Bruce Perens issues an advisory regarding the GRSecurity copyright issue:
https://perens.com/blog/2017/06/28/warning-grsecurity-potential-contributory-infringement-risk-for-customers/
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Warning: Grsecurity: Potential contributory infringement and breach of contract risk for customers

It\u2019s my strong opinion that your company should avoid the Grsecurity product sold at grsecurity.net because it presents a contributory infringement and breach of contract risk.

Grsecurity is a patch for the Linux kernel which, it is claimed, improves its security. It is a derivative work of the Linux kernel which touches the kernel internals in many different places. It is inseparable from Linux and can not work without it. it would fail a fair-use test (obviously, ask offline if you don\u2019t understand). Because of its strongly derivative nature of the kernel, it must be under the GPL version 2 license, or a license compatible with the GPL and with terms no more restrictive than the GPL. Earlier versions were distributed under GPL version 2.

Currently, Grsecurity is a commercial product and is distributed only to paying customers. My understanding from several reliable sources is that customers are verbally or otherwise warned that if they redistribute the Grsecurity patch, as would be their right under the GPL, that they will be assessed a penalty: they will no longer be allowed to be customers, and will not be granted access to any further versions of Grsecurity. GPL version 2 section 6 explicitly prohibits the addition of terms such as this redistribution prohibition.

By operating under their policy of terminating customer relations upon distribution of their GPL-licensed software, Open Source Security Inc., the owner of Grsecurity, creates an expectation that the customer\u2019s business will be damaged by losing access to support and later versions of the product, if that customer exercises their re-distribution right under the GPL license. This is tantamount to the addition of a term to the GPL prohibiting distribution or creating a penalty for distribution. GPL section 6 specifically prohibits any addition of terms. Thus, the GPL license, which allows Grsecurity to create its derivative work of the Linux kernel, terminates, and the copyright of the Linux Kernel is infringed. The contract from the Linux kernel developers to both Grsecurity and the customer which is inherent in the GPL is breached.

As a customer, it\u2019s my opinion that you would be subject to both contributory infringement and breach of contract by employing this product in conjunction with the Linux kernel under the no-redistribution policy currently employed by Grsecurity.

I have previously endorsed a company that distributes enhanced versions of GPL software to paying customers, but that company operated differently (and in a way that I would recommend to Grsecurity). They did not make any threat to customers regarding redistribution. They publicly distributed their commercial version within 9 months to one year after its customer-only distribution.