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Date:   Tue, 29 Dec 2020 11:33:37 -0500
From:   Alan Stern <stern@...land.harvard.edu>
To:     syzbot <syzbot+5925509f78293baa7331@...kaller.appspotmail.com>
Cc:     andreyknvl@...il.com, andreyknvl@...gle.com, balbi@...nel.org,
        gregkh@...uxfoundation.org, gustavoars@...nel.org,
        linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
        syzkaller-bugs@...glegroups.com
Subject: Re: UBSAN: shift-out-of-bounds in dummy_hub_control

On Fri, Dec 25, 2020 at 12:05:22PM -0800, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    e37b12e4 Merge tag 'for-linus-5.11-ofs1' of git://git.kern..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=17429937500000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=98408202fed1f636
> dashboard link: https://syzkaller.appspot.com/bug?extid=5925509f78293baa7331
> compiler:       gcc (GCC) 10.1.0-syz 20200507
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1781fc5b500000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=157cd123500000
> 
> The issue was bisected to:
> 
> commit 8442b02bf3c6770e0d7e7ea17be36c30e95987b6
> Author: Andrey Konovalov <andreyknvl@...gle.com>
> Date:   Mon Oct 21 14:20:58 2019 +0000
> 
>     USB: dummy-hcd: increase max number of devices to 32
> 
> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=1631d0db500000
> final oops:     https://syzkaller.appspot.com/x/report.txt?x=1531d0db500000
> console output: https://syzkaller.appspot.com/x/log.txt?x=1131d0db500000
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+5925509f78293baa7331@...kaller.appspotmail.com
> Fixes: 8442b02bf3c6 ("USB: dummy-hcd: increase max number of devices to 32")
> 
> ================================================================================
> UBSAN: shift-out-of-bounds in drivers/usb/gadget/udc/dummy_hcd.c:2293:33
> shift exponent 257 is too large for 32-bit type 'int'
> CPU: 0 PID: 8526 Comm: syz-executor949 Not tainted 5.10.0-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> Call Trace:
>  __dump_stack lib/dump_stack.c:79 [inline]
>  dump_stack+0x107/0x163 lib/dump_stack.c:120
>  ubsan_epilogue+0xb/0x5a lib/ubsan.c:148
>  __ubsan_handle_shift_out_of_bounds.cold+0xb1/0x181 lib/ubsan.c:395
>  dummy_hub_control.cold+0x1a/0xbc drivers/usb/gadget/udc/dummy_hcd.c:2293
>  rh_call_control drivers/usb/core/hcd.c:683 [inline]
>  rh_urb_enqueue drivers/usb/core/hcd.c:841 [inline]
>  usb_hcd_submit_urb+0xcaa/0x22d0 drivers/usb/core/hcd.c:1544
>  usb_submit_urb+0x6e4/0x1560 drivers/usb/core/urb.c:585
>  usb_start_wait_urb+0x101/0x4c0 drivers/usb/core/message.c:58
>  usb_internal_control_msg drivers/usb/core/message.c:102 [inline]
>  usb_control_msg+0x31c/0x4a0 drivers/usb/core/message.c:153
>  do_proc_control+0x4cb/0x9c0 drivers/usb/core/devio.c:1165
>  proc_control drivers/usb/core/devio.c:1191 [inline]
>  usbdev_do_ioctl drivers/usb/core/devio.c:2535 [inline]
>  usbdev_ioctl+0x12c1/0x3b20 drivers/usb/core/devio.c:2708
>  vfs_ioctl fs/ioctl.c:48 [inline]
>  __do_sys_ioctl fs/ioctl.c:753 [inline]
>  __se_sys_ioctl fs/ioctl.c:739 [inline]
>  __x64_sys_ioctl+0x193/0x200 fs/ioctl.c:739
>  do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
>  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> RIP: 0033:0x443f29
> Code: 18 89 d0 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 0f 83 fb d7 fb ff c3 66 2e 0f 1f 84 00 00 00 00
> RSP: 002b:00007ffc10df4328 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
> RAX: ffffffffffffffda RBX: 00000000004002e0 RCX: 0000000000443f29
> RDX: 0000000020000000 RSI: 00000000c0185500 RDI: 0000000000000003
> RBP: 00000000006ce018 R08: 0000000000000000 R09: 00000000004002e0
> R10: 000000000000000f R11: 0000000000000246 R12: 0000000000401bb0
> R13: 0000000000401c40 R14: 0000000000000000 R15: 0000000000000000
> ================================================================================

The cause is pretty obvious.  dummy-hcd assumes that requests sent to 
the root hub are always valid, which isn't always true when they come 
from userspace.

Alan Stern

#syz test: upstream e37b12e4

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:

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