sound/core/seq: Initialize structure pointer to NULL to prevent undefined behavior

[PATCH] sound/core/seq: Initialize structure pointer to NULL to prevent undefined behavior

Posted by hariconscious@gmail.com 4 months, 1 week ago

From: HariKrishna Sagala <hariconscious@gmail.com>

This change ensures the structure pointer is explicitly initialized to
NULL,preventing potential access to uninitialized memory. It improves
code safety and avoids undefined behavior during pointer dereferencing.

Signed-off-by: HariKrishna Sagala <hariconscious@gmail.com>
---

Note:
Turned on the settings needed for sequencer MIDI and built a kernel
image with those settings. The system booted up fine with no errors.
However, couldn’t get the sequencer emulation to start.

 sound/core/seq/seq_midi_emul.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/sound/core/seq/seq_midi_emul.c b/sound/core/seq/seq_midi_emul.c
index 81d2ef5e5811..f24c5a475c41 100644
--- a/sound/core/seq/seq_midi_emul.c
+++ b/sound/core/seq/seq_midi_emul.c
@@ -647,7 +647,7 @@ static void snd_midi_channel_init(struct snd_midi_channel *p, int n)
  */
 static struct snd_midi_channel *snd_midi_channel_init_set(int n)
 {
-	struct snd_midi_channel *chan;
+	struct snd_midi_channel *chan = NULL;
 	int  i;
 
 	chan = kmalloc_array(n, sizeof(struct snd_midi_channel), GFP_KERNEL);
@@ -686,7 +686,7 @@ reset_all_channels(struct snd_midi_channel_set *chset)
  */
 struct snd_midi_channel_set *snd_midi_channel_alloc_set(int n)
 {
-	struct snd_midi_channel_set *chset;
+	struct snd_midi_channel_set *chset = NULL;
 
 	chset = kmalloc(sizeof(*chset), GFP_KERNEL);
 	if (chset) {

base-commit: 50c19e20ed2ef359cf155a39c8462b0a6351b9fa
-- 
2.43.0

Re: [PATCH] sound/core/seq: Initialize structure pointer to NULL to prevent undefined behavior

Posted by David Hunter 4 months ago

On 10/2/25 13:43, hariconscious@gmail.com wrote:
> From: HariKrishna Sagala <hariconscious@gmail.com>
> 
> This change ensures the structure pointer is explicitly initialized to
> NULL,preventing potential access to uninitialized memory. It improves
> code safety and avoids undefined behavior during pointer dereferencing.
> 
> Signed-off-by: HariKrishna Sagala <hariconscious@gmail.com>

Hi Harikrishna,

Thank you for detailing your attempt at testing. Unfortunately, your
patch makes no substantive change. The variable you are setting to NULL
is assigned before use, so there is no risk of undefined behavior.

I know this can seem discouraging to hear, but I do want you to
encourage you to keep looking for ways you can make contributions.

Thanks,
David

Re: [PATCH] sound/core/seq: Initialize structure pointer to NULL to prevent undefined behavior

Posted by Takashi Iwai 4 months, 1 week ago

On Thu, 02 Oct 2025 19:43:00 +0200,
hariconscious@gmail.com wrote:
> 
> From: HariKrishna Sagala <hariconscious@gmail.com>
> 
> This change ensures the structure pointer is explicitly initialized to
> NULL,preventing potential access to uninitialized memory. It improves
> code safety and avoids undefined behavior during pointer dereferencing.
> 
> Signed-off-by: HariKrishna Sagala <hariconscious@gmail.com>
> ---
> 
> Note:
> Turned on the settings needed for sequencer MIDI and built a kernel
> image with those settings. The system booted up fine with no errors.
> However, couldn’t get the sequencer emulation to start.

Something really wrong in your test, I'm afraid.
See your patch below more closely:

> 
>  sound/core/seq/seq_midi_emul.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/sound/core/seq/seq_midi_emul.c b/sound/core/seq/seq_midi_emul.c
> index 81d2ef5e5811..f24c5a475c41 100644
> --- a/sound/core/seq/seq_midi_emul.c
> +++ b/sound/core/seq/seq_midi_emul.c
> @@ -647,7 +647,7 @@ static void snd_midi_channel_init(struct snd_midi_channel *p, int n)
>   */
>  static struct snd_midi_channel *snd_midi_channel_init_set(int n)
>  {
> -	struct snd_midi_channel *chan;
> +	struct snd_midi_channel *chan = NULL;
>  	int  i;
>  
>  	chan = kmalloc_array(n, sizeof(struct snd_midi_channel), GFP_KERNEL);

The variable chan is initialized at the very beginning.
NULL initialization is utterly nonsense.

> @@ -686,7 +686,7 @@ reset_all_channels(struct snd_midi_channel_set *chset)
>   */
>  struct snd_midi_channel_set *snd_midi_channel_alloc_set(int n)
>  {
> -	struct snd_midi_channel_set *chset;
> +	struct snd_midi_channel_set *chset = NULL;
>  
>  	chset = kmalloc(sizeof(*chset), GFP_KERNEL);

Here, too.

So all changes make really no sense.


thanks,

Takashi