Re: KASAN: slab-out-of-bounds Read in usb_reset_and_verify_device

[Alan Stern]

On Tue, 3 Sep 2019, syzbot wrote:

> Hello,
> 
> syzbot has tested the proposed patch but the reproducer still triggered  
> crash:
> KASAN: slab-out-of-bounds Read in usb_reset_and_verify_device
> 
> usb 4-1: Using ep0 maxpacket: 16
> usb 4-1: Old BOS ffff8881d516b780  Len 0xa8
> usb 4-1: New BOS ffff8881d5dd6d20  Len 0xa8
> ==================================================================
> BUG: KASAN: slab-out-of-bounds in memcmp+0xa6/0xb0 lib/string.c:904
> Read of size 1 at addr ffff8881d5dd6db6 by task kworker/0:1/12

More debugging.  If my guess is right, this is pretty malicious...

Alan Stern

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

 drivers/usb/core/config.c |    2 ++
 drivers/usb/core/hub.c    |    7 +++++++
 2 files changed, 9 insertions(+)

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 %px  Len 0x%x\n",
+			bos, le16_to_cpu(bos->desc->wTotalLength));
+	if (udev->bos)
+		dev_info(&udev->dev, "New BOS %px  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");
Index: usb-devel/drivers/usb/core/config.c
===================================================================
--- usb-devel.orig/drivers/usb/core/config.c
+++ usb-devel/drivers/usb/core/config.c
@@ -966,6 +966,8 @@ int usb_get_bos_descriptor(struct usb_de
 			ret = -ENOMSG;
 		goto err;
 	}
+	dev_info(ddev, "BOS total length %d, descriptor %d\n", total_len,
+		le16_to_cpu(dev->bos->desc->wTotalLength));
 	total_len -= length;
 
 	for (i = 0; i < num; i++) {