[PATCH] usb: atm: ueagle-atm: fix use-after-free in uea_upload_pre_firmware

[Yuhong Cheng <ceohunk@gmail.com>]

syzbot reported a slab-use-after-free read in uea_upload_pre_firmware. This is because the usb_device is passed as context to request_firmware_nowait but its reference count is not incremented. Thus, if the USB device is disconnected before the firmware load completes, the callback accesses a freed usb_device.

Fix this by taking a reference with usb_get_dev() before calling request_firmware_nowait() and releasing it with usb_put_dev() in the completion callback or if the request fails to start.

Reported-by: syzbot+123456@syzkaller.appspotmail.com
---
 drivers/usb/atm/ueagle-atm.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/usb/atm/ueagle-atm.c b/drivers/usb/atm/ueagle-atm.c
index d610cdcef..eaf2f2d3a 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);
 }
 
 /*
@@ -693,13 +694,16 @@ 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;
 }
-- 
2.46.0.windows.1