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[83.28.44.95]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-49cee5dadddsm75695255e9.9.2026.09.03.04.34.11 (version=TLS1_2 cipher=AES128-SHA bits=128/128); Thu, 03 Sep 2026 04:34:12 -0700 (PDT) Date: Thu, 3 Sep 2026 13:34:08 +0200 From: Michal Pecio To: Edward Adam Davis Cc: daniel@caiaq.org, gregkh@linuxfoundation.org, linux-kernel@vger.kernel.org, linux-sound@vger.kernel.org, linux-usb@vger.kernel.org, perex@perex.cz, syzbot+832ce9fa3face1b7d44d@syzkaller.appspotmail.com, syzkaller-bugs@googlegroups.com, tiwai@suse.com, tiwai@suse.de, zonque@gmail.com Subject: Re: [PATCH v2] ALSA: caiaq: Decoupling ep1_in_urb in caiaq dev Message-ID: <20260903133408.7da4c35f.michal.pecio@gmail.com> In-Reply-To: <20260903100410.541828-1-eadavis@sina.com> References: <20260903094105.539519-1-eadavis@sina.com> <20260903100410.541828-1-eadavis@sina.com> Precedence: bulk X-Mailing-List: linux-usb@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Thu, 3 Sep 2026 18:04:10 +0800, Edward Adam Davis wrote: > The epq_in_urb object belonging to the caiaq device is coupled within > the struct snd_usb_caiaqdev. After usb_submit_urb(epq_in_urb, GFP_KERNEL) > executes successfully, epq_in_urb is successfully added to the urbp_list > queue of the dummy HCD driver (userspace specifies dummy_hcd as the HCD > layer driver for the caiaq USB device). Sounds like an irrelevant detail. Same crash would happen with any HCD. > When init_card() calls snd_usb_caiaq_send_command() which subsequently > fails due to a timeout, and proceeds to call snd_card_free() to release > the card, the embedded ep1_in_urb object is also freed. When the dummy > HCD driver detects that the URB has been unlinked, it returns the URB > (by usb_hcd_giveback_urb()), which triggers [1]. > > Decouple the ep1_in_urb object from the struct snd_usb_caiaqdev and switch > to using a pointer instead. Separately allocate and manage the memory for > ep1_in_urb to prevent the release of the snd_card memory object from > interfering with it. > > midi_out_urb has the same issue as ep1_in_urb and is handled in the same > way. > > [1] > BUG: KASAN: slab-use-after-free in usb_free_urb+0x24/0x120 drivers/usb/core/urb.c:96 > Write of size 4 at addr ffff88803cee1050 by task ktimers/1/29 > Call Trace: > usb_free_urb+0x24/0x120 drivers/usb/core/urb.c:96 > dummy_timer+0xaac/0x4d50 drivers/usb/gadget/udc/dummy_hcd.c:2019 > __run_hrtimer kernel/time/hrtimer.c:2067 [inline] > __hrtimer_run_queues+0x3eb/0xaf0 kernel/time/hrtimer.c:2124 > hrtimer_run_softirq+0x1e1/0x2e0 kernel/time/hrtimer.c:2141 > > Allocated by task 36: > snd_card_new+0x7b/0x110 sound/core/init.c:184 > create_card sound/usb/caiaq/device.c:429 [inline] > snd_probe+0x236/0x1af0 sound/usb/caiaq/device.c:544 > > Freed by task 36: > snd_card_free_when_closed sound/core/init.c:630 [inline] > snd_card_free+0x138/0x1d0 sound/core/init.c:662 > snd_probe+0x162b/0x1af0 sound/usb/caiaq/device.c:553 > > Fixes: 523f1dce3743 ("[ALSA] Add Native Instrument usb audio device support") > Reported-by: syzbot+832ce9fa3face1b7d44d@syzkaller.appspotmail.com > Closes: https://syzkaller.appspot.com/bug?extid=832ce9fa3face1b7d44d > Tested-by: syzbot+832ce9fa3face1b7d44d@syzkaller.appspotmail.com > Signed-off-by: Edward Adam Davis > --- Does this submission comply with the rules here? https://docs.kernel.org/process/coding-assistants.html > v1 -> v2: same dealwith midi_out_urb and add missing check > > sound/usb/caiaq/device.c | 39 +++++++++++++++++++++++++++------------ > sound/usb/caiaq/device.h | 4 ++-- > sound/usb/caiaq/midi.c | 6 +++--- > 3 files changed, 32 insertions(+), 17 deletions(-) > > diff --git a/sound/usb/caiaq/device.c b/sound/usb/caiaq/device.c > index a16e59248480..d0fe954b8133 100644 > --- a/sound/usb/caiaq/device.c > +++ b/sound/usb/caiaq/device.c > @@ -192,8 +192,8 @@ static void usb_ep1_command_reply_dispatch (struct urb* urb) > break; > } > > - cdev->ep1_in_urb.actual_length = 0; > - ret = usb_submit_urb(&cdev->ep1_in_urb, GFP_ATOMIC); > + cdev->ep1_in_urb->actual_length = 0; That's one of the first things usb_submit_urb() below would do, and has done since forever. > + ret = usb_submit_urb(cdev->ep1_in_urb, GFP_ATOMIC); > if (ret < 0) > dev_err(dev, "unable to submit urb. OOM!?