.

A workaround would be like:

static long snd_compr_ioctl_compat(struct file *file, unsigned int cmd,
				   unsigned long arg)
{
	return snd_compr_ioctl(file, cmd, (long)compat_ptr(arg));
}


I looked through the current tree and found even a few places in
sound/core/* doing similarly wrong.  They need fixes...


thanks,

Takashi

> +
>  static const struct file_operations snd_compr_file_ops = {
>  		.owner =	THIS_MODULE,
>  		.open =		snd_compr_open,
> @@ -854,6 +863,9 @@ static const struct file_operations snd_compr_file_ops = {
>  		.write =	snd_compr_write,
>  		.read =		snd_compr_read,
>  		.unlocked_ioctl = snd_compr_ioctl,
> +#ifdef CONFIG_COMPAT
> +		.compat_ioctl = snd_compr_ioctl_compat,
> +#endif
>  		.mmap =		snd_compr_mmap,
>  		.poll =		snd_compr_poll,
>  };
> -- 
> 2.1.4
> 
>