On Tue, Apr 26, 2022 at 09:54:18AM +0900, Tetsuo Handa wrote: > Since usb_register_dev() from imon_init_display() from imon_probe() holds > minor_rwsem while display_open() which holds driver_lock and ictx->lock is > called with minor_rwsem held from usb_open(), holding driver_lock or > ictx->lock when calling usb_register_dev() causes circular locking > dependency problem. > > Since usb_deregister_dev() from imon_disconnect() holds minor_rwsem while > display_open() which holds driver_lock is called with minor_rwsem held, > holding driver_lock when calling usb_deregister_dev() also causes circular > locking dependency problem. > > Sean Young explained that the problem is there are imon devices which have > two usb interfaces, even though it is one device. The probe and disconnect > function of both usb interfaces can run concurrently. > > Alan Stern responded that the driver and USB cores guarantee that when an > interface is probed, both the interface and its USB device are locked. > Ditto for when the disconnect callback gets run. So concurrent probing/ > disconnection of multiple interfaces on the same device is not possible. > > Therefore, simply remove redundant serialization. > > Link: https://syzkaller.appspot.com/bug?extid=c558267ad910fc494497 > Reported-by: syzbot <syzbot+c558267ad910fc494497@xxxxxxxxxxxxxxxxxxxxxxxxx> > Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx> > Cc: Sean Young <sean@xxxxxxxx> > Cc: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> Thanks, looks good! > --- > This patch might be OK for solving circular locking dependency problem. > But https://syzkaller.appspot.com/text?tag=CrashReport&x=1632f89f700000 says > free_imon_context() from imon_disconnect() can call kfree(ictx) before > display_close() is called, resulting in use-after-free problem. I guess that > we need to defer free_imon_context() using refcount till display_close() is > called. Fix as a separate patch or include into this patch? That is a separate issue, so that needs a separate patch. Sean > > drivers/media/rc/imon.c | 21 --------------------- > 1 file changed, 21 deletions(-) > > diff --git a/drivers/media/rc/imon.c b/drivers/media/rc/imon.c > index 54da6f60079b..e0e893d96cf3 100644 > --- a/drivers/media/rc/imon.c > +++ b/drivers/media/rc/imon.c > @@ -439,9 +439,6 @@ static struct usb_driver imon_driver = { > .id_table = imon_usb_id_table, > }; > > -/* to prevent races between open() and disconnect(), probing, etc */ > -static DEFINE_MUTEX(driver_lock); > - > /* Module bookkeeping bits */ > MODULE_AUTHOR(MOD_AUTHOR); > MODULE_DESCRIPTION(MOD_DESC); > @@ -499,9 +496,6 @@ static int display_open(struct inode *inode, struct file *file) > int subminor; > int retval = 0; > > - /* prevent races with disconnect */ > - mutex_lock(&driver_lock); > - > subminor = iminor(inode); > interface = usb_find_interface(&imon_driver, subminor); > if (!interface) { > @@ -534,7 +528,6 @@ static int display_open(struct inode *inode, struct file *file) > mutex_unlock(&ictx->lock); > > exit: > - mutex_unlock(&driver_lock); > return retval; > } > > @@ -2416,9 +2409,6 @@ static int imon_probe(struct usb_interface *interface, > dev_dbg(dev, "%s: found iMON device (%04x:%04x, intf%d)\n", > __func__, vendor, product, ifnum); > > - /* prevent races probing devices w/multiple interfaces */ > - mutex_lock(&driver_lock); > - > first_if = usb_ifnum_to_if(usbdev, 0); > if (!first_if) { > ret = -ENODEV; > @@ -2456,8 +2446,6 @@ static int imon_probe(struct usb_interface *interface, > usb_set_intfdata(interface, ictx); > > if (ifnum == 0) { > - mutex_lock(&ictx->lock); > - > if (product == 0xffdc && ictx->rf_device) { > sysfs_err = sysfs_create_group(&interface->dev.kobj, > &imon_rf_attr_group); > @@ -2468,21 +2456,17 @@ static int imon_probe(struct usb_interface *interface, > > if (ictx->display_supported) > imon_init_display(ictx, interface); > - > - mutex_unlock(&ictx->lock); > } > > dev_info(dev, "iMON device (%04x:%04x, intf%d) on usb<%d:%d> initialized\n", > vendor, product, ifnum, > usbdev->bus->busnum, usbdev->devnum); > > - mutex_unlock(&driver_lock); > usb_put_dev(usbdev); > > return 0; > > fail: > - mutex_unlock(&driver_lock); > usb_put_dev(usbdev); > dev_err(dev, "unable to register, err %d\n", ret); > > @@ -2498,9 +2482,6 @@ static void imon_disconnect(struct usb_interface *interface) > struct device *dev; > int ifnum; > > - /* prevent races with multi-interface device probing and display_open */ > - mutex_lock(&driver_lock); > - > ictx = usb_get_intfdata(interface); > dev = ictx->dev; > ifnum = interface->cur_altsetting->desc.bInterfaceNumber; > @@ -2545,8 +2526,6 @@ static void imon_disconnect(struct usb_interface *interface) > if (!ictx->dev_present_intf0 && !ictx->dev_present_intf1) > free_imon_context(ictx); > > - mutex_unlock(&driver_lock); > - > dev_dbg(dev, "%s: iMON device (intf%d) disconnected\n", > __func__, ifnum); > } > -- > 2.34.1 >