\n"); > } > @@ -408,6 +408,10 @@ static void card_free(struct snd_card *card) > #endif > snd_usb_caiaq_audio_free(cdev); > usb_put_dev(cdev->chip.dev); > + usb_free_urb(cdev->ep1_in_urb); > + cdev->ep1_in_urb = NULL; > + usb_free_urb(cdev->midi_out_urb); > + cdev->midi_out_urb = NULL; Is clearing this necessary? (I'm not familiar with ALSA) > } > > static int create_card(struct usb_device *usb_dev, > @@ -457,22 +461,33 @@ static int init_card(struct snd_usb_caiaqdev *cdev) > return -EIO; > } > > - usb_init_urb(&cdev->ep1_in_urb); > - usb_init_urb(&cdev->midi_out_urb); > + cdev->ep1_in_urb = usb_alloc_urb(0, GFP_KERNEL); > + if (!cdev->ep1_in_urb) { > + dev_err(dev, "alloc ep1_in_urb failed.\n"); AFAIK logging on allocation failure is frowned upon. > + return -ENOMEM; > + } > + cdev->midi_out_urb = usb_alloc_urb(0, GFP_KERNEL); > + if (!cdev->midi_out_urb) { > + usb_free_urb(cdev->ep1_in_urb); > + dev_err(dev, "alloc midi_out_urb failed.\n"); > + return -ENOMEM; > + } > + usb_init_urb(cdev->ep1_in_urb); > + usb_init_urb(cdev->midi_out_urb); And what would be the point of that? > > - usb_fill_bulk_urb(&cdev->ep1_in_urb, usb_dev, > + usb_fill_bulk_urb(cdev->ep1_in_urb, usb_dev, > usb_rcvbulkpipe(usb_dev, 0x1), > cdev->ep1_in_buf, EP1_BUFSIZE, > usb_ep1_command_reply_dispatch, cdev); > > - usb_fill_bulk_urb(&cdev->midi_out_urb, usb_dev, > + usb_fill_bulk_urb(cdev->midi_out_urb, usb_dev, > usb_sndbulkpipe(usb_dev, 0x1), > cdev->midi_out_buf, EP1_BUFSIZE, > snd_usb_caiaq_midi_output_done, cdev); > > /* sanity checks of EPs before actually submitting */ > - if (usb_urb_ep_type_check(&cdev->ep1_in_urb) || > - usb_urb_ep_type_check(&cdev->midi_out_urb)) { > + if (usb_urb_ep_type_check(cdev->ep1_in_urb) || > + usb_urb_ep_type_check(cdev->midi_out_urb)) { > dev_err(dev, "invalid EPs\n"); > return -EINVAL; > } > @@ -480,7 +495,7 @@ static int init_card(struct snd_usb_caiaqdev *cdev) > init_waitqueue_head(&cdev->ep1_wait_queue); > init_waitqueue_head(&cdev->prepare_wait_queue); > > - if (usb_submit_urb(&cdev->ep1_in_urb, GFP_KERNEL) != 0) > + if (usb_submit_urb(cdev->ep1_in_urb, GFP_KERNEL) != 0) > return -EIO; > > err = snd_usb_caiaq_send_command(cdev, EP1_CMD_GET_DEVICE_INFO, NULL, 0); > @@ -530,7 +545,7 @@ static int init_card(struct snd_usb_caiaqdev *cdev) > return 0; > > err_kill_urb: > - usb_kill_urb(&cdev->ep1_in_urb); > + usb_kill_urb(cdev->ep1_in_urb); > return err; > } > > @@ -576,8 +591,8 @@ static void snd_disconnect(struct usb_interface *intf) > #endif > snd_usb_caiaq_audio_disconnect(cdev); > > - usb_kill_urb(&cdev->ep1_in_urb); > - usb_kill_urb(&cdev->midi_out_urb); > + usb_kill_urb(cdev->ep1_in_urb); > + usb_kill_urb(cdev->midi_out_urb); > > snd_card_free_when_closed(card); > } > diff --git a/sound/usb/caiaq/device.h b/sound/usb/caiaq/device.h > index 743eb0387b5f..1c6f34693fa8 100644 > --- a/sound/usb/caiaq/device.h > +++ b/sound/usb/caiaq/device.h > @@ -60,8 +60,8 @@ struct snd_usb_caiaq_cb_info; > struct snd_usb_caiaqdev { > struct snd_usb_audio chip; > > - struct urb ep1_in_urb; > - struct urb midi_out_urb; > + struct urb *ep1_in_urb; > + struct urb *midi_out_urb; > struct urb **data_urbs_in; > struct urb **data_urbs_out; > struct snd_usb_caiaq_cb_info *data_cb_info; > diff --git a/sound/usb/caiaq/midi.c b/sound/usb/caiaq/midi.c > index c656d0162432..18529484c8dc 100644 > --- a/sound/usb/caiaq/midi.c > +++ b/sound/usb/caiaq/midi.c > @@ -43,7 +43,7 @@ static int snd_usb_caiaq_midi_output_close(struct snd_rawmidi_substream *substre > { > struct snd_usb_caiaqdev *cdev = substream->rmidi->private_data; > if (cdev->midi_out_active) { > - usb_kill_urb(&cdev->midi_out_urb); > + usb_kill_urb(cdev->midi_out_urb); > cdev->midi_out_active = 0; > } > return 0; > @@ -64,9 +64,9 @@ static void snd_usb_caiaq_midi_send(struct snd_usb_caiaqdev *cdev, > return; > > cdev->midi_out_buf[2] = len; > - cdev->midi_out_urb.transfer_buffer_length = len+3; > + cdev->midi_out_urb->transfer_buffer_length = len+3; > > - ret = usb_submit_urb(&cdev->midi_out_urb, GFP_ATOMIC); > + ret = usb_submit_urb(cdev->midi_out_urb, GFP_ATOMIC); > if (ret < 0) > dev_err(dev, > "snd_usb_caiaq_midi_send(%p): usb_submit_urb() failed," > -- > 2.43.0 >