Re: WARNING in usb_submit_urb

[Alan Stern]

On Tue, 7 Nov 2017, Greg KH wrote:

> On Tue, Nov 07, 2017 at 08:11:13AM -0800, syzbot wrote:
> > Hello,
> > 
> > syzkaller hit the following crash on
> > 36ef71cae353f88fd6e095e2aaa3e5953af1685d
> > git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/master
> > compiler: gcc (GCC) 7.1.1 20170620
> > .config is attached
> > Raw console output is attached.
> > C reproducer is attached
> > syzkaller reproducer is attached. See https://goo.gl/kgGztJ
> > for information about syzkaller reproducers
> 
> This is not a crash, you are doing a panic-on-warning, and you send
> invalid data to the kernel and it warned about it properly and kept on
> working :)
> 
> Perhaps maybe not a full WARN_ON() is to be done here?

I don't understand how this could have happened.  The raw log explains 
the problem:

> [   15.138822] usb usb1: BOGUS urb flags, 2 --> 0
> [   15.139498] ------------[ cut here ]------------
> [   15.139955] WARNING: CPU: 3 PID: 2986 at drivers/usb/core/urb.c:498 usb_submit_urb+0xeb9/0x10f0
...
> [   15.150280] RIP: 0010:usb_submit_urb+0xeb9/0x10f0
...
> [   15.155166]  proc_do_submiturb+0x1f53/0x3860

The "2 --> 0" means that proc_do_submiturb() tried to submit a control
URB (2 = PIPE_CONTROL) to an isochronous endpoint (0 = PIPE_ISOCHRONOUS).
But right near the start of the routine we have:

	switch (uurb->type) {
	case USBDEVFS_URB_TYPE_CONTROL:
		if (!usb_endpoint_xfer_control(&ep->desc))
			return -EINVAL;

So how was the warning triggered?

Alan Stern