[PATCH] ALSA: caiaq: Decoupling ep1_in_urb in caiaq dev

[Edward Adam Davis]

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).

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.

[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
 
Reported-by: syzbot+832ce9fa3face1b7d44d@xxxxxxxxxxxxxxxxxxxxxxxxx
Fixes: 523f1dce3743 ("[ALSA] Add Native Instrument usb audio device support")
Closes: https://syzkaller.appspot.com/bug?extid=832ce9fa3face1b7d44d
Tested-by: syzbot+832ce9fa3face1b7d44d@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Edward Adam Davis <eadavis@xxxxxxxx>
---
 sound/usb/caiaq/device.c | 19 +++++++++++--------
 sound/usb/caiaq/device.h |  2 +-
 2 files changed, 12 insertions(+), 9 deletions(-)

diff --git a/sound/usb/caiaq/device.c b/sound/usb/caiaq/device.c
index a16e59248480..138b58914f1c 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;
+	ret = usb_submit_urb(cdev->ep1_in_urb, GFP_ATOMIC);
 	if (ret < 0)
 		dev_err(dev, "unable to submit urb. OOM!?\n");
 }
@@ -408,6 +408,8 @@ 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;
 }
 
 static int create_card(struct usb_device *usb_dev,
@@ -457,10 +459,11 @@ static int init_card(struct snd_usb_caiaqdev *cdev)
 		return -EIO;
 	}
 
-	usb_init_urb(&cdev->ep1_in_urb);
+	cdev->ep1_in_urb = usb_alloc_urb(0, GFP_KERNEL);
+	usb_init_urb(cdev->ep1_in_urb);
 	usb_init_urb(&cdev->midi_out_urb);
 
-	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);
@@ -471,7 +474,7 @@ static int init_card(struct snd_usb_caiaqdev *cdev)
 			  snd_usb_caiaq_midi_output_done, cdev);
 
 	/* sanity checks of EPs before actually submitting */
-	if (usb_urb_ep_type_check(&cdev->ep1_in_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 +483,7 @@ 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 +533,7 @@ 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;
 }
 
@@ -576,7 +579,7 @@ 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->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..a5f7dada25d8 100644
--- a/sound/usb/caiaq/device.h
+++ b/sound/usb/caiaq/device.h
@@ -60,7 +60,7 @@ struct snd_usb_caiaq_cb_info;
 struct snd_usb_caiaqdev {
 	struct snd_usb_audio chip;
 
-	struct urb ep1_in_urb;
+	struct urb *ep1_in_urb;
 	struct urb midi_out_urb;
 	struct urb **data_urbs_in;
 	struct urb **data_urbs_out;
-- 
2.43.0