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.

Reported-by: Andrey Konovalov <andreyknvl@google.com>
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Tested-by: Andrey Konovalov <andreyknvl@google.com>
CC: <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/usb/core/config.c b/drivers/usb/core/config.c
index 68b54bd88d1eb009eddac3132402717a9c25f580..883549ee946cb5e206623bfc79d199620078a6bb 100644 (file)
--- a/drivers/usb/core/config.c
+++ b/drivers/usb/core/config.c
@@ -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) {