[alsa-devel] [PATCH] amixer: add support for TLV byte control read

[Vinod Koul]

On Fri, Jan 29, 2016 at 12:21:06PM +0530, Vinod Koul wrote:
> On Thu, Jan 28, 2016 at 05:19:21PM +0100, Takashi Iwai wrote:
> > The line number doesn't match with the latest code in git, so
> > double-check that the problem happens with the latest alsa-lib and
> > alsa-utils, too.
> 
> I am on debian packages 1.0.27
> 
> > I'm thinking whether this is rather an issue in the kernel driver
> > side.  In skl_tplg_tlv_control_get(),
> 
> I think you are right, the buffer would overflow which would cause heap to
> go bad and free goes crashing
> 
> > 
> > 	if (bc->params) {
> > 		if (copy_to_user(data, &bc->param_id, sizeof(u32)))
> > 			return -EFAULT;
> > 		if (copy_to_user(data + 1, &size, sizeof(u32)))
> > 			return -EFAULT;
> > 		if (copy_to_user(data + 2, bc->params, size))
> > 			return -EFAULT;
> > 	}
> > 
> > But here, size is the size of the whole container, not the size in the
> > container.  In the code above, you're copying size+8 bytes total and
> > this breaks the boundary already.
> 
> Right, also I think we need to check for size vs size of parameters. We
> don't want to copy kernel memory to usermode if usermode gave a larger
> buffer
> 
> Let me test this, thanks for pointing

And you were right :)

with this change it works and dumps 4K bytes on my screen

@@ -913,6 +913,13 @@ static int skl_tplg_tlv_control_get(struct snd_kcontrol
*kcontrol,
                skl_get_module_params(skl->skl_sst, (u32 *)bc->params,
                                      bc->max, bc->param_id, mconfig);

+       /* decrement size for TLV header */
+       size -= 2 * sizeof(u32);
+
+       /* check size as we don't want to send kernel data */
+       if (size > bc->max)
+               size = bc->max;
+
        if (bc->params) {
                if (copy_to_user(data, &bc->param_id, sizeof(u32)))
                        return -EFAULT;

Thanks
-- 
~Vinod