The GPLv2 has an implicit patent pledge: 6. Each time you redistribute the Program (or any work based on the Program), the recipient automatically receives a l

The GPLv2 has an implicit patent pledge: 6. Each time you redistribute the Program (or any work based on the Program), the recipient automatically receives a license from the original licensor to copy, distribute or modify the Program subject to these terms and conditions. You may not impose any further restrictions on the recipients' exercise of the rights granted herein. You are not responsible for enforcing compliance by third parties to this License. In particular: You may not impose any further restrictions on the recipients' exercise of the rights granted herein. Of course, whether it is enforceable may be a different question (IANAL).