On Fri, Jun 03, 2022 at 05:52:38PM +0200, Greg KH wrote: > On Fri, Jun 03, 2022 at 11:42:19AM -0400, Alan Stern wrote: > > 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()? > > But how can that really fail on a real system? > > Is this just due to error-injection stuff? If so, I'm really loath to > rework the world for something that can never happen in real life. > > Or is this a real syzbot-found-with-reproducer issue? Aren't there quite a few reasons why device_add() might fail? (Although most of them probably are memory allocation errors...) Basically, you have to make up your mind. If a function can fail, you should be prepared to handle the failure. If it can't fail, there's no point in even checking the return code. Alan Stern
