SEGFault when optininal snd_ctl_ext_callback::read_event() not set
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Message ID B0FB33DC1499054591F62C0EF1E013D7684A3E29@HI2EXCH01.adit-jv.com
State New
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Commit Message

Timo Wischer Oct. 5, 2017, 2:28 p.m. UTC
Hi Takashi,

see attached the patch.
From my opinion failing with an error is the best solution (see explanation in the commit message)


Best regards

Timo Wischer

Advanced Driver Information Technology GmbH
Engineering Software Base (ADITG/ESB)
Robert-Bosch-Str. 200
31139 Hildesheim
Germany

Tel. +49 5121 49 6938
Fax +49 5121 49 6999
twischer@de.adit-jv.com

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Comments

Takashi Iwai Oct. 5, 2017, 2:44 p.m. UTC | #1
On Thu, 05 Oct 2017 16:28:33 +0200,
Wischer, Timo (ADITG/ESB) wrote:
> 
> Hi Takashi,
> 
> see attached the patch.
> >From my opinion failing with an error is the best solution (see explanation in the commit message)

Fair enough, applied now.
Thanks.


Takashi


> 
> 
> Best regards
> 
> Timo Wischer
> 
> Advanced Driver Information Technology GmbH
> Engineering Software Base (ADITG/ESB)
> Robert-Bosch-Str. 200
> 31139 Hildesheim
> Germany
> 
> Tel. +49 5121 49 6938
> Fax +49 5121 49 6999
> twischer@de.adit-jv.com
> 
> ADIT is a joint venture company of Robert Bosch GmbH/Robert Bosch Car Multimedia GmbH and DENSO Corporation
> Sitz: Hildesheim, Registergericht: Amtsgericht Hildesheim HRB 3438
> Geschäftsführung: Wilhelm Grabow, Ken Yaguchi
> 
> ________________________________________
> From: Takashi Iwai [tiwai@suse.de]
> Sent: Thursday, October 05, 2017 3:17 PM
> To: Wischer, Timo (ADITG/ESB)
> Cc: alsa-devel@alsa-project.org
> Subject: Re: [alsa-devel] SEGFault when optininal       snd_ctl_ext_callback::read_event() not set
> 
> On Thu, 05 Oct 2017 14:03:14 +0200,
> Wischer, Timo (ADITG/ESB) wrote:
> >
> > Hi all,
> >
> > snd_ctl_ext_callback::read_event() callback is mentioned as optional
> > (see http://git.alsa-project.org/?p=alsa-lib.git;a=blob;f=include/control_external.h;h=12958e70a5230de9c74029c641a395a2073c8646;hb=refs/heads/master#l239)
> >
> > but there is no NULL check and the NULL pointer will be called if the read_event function callback pointer is not set.
> > (see http://git.alsa-project.org/?p=alsa-lib.git;a=blob;f=src/control/control_ext.c;h=56552fa1aa0ef0e6383abf4029b63944a841c2c4;hb=refs/heads/master#l419)
> >
> > I think a default function has to be provided which will be called when the callback is not set or the read_event() callback should not be marked as optional.
> >
> > What is your opinion?
> 
> It should have a NULL check there, as documentation clearly states
> that it's optional.
> 
> Care to submit a fix patch?
> 
> 
> thanks,
> 
> Takashi
> From 8cc3dbc6fad0a4de82ab4b5c95a86499c99d56d8 Mon Sep 17 00:00:00 2001
> From: Timo Wischer <twischer@de.adit-jv.com>
> Date: Thu, 5 Oct 2017 16:25:23 +0200
> Subject: ctl: ext: Fail with error code if snd_ctl_ext_callback::read_event()
>  callback is not defined
> 
> The snd_ctl_ext_callback::read_event() callback is only optional
> if no poll descriptor was given via
> snd_ctl_ext_t::poll_fd
> or
> snd_ctl_ext_callback::snd_ctl_ext_poll_descriptors().
> 
> If a poll descriptor is given the
> snd_ctl_ext_callback::read_event()
> callback has also to be defined
> because there is no minigful default behavior.
> 
> This callback will be called when ever the poll() on
> the file descriptor indicates that there is an event pending.
> Therefore returning a 0 which indicates that there is no event makes no
> sense.
> 
> Signed-off-by: Timo Wischer <twischer@de.adit-jv.com>
> 
> diff --git a/src/control/control_ext.c b/src/control/control_ext.c
> index 56552fa..d7de8e8 100644
> --- a/src/control/control_ext.c
> +++ b/src/control/control_ext.c
> @@ -415,8 +415,12 @@ static int snd_ctl_ext_read(snd_ctl_t *handle, snd_ctl_event_t *event)
>  {
>  	snd_ctl_ext_t *ext = handle->private_data;
>  
> -	memset(event, 0, sizeof(*event));
> -	return ext->callback->read_event(ext, &event->data.elem.id, &event->data.elem.mask);
> +	if (ext->callback->read_event) {
> +		memset(event, 0, sizeof(*event));
> +		return ext->callback->read_event(ext, &event->data.elem.id, &event->data.elem.mask);
> +	}
> +
> +	return -EINVAL;
>  }
>  
>  static int snd_ctl_ext_poll_descriptors_count(snd_ctl_t *handle)

Patch
diff mbox

From 8cc3dbc6fad0a4de82ab4b5c95a86499c99d56d8 Mon Sep 17 00:00:00 2001
From: Timo Wischer <twischer@de.adit-jv.com>
Date: Thu, 5 Oct 2017 16:25:23 +0200
Subject: ctl: ext: Fail with error code if snd_ctl_ext_callback::read_event()
 callback is not defined

The snd_ctl_ext_callback::read_event() callback is only optional
if no poll descriptor was given via
snd_ctl_ext_t::poll_fd
or
snd_ctl_ext_callback::snd_ctl_ext_poll_descriptors().

If a poll descriptor is given the
snd_ctl_ext_callback::read_event()
callback has also to be defined
because there is no minigful default behavior.

This callback will be called when ever the poll() on
the file descriptor indicates that there is an event pending.
Therefore returning a 0 which indicates that there is no event makes no
sense.

Signed-off-by: Timo Wischer <twischer@de.adit-jv.com>

diff --git a/src/control/control_ext.c b/src/control/control_ext.c
index 56552fa..d7de8e8 100644
--- a/src/control/control_ext.c
+++ b/src/control/control_ext.c
@@ -415,8 +415,12 @@  static int snd_ctl_ext_read(snd_ctl_t *handle, snd_ctl_event_t *event)
 {
 	snd_ctl_ext_t *ext = handle->private_data;
 
-	memset(event, 0, sizeof(*event));
-	return ext->callback->read_event(ext, &event->data.elem.id, &event->data.elem.mask);
+	if (ext->callback->read_event) {
+		memset(event, 0, sizeof(*event));
+		return ext->callback->read_event(ext, &event->data.elem.id, &event->data.elem.mask);
+	}
+
+	return -EINVAL;
 }
 
 static int snd_ctl_ext_poll_descriptors_count(snd_ctl_t *handle)