Re: [PATCH] ALSA: usb-audio: Fix a potential memory leak in scarlett2_init_notify()

Christophe JAILLET
2023-09-03T15:04:59Z

Le 03/09/2023 à 16:23, Takashi Iwai a écrit :
> On Sun, 03 Sep 2023 15:06:00 +0200,
> Christophe JAILLET wrote:
>>
>> If usb_alloc_coherent() or usb_urb_ep_type_check() fail, we should release
>> the resources previously allocated.
>
> Those are freed in the caller side, start_input_streams() instead.

Thanks for the fast review.

Hmpm, If IIUC, resources allocated *before* the ending "ep->num_urbs++"
still need to be freed here, otherwise free_midi_urbs() in the caller
will not free them.

Do you agree?

If yes, I can send v2 which would look like:
usb_alloc_urb()
if (err)
return -ENOMEM

usb_alloc_coherent()
if (err) {
usb_free_urb()
urb = NULL
return -ENOMEM
}

usb_urb_ep_type_check()
if (err) {
usb_free_coherent()
usb_free_urb()
urb = NULL
return -err
}

Or, if yuo prefer, with an error handling path just like below, but
without the final free_midi_urbs() + a comment explaining that the
caller does this part of job instead.

CJ

>
>
> thanks,
>
> Takashi
>
>>
>> Fixes: ff49d1df79ae ("ALSA: usb-audio: USB MIDI 2.0 UMP support")
>> Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
>> ---
>> sound/usb/midi2.c | 17 ++++++++++++++---
>> 1 file changed, 14 insertions(+), 3 deletions(-)
>>
>> diff --git a/sound/usb/midi2.c b/sound/usb/midi2.c
>> index a27e244650c8..4109c82adff6 100644
>> --- a/sound/usb/midi2.c
>> +++ b/sound/usb/midi2.c
>> @@ -302,7 +302,8 @@ static int alloc_midi_urbs(struct snd_usb_midi2_endpoint *ep)
>> ctx->urb = usb_alloc_urb(0, GFP_KERNEL);
>> if (!ctx->urb) {
>> dev_err(&ep->dev->dev, "URB alloc failed\n");
>> - return -ENOMEM;
>> + err = -ENOMEM;
>> + goto err_free_all;
>> }
>> ctx->ep = ep;
>> buffer = usb_alloc_coherent(ep->dev, len, GFP_KERNEL,
>> @@ -310,7 +311,8 @@ static int alloc_midi_urbs(struct snd_usb_midi2_endpoint *ep)
>> if (!buffer) {
>> dev_err(&ep->dev->dev,
>> "URB buffer alloc failed (size %d)\n", len);
>> - return -ENOMEM;
>> + err = -ENOMEM;
>> + goto err_free_cur_urb;
>> }
>> if (ep->interval)
>> usb_fill_int_urb(ctx->urb, ep->dev, ep->pipe,
>> @@ -322,13 +324,22 @@ static int alloc_midi_urbs(struct snd_usb_midi2_endpoint *ep)
>> if (err < 0) {
>> dev_err(&ep->dev->dev, "invalid MIDI EP %x\n",
>> endpoint);
>> - return err;
>> + goto err_free_cur_dma;
>> }
>> ctx->urb->transfer_flags = URB_NO_TRANSFER_DMA_MAP;
>> ep->num_urbs++;
>> }
>> ep->urb_free = ep->urb_free_mask = GENMASK(ep->num_urbs - 1, 0);
>> return 0;
>> +
>> +err_free_cur_dma:
>> + usb_free_coherent(ep->dev, len, buffer, ctx->urb->transfer_dma);
>> +err_free_cur_urb:
>> + usb_free_urb(ctx->urb);
>> + ctx->urb = NULL;
>> +err_free_all:
>> + free_midi_urbs(ep);
>> + return err;
>> }
>>
>> static struct snd_usb_midi2_endpoint *
>> --
>> 2.34.1
>>
>