Staging: bcm: Fix an integer overflow in IOCTL_BCM_NVM_READ/WRITE

Variables stNVMReadWrite.uioffset and stNVMReadWrite.uiNumBytes
are chosen from userspace and can be very high. The sum of
these two digits would result in a small number. Therefore,
this patch verifies a negative number was not entered, and
reorganizes the equation to remove the integer overflow.
Signed-off-by: Kevin McKinney <klmckinney1@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/bcm/Bcmchar.c

@@ -1302,8 +1302,10 @@ static long bcm_char_ioctl(struct file *filp, UINT cmd, ULONG arg)
 		/*
 		 * Deny the access if the offset crosses the cal area limit.
 		 */
+		if (stNVMReadWrite.uiNumBytes > Adapter->uiNVMDSDSize)
+			return STATUS_FAILURE;
 
-		if ((stNVMReadWrite.uiOffset + stNVMReadWrite.uiNumBytes) > Adapter->uiNVMDSDSize) {
+		if (stNVMReadWrite.uiOffset > Adapter->uiNVMDSDSize - stNVMReadWrite.uiNumBytes) {
 			/* BCM_DEBUG_PRINT(Adapter,DBG_TYPE_PRINTK, 0, 0,"Can't allow access beyond NVM Size: 0x%x 0x%x\n", stNVMReadWrite.uiOffset, stNVMReadWrite.uiNumBytes); */
 			return STATUS_FAILURE;
 		}