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Date:   Tue, 3 Sep 2019 15:03:45 -0400 (EDT)
From:   Alan Stern <stern@rowland.harvard.edu>
To:     syzbot <syzbot+35f4d916c623118d576e@syzkaller.appspotmail.com>
cc:     Thinh.Nguyen@synopsys.com, <andreyknvl@google.com>,
        <dianders@chromium.org>, <gregkh@linuxfoundation.org>,
        <jflat@chromium.org>, <kai.heng.feng@canonical.com>,
        <linux-kernel@vger.kernel.org>, <linux-usb@vger.kernel.org>,
        <malat@debian.org>, <mathias.nyman@linux.intel.com>,
        <nsaenzjulienne@suse.de>, <syzkaller-bugs@googlegroups.com>
Subject: Re: KASAN: slab-out-of-bounds Read in usb_reset_and_verify_device
In-Reply-To: <000000000000318cba0591a4f143@google.com>
Message-ID: <Pine.LNX.4.44L0.1909031501550.1859-100000@iolanthe.rowland.org>
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On Tue, 3 Sep 2019, syzbot wrote:

> Hello,
> 
> syzbot found the following crash on:
> 
> HEAD commit:    eea39f24 usb-fuzzer: main usb gadget fuzzer driver
> git tree:       https://github.com/google/kasan.git usb-fuzzer
> console output: https://syzkaller.appspot.com/x/log.txt?x=174761b6600000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=d0c62209eedfd54e
> dashboard link: https://syzkaller.appspot.com/bug?extid=35f4d916c623118d576e
> compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1706275a600000
> 
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+35f4d916c623118d576e@syzkaller.appspotmail.com
> 
> ==================================================================
> BUG: KASAN: slab-out-of-bounds in memcmp+0xa6/0xb0 lib/string.c:904
> Read of size 1 at addr ffff8881d175bed6 by task kworker/0:3/2746
> 
> CPU: 0 PID: 2746 Comm: kworker/0:3 Not tainted 5.3.0-rc5+ #28
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
> Google 01/01/2011
> Workqueue: usb_hub_wq hub_event
> Call Trace:
>   __dump_stack lib/dump_stack.c:77 [inline]
>   dump_stack+0xca/0x13e lib/dump_stack.c:113
>   print_address_description+0x6a/0x32c mm/kasan/report.c:351
>   __kasan_report.cold+0x1a/0x33 mm/kasan/report.c:482
>   kasan_report+0xe/0x12 mm/kasan/common.c:612
>   memcmp+0xa6/0xb0 lib/string.c:904
>   memcmp include/linux/string.h:400 [inline]
>   descriptors_changed drivers/usb/core/hub.c:5579 [inline]
>   usb_reset_and_verify_device+0x564/0x1300 drivers/usb/core/hub.c:5729

Diagnostic patch.

#syz test: https://github.com/google/kasan.git eea39f24

Index: usb-devel/drivers/usb/core/hub.c
===================================================================
--- usb-devel.orig/drivers/usb/core/hub.c
+++ usb-devel/drivers/usb/core/hub.c
@@ -5721,6 +5721,13 @@ static int usb_reset_and_verify_device(s
 	if (ret < 0)
 		goto re_enumerate;
 
+	if (bos)
+		dev_info(&udev->dev, "Old BOS %p  Len 0x%x\n",
+			bos, le16_to_cpu(bos->desc->wTotalLength));
+	if (udev->bos)
+		dev_info(&udev->dev, "New BOS %p  Len 0x%x\n",
+			udev->bos, le16_to_cpu(udev->bos->desc->wTotalLength));
+
 	/* Device might have changed firmware (DFU or similar) */
 	if (descriptors_changed(udev, &descriptor, bos)) {
 		dev_info(&udev->dev, "device firmware changed\n");