Seg. fault when using Salsa 0.0.25

Seg. fault when using Salsa 0.0.25

[Mogens Lindholdt Lauridsen]

Hi,

I got an application which uses Salsa 0.0.25. When I quit this 
application, it ends with a seg. fault.

I don't know if this is caused by my application using Salsa wrongly, or a 
problem in Salsa.

However, I got a fix for it.

When my application closes, "hctl_elem_event_handler" is called. And since 
"helem->private_data" is null, this causes a seg. fault:
        snd_mixer_elem_t *elem = helem->private_data;
        snd_mixer_t *mixer = elem->mixer;

It seems like:
        if (!elem)
                return 0;
should have been before:
        snd_mixer_t *mixer = elem->mixer;

An easy way to fix/avoid this is to remove "snd_mixer_t *mixer = 
elem->mixer;" and replace "mixer" with "elem->mixer" in the function. Like 
this:

static int hctl_elem_event_handler(snd_hctl_elem_t *helem,
                                   unsigned int mask)
{
        snd_mixer_elem_t *elem = helem->private_data;
//MLN fix:      snd_mixer_t *mixer = elem->mixer;
        int err;

        if (!elem)
                return 0;

        if (mask == SND_CTL_EVENT_MASK_REMOVE) {
                err = _snd_mixer_elem_throw_event(elem, mask);
                if (err < 0)
                        return err;
                remove_simple_element(helem, 1);
                return 0;
        }
        if (mask & SND_CTL_EVENT_MASK_INFO) {
                remove_simple_element(helem, 0);
                add_simple_element(helem, elem->mixer); // MLN fix: 
"mixer" substituted by "elem->mixer"
                err = snd_mixer_elem_info(elem);
                if (err < 0)
                        return err;
                snd_mixer_sort(elem->mixer);  // MLN fix: "mixer" 
substituted by "elem->mixer"
        }
        if (mask & SND_CTL_EVENT_MASK_VALUE) {
                err = update_simple_element(helem, elem);
                if (err < 0)
                        return err;
                if (err) {
                        err = snd_mixer_elem_value(elem);
                        if (err < 0)
                                return err;
                }
        }
        return 0;
}

Kind regards,
Mogens

Re: Seg. fault when using Salsa 0.0.25

[Takashi Iwai]

At Thu, 5 Nov 2009 11:32:39 +0100,
Mogens Lindholdt Lauridsen wrote:
> 
> Hi,
> 
> I got an application which uses Salsa 0.0.25. When I quit this 
> application, it ends with a seg. fault.
> 
> I don't know if this is caused by my application using Salsa wrongly, or a 
> problem in Salsa.
> 
> However, I got a fix for it.
> 
> When my application closes, "hctl_elem_event_handler" is called. And since 
> "helem->private_data" is null, this causes a seg. fault:
>         snd_mixer_elem_t *elem = helem->private_data;
>         snd_mixer_t *mixer = elem->mixer;
> 
> It seems like:
>         if (!elem)
>                 return 0;
> should have been before:
>         snd_mixer_t *mixer = elem->mixer;

Ah, a typical NULL dereference.
Fixed and released as version 0.0.26 now.


thanks,

Takashi