On Fri, Jun 03, 2022 at 02:04:04PM +0300, Andy Shevchenko wrote: > On Fri, Jun 03, 2022 at 03:02:07AM -0700, syzbot wrote: > > syzbot has bisected this issue to: > > > > commit a9c4cf299f5f79d5016c8a9646fa1fc49381a8c1 > > Author: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx> > > Date: Fri Jun 18 13:41:27 2021 +0000 > > > > ACPI: sysfs: Use __ATTR_RO() and __ATTR_RW() macros > > Hmm... It's not obvious at all how this change can alter the behaviour so > drastically. device_add() is called from USB core with intf->dev.name == NULL > by some reason. A-ha, seems like fault injector, which looks like > > dev_set_name(&intf->dev, "%d-%s:%d.%d", dev->bus->busnum, > dev->devpath, configuration, ifnum); > > missed the return code check. > > But I'm not familiar with that code at all, adding Linux USB ML and Alan. I can't see any connection between this bug and acpi/sysfs.c. Is it a bad bisection? It looks like you're right about dev_set_name() failing. In fact, the kernel appears to be littered with calls to that routine which do not check the return code (the entire subtree below drivers/usb/ contains only _one_ call that does check the return code!). The function doesn't have any __must_check annotation, and its kerneldoc doesn't mention the return code or the possibility of a failure. Apparently the assumption is that if dev_set_name() fails then device_add() later on will also fail, and the problem will be detected then. So now what should happen when device_add() for an interface fails in usb_set_configuration()? I guess the interface should be deleted; otherwise we have the possibility that people might still try to access it via usbfs, as in the syzbot test run. Same goes for the of_device_is_available() check. Fixing that will be a little painful. Right now there are plenty of places in the USB core that aren't prepared to cope with a non-existent interface. Alan Stern
