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From: Alan Stern <stern@rowland.harvard.edu>
To: Greg KH <greg@kroah.com>, Felipe Balbi <balbi@kernel.org>
Cc: gustavoars@kernel.org,
	USB mailing list <linux-usb@vger.kernel.org>,
	syzkaller-bugs@googlegroups.com
Subject: [PATCH] USB: Gadget: dummy-hcd: Fix shift-out-of-bounds bug
Date: Wed, 30 Dec 2020 11:20:44 -0500
Message-ID: <20201230162044.GA727759@rowland.harvard.edu> (raw)
In-Reply-To: <0000000000009f3cf405b79d5267@google.com>

The dummy-hcd driver was written under the assumption that all the
parameters in URBs sent to its root hub would be valid.  With URBs
sent from userspace via usbfs, that assumption can be violated.

In particular, the driver doesn't fully check the port-feature values
stored in the wValue entry of Clear-Port-Feature and Set-Port-Feature
requests.  Values that are too large can cause the driver to perform
an invalid left shift of more than 32 bits.  Ironically, two of those
left shifts are unnecessary, because they implement Set-Port-Feature
requests that hubs are not required to support, according to section
11.24.2.13 of the USB-2.0 spec.

This patch adds the appropriate checks for the port feature selector
values and removes the unnecessary feature settings.  It also rejects
requests to set the TEST feature or to set or clear the INDICATOR and
C_OVERCURRENT features, as none of these are relevant to dummy-hcd's
root-hub emulation.

Reported-and-tested-by: syzbot+5925509f78293baa7331@syzkaller.appspotmail.com
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
CC: <stable@vger.kernel.org>

---


[as1951]


 drivers/usb/gadget/udc/dummy_hcd.c |   35 +++++++++++++++++++++++------------
 1 file changed, 23 insertions(+), 12 deletions(-)

Index: usb-devel/drivers/usb/gadget/udc/dummy_hcd.c
===================================================================
--- usb-devel.orig/drivers/usb/gadget/udc/dummy_hcd.c
+++ usb-devel/drivers/usb/gadget/udc/dummy_hcd.c
@@ -2114,9 +2114,21 @@ static int dummy_hub_control(
 				dum_hcd->port_status &= ~USB_PORT_STAT_POWER;
 			set_link_state(dum_hcd);
 			break;
-		default:
+		case USB_PORT_FEAT_ENABLE:
+		case USB_PORT_FEAT_C_ENABLE:
+		case USB_PORT_FEAT_C_SUSPEND:
+			/* Not allowed for USB-3 */
+			if (hcd->speed == HCD_USB3)
+				goto error;
+			fallthrough;
+		case USB_PORT_FEAT_C_CONNECTION:
+		case USB_PORT_FEAT_C_RESET:
 			dum_hcd->port_status &= ~(1 << wValue);
 			set_link_state(dum_hcd);
+			break;
+		default:
+		/* Disallow INDICATOR and C_OVER_CURRENT */
+			goto error;
 		}
 		break;
 	case GetHubDescriptor:
@@ -2277,18 +2289,17 @@ static int dummy_hub_control(
 			 */
 			dum_hcd->re_timeout = jiffies + msecs_to_jiffies(50);
 			fallthrough;
+		case USB_PORT_FEAT_C_CONNECTION:
+		case USB_PORT_FEAT_C_RESET:
+		case USB_PORT_FEAT_C_ENABLE:
+		case USB_PORT_FEAT_C_SUSPEND:
+			/* Not allowed for USB-3, and ignored for USB-2 */
+			if (hcd->speed == HCD_USB3)
+				goto error;
+			break;
 		default:
-			if (hcd->speed == HCD_USB3) {
-				if ((dum_hcd->port_status &
-				     USB_SS_PORT_STAT_POWER) != 0) {
-					dum_hcd->port_status |= (1 << wValue);
-				}
-			} else
-				if ((dum_hcd->port_status &
-				     USB_PORT_STAT_POWER) != 0) {
-					dum_hcd->port_status |= (1 << wValue);
-				}
-			set_link_state(dum_hcd);
+		/* Disallow TEST, INDICATOR, and C_OVER_CURRENT */
+			goto error;
 		}
 		break;
 	case GetPortErrorCount:

      reply index

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-12-25 20:05 UBSAN: shift-out-of-bounds in dummy_hub_control syzbot
2020-12-29 16:33 ` Alan Stern
2020-12-29 16:33   ` syzbot
2020-12-29 16:43     ` Alan Stern
2020-12-29 17:00       ` syzbot
2020-12-30 16:20         ` Alan Stern [this message]

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