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

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>

diff --git a/sound/usb/quirks.c b/sound/usb/quirks.c
index fb62bce..6178bb5 100644 (file)
--- 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;
@@ -193,6 +194,7 @@ 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;
@@ -469,6 +471,7 @@ 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:
@@ -492,6 +495,7 @@ 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 c4dc577..8e9548b 100644 (file)
--- a/sound/usb/stream.c
+++ b/sound/usb/stream.c
@@ -314,7 +314,9 @@ 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,
@@ -675,6 +677,7 @@ int snd_usb_parse_audio_interface(struct snd_usb_audio *chip, int iface_no)
                                        * (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 */
 
@@ -723,6 +726,7 @@ int snd_usb_parse_audio_interface(struct snd_usb_audio *chip, int iface_no)
                dev_dbg(&dev->dev, "%u:%d: add audio endpoint %#x\n", 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);