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From:   Schspa Shi <schspa@gmail.com>
To:     stern@rowland.harvard.edu
Cc:     Julia.Lawall@inria.fr, andreyknvl@gmail.com, balbi@kernel.org,
        gregkh@linuxfoundation.org, jannh@google.com,
        jj251510319013@gmail.com, linux-kernel@vger.kernel.org,
        linux-usb@vger.kernel.org, schspa@gmail.com,
        syzbot+dc7c3ca638e773db07f6@syzkaller.appspotmail.com
Subject: [PATCH v3] usb: gadget: fix race when gadget driver register via ioctl
Date:   Sun,  8 May 2022 23:02:47 +0800
Message-Id: <20220508150247.38204-1-schspa@gmail.com>
In-Reply-To: <YnfVEcOWO63uIGs5@rowland.harvard.edu>
References: <YnfVEcOWO63uIGs5@rowland.harvard.edu>
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The usb_gadget_register_driver can be called multi time by to
threads via USB_RAW_IOCTL_RUN ioctl syscall, which will lead
to multiple registrations.

Call trace:
  driver_register+0x220/0x3a0 drivers/base/driver.c:171
  usb_gadget_register_driver_owner+0xfb/0x1e0
    drivers/usb/gadget/udc/core.c:1546
  raw_ioctl_run drivers/usb/gadget/legacy/raw_gadget.c:513 [inline]
  raw_ioctl+0x1883/0x2730 drivers/usb/gadget/legacy/raw_gadget.c:1220
  ioctl USB_RAW_IOCTL_RUN

This routine allows two processes to register the same driver instance
via ioctl syscall. which lead to a race condition.

Please refer to the following scenarios.

           T1                                  T2
------------------------------------------------------------------
usb_gadget_register_driver_owner
  driver_register                    driver_register
    driver_find                       driver_find
    bus_add_driver                    bus_add_driver
      priv alloced                     <context switch>
      drv->p = priv;
      <schedule out>
      kobject_init_and_add // refcount = 1;
   //couldn't find an available UDC or it's busy
   <context switch>
                                       priv alloced
                                       drv->priv = priv;
                                       kobject_init_and_add
                                         ---> refcount = 1 <------
                                       // register success
                                       <context switch>
===================== another ioctl/process ======================
                                      driver_register
                                       driver_find
                                        k = kset_find_obj()
                                         ---> refcount = 2 <------
                                        <context out>
   driver_unregister
   // drv->p become T2's priv
   ---> refcount = 1 <------
   <context switch>
                                        kobject_put(k)
                                         ---> refcount = 0 <------
                                        return priv->driver;
                                        --------UAF here----------

There will be UAF in this scenario.

We can fix it by adding a new STATE_DEV_REGISTERING device state to
avoid double register.

Reported-by: syzbot+dc7c3ca638e773db07f6@syzkaller.appspotmail.com
Link: https://lore.kernel.org/all/000000000000e66c2805de55b15a@google.com/

Signed-off-by: Schspa Shi <schspa@gmail.com>

---

Changelog:
v1 -> v2:
        - Add a STATE_DEV_REGISTERING as Alan Stern suggested.
v2 -> v3:
        - Adjust STATE_DEV_REGISTERING position to reflect the actual
          order in which the states occur.
        - Add the fault scenarios to comments.
---
 drivers/usb/gadget/legacy/raw_gadget.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/usb/gadget/legacy/raw_gadget.c b/drivers/usb/gadget/legacy/raw_gadget.c
index b3be8db1ff63..241740024c50 100644
--- a/drivers/usb/gadget/legacy/raw_gadget.c
+++ b/drivers/usb/gadget/legacy/raw_gadget.c
@@ -145,6 +145,7 @@ enum dev_state {
 	STATE_DEV_INVALID = 0,
 	STATE_DEV_OPENED,
 	STATE_DEV_INITIALIZED,
+	STATE_DEV_REGISTERING,
 	STATE_DEV_RUNNING,
 	STATE_DEV_CLOSED,
 	STATE_DEV_FAILED
@@ -508,6 +509,7 @@ static int raw_ioctl_run(struct raw_dev *dev, unsigned long value)
 		ret = -EINVAL;
 		goto out_unlock;
 	}
+	dev->state = STATE_DEV_REGISTERING;
 	spin_unlock_irqrestore(&dev->lock, flags);
 
 	ret = usb_gadget_register_driver(&dev->driver);
-- 
2.24.3 (Apple Git-128)