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Date:   Tue, 7 Jan 2020 15:43:50 -0500 (EST)
From:   Alan Stern <stern@rowland.harvard.edu>
To:     syzbot <syzbot+10e5f68920f13587ab12@syzkaller.appspotmail.com>
cc:     andreyknvl@google.com, <gregkh@linuxfoundation.org>,
        <gustavo@embeddedor.com>, <ingrassia@epigenesys.com>,
        <linux-kernel@vger.kernel.org>, <linux-usb@vger.kernel.org>,
        <syzkaller-bugs@googlegroups.com>
Subject: Re: WARNING in usbhid_raw_request/usb_submit_urb (2)
In-Reply-To: <0000000000003a83be059b91c6e4@google.com>
Message-ID: <Pine.LNX.4.44L0.2001071541020.1567-100000@iolanthe.rowland.org>
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On Tue, 7 Jan 2020, syzbot wrote:

> Hello,
> 
> syzbot has tested the proposed patch and the reproducer did not trigger  
> crash:
> 
> Reported-and-tested-by:  
> syzbot+10e5f68920f13587ab12@syzkaller.appspotmail.com
> 
> Tested on:
> 
> commit:         ecdf2214 usb: gadget: add raw-gadget interface
> git tree:       https://github.com/google/kasan.git
> kernel config:  https://syzkaller.appspot.com/x/.config?x=b06a019075333661
> dashboard link: https://syzkaller.appspot.com/bug?extid=10e5f68920f13587ab12
> compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
> patch:          https://syzkaller.appspot.com/x/patch.diff?x=11543656e00000
> 
> Note: testing is done by a robot and is best-effort only.

Not very informative. I wonder just how elusive this race is.  The
patch below doesn't change anything; let's see what happens.

Alan Stern

#syz test: https://github.com/google/kasan.git ecdf2214

Index: usb-devel/drivers/usb/core/urb.c
===================================================================
--- usb-devel.orig/drivers/usb/core/urb.c
+++ usb-devel/drivers/usb/core/urb.c
@@ -205,7 +205,7 @@ int usb_urb_ep_type_check(const struct u
 
 	ep = usb_pipe_endpoint(urb->dev, urb->pipe);
 	if (!ep)
-		return -EINVAL;
+		return -EINVAL;
 	if (usb_pipetype(urb->pipe) != pipetypes[usb_endpoint_type(&ep->desc)])
 		return -EINVAL;
 	return 0;