linux-kernel - Re: [PATCH] ALSA: usb-audio: Fix a potential memory leak in scarlett2_init

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Date:   Sun, 3 Sep 2023 21:42:55 +0200
From:   Christophe JAILLET <christophe.jaillet@...adoo.fr>
To:     Takashi Iwai <tiwai@...e.de>
Cc:     Jaroslav Kysela <perex@...ex.cz>, Takashi Iwai <tiwai@...e.com>,
        linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org,
        alsa-devel@...a-project.org
Subject: Re: [PATCH] ALSA: usb-audio: Fix a potential memory leak in
 scarlett2_init_notify()

Le 03/09/2023 à 18:37, Takashi Iwai a écrit :
> On Sun, 03 Sep 2023 17:04:47 +0200,
...

> Indeed.  The fix would be rather a oneliner like below, though:

Looks much better than mine :)

I let you send the patch, it is your solution.

Just for my understanding, how is snd_ump_ops used, especially .open?
I've not been able to figure out where it was called.

In alloc_midi_urbs(), if usb_alloc_coherent() fails, then 
ctx->urb->transfer_buffer could be anything because usb_fill_xxx_urb() 
is not called.
So there could be an edge case where your fix could still be incomplete.

For the start_input_streams() caller, this is fine, because the 
corresponding memory is kzalloc()'ed in start_input_streams() at some 
point, but I've not been able to check for snd_usb_midi_v2_open().

CJ

> 
> --- a/sound/usb/midi2.c
> +++ b/sound/usb/midi2.c
> @@ -265,7 +265,7 @@ static void free_midi_urbs(struct snd_usb_midi2_endpoint *ep)
>   
>   	if (!ep)
>   		return;
> -	for (i = 0; i < ep->num_urbs; ++i) {
> +	for (i = 0; i < NUM_URBS; ++i) {
>   		ctx = &ep->urbs[i];
>   		if (!ctx->urb)
>   			break;
> 
> That was the intended behavior of free_midi_urbs().
> 
> 
> Takashi
>