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

(cherry picked from commit 836b34a935abc91e13e63053d0a83b24dfb5ea78)

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 <tiwai@suse.de>

[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
Reported-by: Ralf Spenneberg <ralf@spenneberg.net>
Cc: <stable@vger.kernel.org> # see the note above
Signed-off-by: Vladis Dronov <vdronov@redhat.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Change-Id: I7073a17d8c99886d2f6ed7981892712ba7dd5873
Bug: 30952477

2 files changed, 9 insertions, 1 deletions

diff --git a/sound/usb/quirks.c b/sound/usb/quirks.c
index 79e2d9ef0b76..65f43a30f4a2 100644
--- a/sound/usb/quirks.c
+++ b/sound/usb/quirks.c
@@ -136,6 +136,7 @@ static int create_fixed_stream_quirk(struct snd_usb_audio *chip,
 		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;
@@ -171,6 +172,7 @@ static int create_fixed_stream_quirk(struct snd_usb_audio *chip,
 	return 0;
 
  error:
+	list_del(&fp->list); /* unlink for avoiding double-free */
 	kfree(fp);
 	kfree(rate_table);
 	return err;
@@ -240,6 +242,7 @@ static int create_uaxx_quirk(struct snd_usb_audio *chip,
 	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:
@@ -263,6 +266,7 @@ static int create_uaxx_quirk(struct snd_usb_audio *chip,
 		? 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;
 	}
diff --git a/sound/usb/stream.c b/sound/usb/stream.c
index 7db2f8958e79..97e678ba194e 100644
--- a/sound/usb/stream.c
+++ b/sound/usb/stream.c
@@ -307,7 +307,9 @@ static struct snd_pcm_chmap_elem *convert_chmap(int channels, unsigned int bits,
 /*
  * 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,
@@ -643,6 +645,7 @@ int snd_usb_parse_audio_interface(struct snd_usb_audio *chip, int iface_no)
 		fp->attributes = parse_uac_endpoint_attributes(chip, alts, protocol, iface_no);
 		fp->clock = clock;
 		fp->chmap = convert_chmap(num_channels, chconfig, protocol);
+		INIT_LIST_HEAD(&fp->list);
 
 		/* some quirks for attributes here */
 
@@ -687,6 +690,7 @@ int snd_usb_parse_audio_interface(struct snd_usb_audio *chip, int iface_no)
 		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);