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Patch "ALSA: usb-audio: Fix double-free in error paths after snd_usb_add_audio_stream() call" has been added to the 3.14-stable tree

PATCH [email protected] 1 participant 1 message Apr 9, 2016

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This is a note to let you know that I've just added the patch titled

ALSA: usb-audio: Fix double-free in error paths after snd_usb_add_audio_stream() call

to the 3.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
alsa-usb-audio-fix-double-free-in-error-paths-after-snd_usb_add_audio_stream-call.patch
and it can be found in the queue-3.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

Quoted 1 line

From 836b34a935abc91e13e63053d0a83b24dfb5ea78 Mon Sep 17 00:00:00 2001

From: Vladis Dronov <[email protected]>
Date: Thu, 31 Mar 2016 12:05:43 -0400
Subject: ALSA: usb-audio: Fix double-free in error paths after snd_usb_add_audio_stream() call

From: Vladis Dronov <[email protected]>

commit 836b34a935abc91e13e63053d0a83b24dfb5ea78 upstream.

create_fixed_stream_quirk(), snd_usb_parse_audio_interface() and create_uaxx_quirk() functions allocate the audioformat object by themselves and free it upon error before returning. However, once the object is linked to a stream, it's freed again in snd_usb_audio_pcm_free(), thus it'll be double-freed, eventually resulting in a memory corruption.

This patch fixes these failures in the error paths by unlinking the audioformat object before freeing it.

Based on a patch by Takashi Iwai <[email protected]>

[Note for stable backports:
this patch requires the commit 902eb7fd1e4a ('ALSA: usb-audio: Minor code cleanup in create_fixed_stream_quirk()')]

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1283358

---
 sound/usb/quirks.c |    4 ++++
 sound/usb/stream.c |    6 +++++-
 2 files changed, 9 insertions(+), 1 deletion(-)
sound/usb/quirks.c +4 -0
@@ -138,6 +138,7 @@ static int create_fixed_stream_quirk(str
 		snd_printk(KERN_ERR "cannot memdup\n");
 		return -ENOMEM;
 	}
+	INIT_LIST_HEAD(&fp->list);
 	if (fp->nr_rates > MAX_NR_RATES) {
 		kfree(fp);
 		return -EINVAL;
@@ -181,6 +182,7 @@ static int create_fixed_stream_quirk(str
 	return 0;
 
  error:
+	list_del(&fp->list); /* unlink for avoiding double-free */
 	kfree(fp);
 	kfree(rate_table);
 	return err;
@@ -456,6 +458,7 @@ static int create_uaxx_quirk(struct snd_
 	fp->ep_attr = get_endpoint(alts, 0)->bmAttributes;
 	fp->datainterval = 0;
 	fp->maxpacksize = le16_to_cpu(get_endpoint(alts, 0)->wMaxPacketSize);
+	INIT_LIST_HEAD(&fp->list);
 
 	switch (fp->maxpacksize) {
 	case 0x120:
@@ -479,6 +482,7 @@ static int create_uaxx_quirk(struct snd_
 		? SNDRV_PCM_STREAM_CAPTURE : SNDRV_PCM_STREAM_PLAYBACK;
 	err = snd_usb_add_audio_stream(chip, stream, fp);
 	if (err < 0) {
+		list_del(&fp->list); /* unlink for avoiding double-free */
 		kfree(fp);
 		return err;
 	}
sound/usb/stream.c +5 -1
@@ -315,7 +315,9 @@ static struct snd_pcm_chmap_elem *conver
 /*
  * add this endpoint to the chip instance.
  * if a stream with the same endpoint already exists, append to it.
- * if not, create a new pcm stream.
+ * if not, create a new pcm stream. note, fp is added to the substream
+ * fmt_list and will be freed on the chip instance release. do not free
+ * fp or do remove it from the substream fmt_list to avoid double-free.
  */
 int snd_usb_add_audio_stream(struct snd_usb_audio *chip,
 			     int stream,
@@ -662,6 +664,7 @@ int snd_usb_parse_audio_interface(struct
 					* (fp->maxpacksize & 0x7ff);
 		fp->attributes = parse_uac_endpoint_attributes(chip, alts, protocol, iface_no);
 		fp->clock = clock;
+		INIT_LIST_HEAD(&fp->list);
 
 		/* some quirks for attributes here */
 
@@ -710,6 +713,7 @@ int snd_usb_parse_audio_interface(struct
 		snd_printdd(KERN_INFO "%d:%u:%d: add audio endpoint %#x\n", dev->devnum, iface_no, altno, fp->endpoint);
 		err = snd_usb_add_audio_stream(chip, stream, fp);
 		if (err < 0) {
+			list_del(&fp->list); /* unlink for avoiding double-free */
 			kfree(fp->rate_table);
 			kfree(fp->chmap);
 			kfree(fp);

Patches currently in stable-queue which might be from [email protected] are

queue-3.14/alsa-usb-audio-fix-double-free-in-error-paths-after-snd_usb_add_audio_stream-call.patch