This is a note to let you know that I've just added the patch titled ALSA: line6: Fix racy initialization of LINE6 MIDI to the 4.9-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: alsa-line6-fix-racy-initialization-of-line6-midi.patch and it can be found in the queue-4.9 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From 05ca447630334c323c9e2b788b61133ab75d60d3 Mon Sep 17 00:00:00 2001 From: Takashi Iwai <tiwai@xxxxxxx> Date: Tue, 18 May 2021 10:39:39 +0200 Subject: ALSA: line6: Fix racy initialization of LINE6 MIDI From: Takashi Iwai <tiwai@xxxxxxx> 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@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx Link: https://lore.kernel.org/r/000000000000a4be9405c28520de@xxxxxxxxxx Link: https://lore.kernel.org/r/20210517132725.GA50495@hyeyoo Cc: Hyeonggon Yoo <42.hyeyoo@xxxxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> Link: https://lore.kernel.org/r/20210518083939.1927-1-tiwai@xxxxxxx Signed-off-by: Takashi Iwai <tiwai@xxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- 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 @@ -687,6 +687,10 @@ 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; Patches currently in stable-queue which might be from tiwai@xxxxxxx are queue-4.9/alsa-line6-fix-racy-initialization-of-line6-midi.patch