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Date:   Tue, 16 Apr 2019 17:14:38 -0400 (EDT)
From:   Alan Stern <stern@rowland.harvard.edu>
To:     syzbot <syzbot+d919b0f29d7b5a4994b9@syzkaller.appspotmail.com>
cc:     andreyknvl@google.com, <gregkh@linuxfoundation.org>,
        <gustavo@embeddedor.com>, <linux-kernel@vger.kernel.org>,
        <linux-usb@vger.kernel.org>, <syzkaller-bugs@googlegroups.com>
Subject: Re: INFO: task hung in usb_kill_urb
In-Reply-To: <000000000000fb61d40586aa6a1e@google.com>
Message-ID: <Pine.LNX.4.44L0.1904161707210.1605-100000@iolanthe.rowland.org>
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Sender: linux-kernel-owner@vger.kernel.org
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On Tue, 16 Apr 2019, syzbot wrote:

> Hello,
> 
> syzbot has tested the proposed patch and the reproducer did not trigger  
> crash:

Slight fixup to the patch.  Unsupported speeds aren't necessarily 
bogus, and what matters is the actual speed rather than the max_speed.
Also, we want to be able to give back unlinked URBs even after a 
frame's total bandwidth has been exhausted.

Alan Stern

#syz test: https://github.com/google/kasan.git usb-fuzzer

--- a/drivers/usb/gadget/udc/dummy_hcd.c
+++ b/drivers/usb/gadget/udc/dummy_hcd.c
@@ -979,8 +979,18 @@ static int dummy_udc_start(struct usb_ga
 	struct dummy_hcd	*dum_hcd = gadget_to_dummy_hcd(g);
 	struct dummy		*dum = dum_hcd->dum;
 
-	if (driver->max_speed == USB_SPEED_UNKNOWN)
+	switch (g->speed) {
+	/* All the speeds we support */
+	case USB_SPEED_LOW:
+	case USB_SPEED_FULL:
+	case USB_SPEED_HIGH:
+	case USB_SPEED_SUPER:
+		break;
+	default:
+		dev_err(dummy_dev(dum_hcd), "Unsupported driver max speed %d\n",
+				driver->max_speed);
 		return -EINVAL;
+	}
 
 	/*
 	 * SLAVE side init ... the layer above hardware, which
@@ -1784,7 +1794,7 @@ static void dummy_timer(struct timer_lis
 		/* Bus speed is 500000 bytes/ms, so use a little less */
 		total = 490000;
 		break;
-	default:
+	default:	/* Can't happen */
 		dev_err(dummy_dev(dum_hcd), "bogus device speed\n");
 		return;
 	}
@@ -1828,7 +1838,7 @@ restart:
 
 		/* Used up this frame's bandwidth? */
 		if (total <= 0)
-			break;
+			continue;
 
 		/* find the gadget's ep for this request (if configured) */
 		address = usb_pipeendpoint (urb->pipe);