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Subject[PATCH 3.2 063/115] ALSA: usb-audio: Fix double-free in error paths after snd_usb_add_audio_stream() call
3.2.80-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Vladis Dronov <vdronov@redhat.com>

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 <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>
Signed-off-by: Vladis Dronov <vdronov@redhat.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
sound/usb/quirks.c | 4 ++++
sound/usb/stream.c | 6 +++++-
2 files changed, 9 insertions(+), 1 deletion(-)

--- a/sound/usb/quirks.c
+++ b/sound/usb/quirks.c
@@ -136,6 +136,7 @@ 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;
@@ -174,6 +175,7 @@ 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;
@@ -243,6 +245,7 @@ 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:
@@ -266,6 +269,7 @@ 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;
}
--- a/sound/usb/stream.c
+++ b/sound/usb/stream.c
@@ -77,7 +77,9 @@ static void snd_usb_audio_pcm_free(struc
/*
* 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,
@@ -403,6 +405,7 @@ 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 */

@@ -446,6 +449,7 @@ 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);
return err;
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