[PATCH 4.14 06/37] ALSA: line6: Fix racy initialization of LINE6 MIDI

Greg Kroah-Hartman
2021-05-24T15:43:46Z

From: Takashi Iwai <tiwai@suse.de>

commit 05ca447630334c323c9e2b788b61133ab75d60d3 upstream.

The initialization of MIDI devices that are found on some LINE6
drivers are currently done in a racy way; namely, the MIDI buffer
instance is allocated and initialized in each private_init callback
while the communication with the interface is already started via
line6_init_cap_control() call before that point. This may lead to
Oops in line6_data_received() when a spurious event is received, as
reported by syzkaller.

This patch moves the MIDI initialization to line6_init_cap_control()
as well instead of the too-lately-called private_init for avoiding the
race. Also this reduces slightly more lines, so it's a win-win
change.

Reported-by: syzbot+0d2b3feb0a2887862e06@syzkallerlkml..appspotmail.com
Link: https://lore.kernel.org/r/000000000000a4be9405c28520de@google.com
Link: https://lore.kernel.org/r/20210517132725.GA50495@hyeyoo
Cc: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20210518083939.1927-1-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
sound/usb/line6/driver.c | 4 ++++
sound/usb/line6/pod.c | 5 -----
sound/usb/line6/variax.c | 6 ------
3 files changed, 4 insertions(+), 11 deletions(-)

--- a/sound/usb/line6/driver.c
+++ b/sound/usb/line6/driver.c
@@ -698,6 +698,10 @@ static int line6_init_cap_control(struct
line6->buffer_message = kmalloc(LINE6_MIDI_MESSAGE_MAXLEN, GFP_KERNEL);
if (!line6->buffer_message)
return -ENOMEM;
+
+ ret = line6_init_midi(line6);
+ if (ret < 0)
+ return ret;
} else {
ret = line6_hwdep_init(line6);
if (ret < 0)
--- a/sound/usb/line6/pod.c
+++ b/sound/usb/line6/pod.c
@@ -421,11 +421,6 @@ static int pod_init(struct usb_line6 *li
if (err < 0)
return err;

- /* initialize MIDI subsystem: */
- err = line6_init_midi(line6);
- if (err < 0)
- return err;
-
/* initialize PCM subsystem: */
err = line6_init_pcm(line6, &pod_pcm_properties);
if (err < 0)
--- a/sound/usb/line6/variax.c
+++ b/sound/usb/line6/variax.c
@@ -217,7 +217,6 @@ static int variax_init(struct usb_line6
const struct usb_device_id *id)
{
struct usb_line6_variax *variax = (struct usb_line6_variax *) line6;
- int err;

line6->process_message = line6_variax_process_message;
line6->disconnect = line6_variax_disconnect;
@@ -233,11 +232,6 @@ static int variax_init(struct usb_line6
if (variax->buffer_activate == NULL)
return -ENOMEM;

- /* initialize MIDI subsystem: */
- err = line6_init_midi(&variax->line6);
- if (err < 0)
- return err;
-
/* initiate startup procedure: */
variax_startup1(variax);
return 0;