uea_load_firmware() calls request_firmware_nowait() passing a raw
struct usb_device pointer as context, without holding a reference
to it.

If the USB device is disconnected before the firmware workqueue
fires, the usb_device and its usb_interface objects are freed while
uea_upload_pre_firmware() is still pending on the workqueue. When
the callback eventually runs, it accesses the freed memory causing
a slab-use-after-free:

  BUG: KASAN: slab-use-after-free in __intf_to_usbdev
  include/linux/usb.h:752 [inline]
  BUG: KASAN: slab-use-after-free in uea_upload_pre_firmware+0x8d/0x640
  drivers/usb/atm/ueagle-atm.c:598
  Read of size 8 at addr ffff88802b0710b8 by task kworker/0:2/1664

Fix by calling usb_get_dev() before queuing the firmware request to
pin the usb_device in memory for the lifetime of the async operation,
and usb_put_dev() in the callback once it is finished with the
pointer. On the error path where request_firmware_nowait() itself
fails, drop the reference immediately since the callback will never
fire.

Reported-by: syzbot+3d45d763d18796f97412@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=3d45d763d18796f97412
Signed-off-by: Deepanshu Kartikey <redacted>
---
 drivers/usb/atm/ueagle-atm.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/usb/atm/ueagle-atm.c b/drivers/usb/atm/ueagle-atm.c
index d610cdcef7d0..686cc58fb89f 100644
--- a/drivers/usb/atm/ueagle-atm.c
+++ b/drivers/usb/atm/ueagle-atm.c

@@ -663,6 +663,7 @@ static void uea_upload_pre_firmware(const struct firmware *fw_entry,
 	uea_err(usb, "firmware is corrupted\n");
 err:
 	release_firmware(fw_entry);
+	usb_put_dev(usb);
 }
 
 /*

@@ -693,12 +694,14 @@ static int uea_load_firmware(struct usb_device *usb, unsigned int ver)
 		break;
 	}
 
+	usb_get_dev(usb);
 	ret = request_firmware_nowait(THIS_MODULE, 1, fw_name, &usb->dev,
 					GFP_KERNEL, usb,
 					uea_upload_pre_firmware);
-	if (ret)
+	if (ret) {
 		uea_err(usb, "firmware %s is not available\n", fw_name);
-	else
+		usb_put_dev(usb);
+	} else
 		uea_info(usb, "loading firmware %s\n", fw_name);
 
 	return ret;

-- 
2.43.0