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

commit 1c0edc3633b56000e18d82fc241e3995ca18a69e upstream.

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.

Reported-by: Andrey Konovalov <andreyknvl@google.com>
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Tested-by: Andrey Konovalov <andreyknvl@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
[sw0312.kim: cherry-pick from linux-3.16.y to fix usb issue related with CVE-2017-16531]
Signed-off-by: Seung-Woo Kim <sw0312.kim@samsung.com>
Change-Id: I85edcdcda17564d1c2e92e6980d27b34eacb5d4b

diff --git a/drivers/usb/core/config.c b/drivers/usb/core/config.c
index 6b3ca72..98a8750 100644 (file)
--- a/drivers/usb/core/config.c
+++ b/drivers/usb/core/config.c
@@ -828,10 +828,12 @@ 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) {