Re: [PATCH] ALSA: usb-audio: Fix double-free in snd_usb_add_audio_stream()

[Takashi Iwai]

On Wed, 30 Mar 2016 21:03:22 +0200,
Vladis Dronov wrote:
> 
> There is a double-free bug in [snd-usb-audio] module due to alloc/free logic
> flaw in snd_usb_add_audio_stream() function. This leads to kernel structures
> corruption and panic. Fix the code flow and alloc/free logic so there is no
> double-free.
> 
> The detailed analysis: https://bugzilla.redhat.com/show_bug.cgi?id=1283358
> 
> Reported-by: Ralf Spenneberg <r...@spenneberg.net>
> Signed-off-by: Vladis Dronov <vdro...@redhat.com>

Thanks for the report.  But how about a simpler fix like below?


Takashi

---
diff --git a/sound/usb/quirks.c b/sound/usb/quirks.c
index fb62bce2435c..0e154ae7924e 100644
--- a/sound/usb/quirks.c
+++ b/sound/usb/quirks.c
@@ -150,6 +150,7 @@ static int create_fixed_stream_quirk(struct snd_usb_audio 
*chip,
                usb_audio_err(chip, "cannot memdup\n");
                return -ENOMEM;
        }
+       INIT_LIST_HEAD(&fp->list);
        if (fp->nr_rates > MAX_NR_RATES) {
                kfree(fp);
                return -EINVAL;
@@ -193,8 +194,11 @@ static int create_fixed_stream_quirk(struct snd_usb_audio 
*chip,
        return 0;
 
  error:
-       kfree(fp);
-       kfree(rate_table);
+       /* linked fp will be removed in snd_usb_audio_pcm_free() */
+       if (list_empty(&fp->list)) {
+               kfree(fp);
+               kfree(rate_table);
+       }
        return err;
 }