patch "USB: core: fix out-of-bounds access bug in usb_get_bos_descriptor()" added to usb-linus

This is a note to let you know that I've just added the patch titled

USB: core: fix out-of-bounds access bug in usb_get_bos_descriptor()

to my usb git tree which can be found at
git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb.git
in the usb-linus branch.

The patch will show up in the next release of the linux-next tree (usually sometime within the next 24 hours during the week.)

The patch will hopefully also be merged in Linus's tree for the next -rc kernel release.

If you have any questions about this process, please let me know.

From: Alan Stern <[email protected]>
Date: Wed, 18 Oct 2017 12:49:38 -0400
Subject: USB: core: fix out-of-bounds access bug in usb_get_bos_descriptor()

Andrey used the syzkaller fuzzer to find an out-of-bounds memory access in usb_get_bos_descriptor(). The code wasn't checking that the next usb_dev_cap_header structure could fit into the remaining buffer space.

This patch fixes the error and also reduces the bNumDeviceCaps field in the header to match the actual number of capabilities found, in cases where there are fewer than expected.

---
 drivers/usb/core/config.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

index 68b54bd88d1e..883549ee946c 100644
@@ -960,10 +960,12 @@ int usb_get_bos_descriptor(struct usb_device *dev)
 	for (i = 0; i < num; i++) {
 		buffer += length;
 		cap = (struct usb_dev_cap_header *)buffer;
-		length = cap->bLength;
 
-		if (total_len < length)
+		if (total_len < sizeof(*cap) || total_len < cap->bLength) {
+			dev->bos->desc->bNumDeviceCaps = i;
 			break;
+		}
+		length = cap->bLength;
 		total_len -= length;
 
 		if (cap->bDescriptorType != USB_DT_DEVICE_CAPABILITY) {

2.14.2