[PATCH 3.14 30/76] ALSA: usb-audio: Fix double-free in error paths after snd_usb_add_audio_stream() call

From: Greg Kroah-Hartman
Date: Sun Apr 10 2016 - 15:36:34 EST


3.14-stable review patch. If anyone has any objections, please let me know.

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

From: Vladis Dronov <vdronov@xxxxxxxxxx>

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@xxxxxxx>

[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@xxxxxxxxxxxxxx>
Signed-off-by: Vladis Dronov <vdronov@xxxxxxxxxx>
Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
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
@@ -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;
}
--- a/sound/usb/stream.c
+++ b/sound/usb/stream.c
@@ -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);