The writer of a patch is the copyright holder of that patch, as a result you cannot legally distribute your code with the patch applied unless you have a valid

The writer of a patch is the copyright holder of that patch, as a result you cannot legally distribute your code with the patch applied unless you have a valid license from the patch writer (Because part of the code is copyrighted by the patch writer, who has exclusive rights to distribution and reproduction). If the patch is submitted under the BSD/GPL/MIT license or similar, you are fine. All of those explicitly grant anyone that complies with those licenses to redistribute the patch code (and thus the patched project), with the usual restriction that your license is compatible and that said copyright notice and author names must be reproduced in the resulting entity. Normally you'd maintain an AUTHORS/CONTRIBUTORS files listing everyone's name in addition to the license files. There's no real hard and fast rule for this, though. Keeping the names in the contributed files would also work, for example. The situation is somewhat murky if the patch writer specifies no license. In this case you are technically not allowed to redistribute the patched code. If the codebase is on github and licensed under some open source license you could (try to) argue in court that that implies the patch is submitted under the same license as the original code, but whether that defense works is up to the judge.