CDC-NCM: avoid overflow in sanity checking

A broken device may give an extreme offset like 0xFFF0
and a reasonable length for a fragment. In the sanity
check as formulated now, this will create an integer
overflow, defeating the sanity check. Both offset
and offset + len need to be checked in such a manner
that no overflow can occur.
And those quantities should be unsigned.

Signed-off-by: Oliver Neukum <oneukum@suse.com>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/net/usb/cdc_ncm.c b/drivers/net/usb/cdc_ncm.c
index e303b52..15f91d6 100644 (file)
--- a/drivers/net/usb/cdc_ncm.c
+++ b/drivers/net/usb/cdc_ncm.c
@@ -1715,10 +1715,10 @@ int cdc_ncm_rx_fixup(struct usbnet *dev, struct sk_buff *skb_in)
 {
        struct sk_buff *skb;
        struct cdc_ncm_ctx *ctx = (struct cdc_ncm_ctx *)dev->data[0];
-       int len;
+       unsigned int len;
        int nframes;
        int x;
-       int offset;
+       unsigned int offset;
        union {
                struct usb_cdc_ncm_ndp16 *ndp16;
                struct usb_cdc_ncm_ndp32 *ndp32;
@@ -1790,8 +1790,8 @@ next_ndp:
                        break;
                }
 
-               /* sanity checking */
-               if (((offset + len) > skb_in->len) ||
+               /* sanity checking - watch out for integer wrap*/
+               if ((offset > skb_in->len) || (len > skb_in->len - offset) ||
                                (len > ctx->rx_max) || (len < ETH_HLEN)) {
                        netif_dbg(dev, rx_err, dev->net,
                                  "invalid frame detected (ignored) offset[%u]=%u, length=%u, skb=%p\n",