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Tue, 08 Sep 2026 17:48:06 -0700 (PDT) From: Ivy Lopez To: gregkh@linuxfoundation.org, linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org Cc: oneukum@suse.com, kees@kernel.org, Ivy Lopez , syzbot+023b30ebfe0dc4bcfafe@syzkaller.appspotmail.com Subject: [PATCH] usb: mdc800: fix circular locking dependency in probe/open Date: Tue, 8 Sep 2026 18:48:02 -0600 Message-ID: <20260909004802.233380-1-skunkolee@gmail.com> X-Mailer: git-send-email 2.55.0 Precedence: bulk X-Mailing-List: linux-usb@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit mdc800_usb_probe() acquired mdc800->io_lock before calling usb_register_dev(), which internally takes minor_rwsem. Meanwhile mdc800_device_open() is called through usb_open() with minor_rwsem already held, and then tries to acquire io_lock, producing an AB-BA lock inversion: probe: io_lock -> minor_rwsem (via usb_register_dev) open: minor_rwsem -> io_lock Until usb_register_dev() succeeds and creates the device node, no concurrent open can happen, so io_lock provides no protection during probe before that point. Move usb_register_dev() to the end of the probe function, after all URB and state setup, and drop io_lock entirely from probe, eliminating the inversion. Reported-by: syzbot+023b30ebfe0dc4bcfafe@syzkaller.appspotmail.com Signed-off-by: Ivy Lopez --- drivers/usb/image/mdc800.c | 15 +++++---------- 1 file changed, 5 insertions(+), 10 deletions(-) diff --git a/drivers/usb/image/mdc800.c b/drivers/usb/image/mdc800.c index ca287b770e8c..976f751886f9 100644 --- a/drivers/usb/image/mdc800.c +++ b/drivers/usb/image/mdc800.c @@ -480,15 +480,6 @@ static int mdc800_usb_probe (struct usb_interface *intf, dev_info(&intf->dev, "Found Mustek MDC800 on USB.\n"); - mutex_lock(&mdc800->io_lock); - - retval = usb_register_dev(intf, &mdc800_class); - if (retval) { - dev_err(&intf->dev, "Not able to get a minor for this device.\n"); - mutex_unlock(&mdc800->io_lock); - return -ENODEV; - } - mdc800->dev=dev; mdc800->open=0; @@ -526,7 +517,11 @@ static int mdc800_usb_probe (struct usb_interface *intf, mdc800->state=READY; - mutex_unlock(&mdc800->io_lock); + retval = usb_register_dev(intf, &mdc800_class); + if (retval) { + dev_err(&intf->dev, "Not able to get a minor for this device.\n"); + return -ENODEV; + } usb_set_intfdata(intf, mdc800); return 0; -- 2.55.0