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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Oliver Neukum <oneukum@suse.com>,
        syzbot+1b2449b7b5dc240d107a@syzkaller.appspotmail.com
Subject: [PATCH 4.19 61/85] usb: cdc-acm: make sure a refcount is taken early enough
Date:   Thu, 22 Aug 2019 10:19:34 -0700
Message-Id: <20190822171733.880332700@linuxfoundation.org>
In-Reply-To: <20190822171731.012687054@linuxfoundation.org>
References: <20190822171731.012687054@linuxfoundation.org>
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From: Oliver Neukum <oneukum@suse.com>

commit c52873e5a1ef72f845526d9f6a50704433f9c625 upstream.

destroy() will decrement the refcount on the interface, so that
it needs to be taken so early that it never undercounts.

Fixes: 7fb57a019f94e ("USB: cdc-acm: Fix potential deadlock (lockdep warning)")
Cc: stable <stable@vger.kernel.org>
Reported-and-tested-by: syzbot+1b2449b7b5dc240d107a@syzkaller.appspotmail.com
Signed-off-by: Oliver Neukum <oneukum@suse.com>
Link: https://lore.kernel.org/r/20190808142119.7998-1-oneukum@suse.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/usb/class/cdc-acm.c |   12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

--- a/drivers/usb/class/cdc-acm.c
+++ b/drivers/usb/class/cdc-acm.c
@@ -1333,10 +1333,6 @@ made_compressed_probe:
 	tty_port_init(&acm->port);
 	acm->port.ops = &acm_port_ops;
 
-	minor = acm_alloc_minor(acm);
-	if (minor < 0)
-		goto alloc_fail1;
-
 	ctrlsize = usb_endpoint_maxp(epctrl);
 	readsize = usb_endpoint_maxp(epread) *
 				(quirks == SINGLE_RX_URB ? 1 : 2);
@@ -1344,6 +1340,13 @@ made_compressed_probe:
 	acm->writesize = usb_endpoint_maxp(epwrite) * 20;
 	acm->control = control_interface;
 	acm->data = data_interface;
+
+	usb_get_intf(acm->control); /* undone in destruct() */
+
+	minor = acm_alloc_minor(acm);
+	if (minor < 0)
+		goto alloc_fail1;
+
 	acm->minor = minor;
 	acm->dev = usb_dev;
 	if (h.usb_cdc_acm_descriptor)
@@ -1490,7 +1493,6 @@ skip_countries:
 	usb_driver_claim_interface(&acm_driver, data_interface, acm);
 	usb_set_intfdata(data_interface, acm);
 
-	usb_get_intf(control_interface);
 	tty_dev = tty_port_register_device(&acm->port, acm_tty_driver, minor,
 			&control_interface->dev);
 	if (IS_ERR(tty_dev)) {