Today the final version of the GPL version 3 was released. This is interesting from many perspectives, and one of them is Snort licensing. Much has been written about Snort and the GPL lately, but that was all about new license language introduced with Snort 3.0 alpha and not about the currently maintained and developed 2.6 and 2.7 branches. When I’m talking about Snort here and now, I mean those versions prior to 3.0.

Snort, like many other OSS projects (including my own Vuurmuur and Modsec2Sguil) comes with many files (but not all) that are distributed with the following lines in the copyright notice:

** This program is free software; you can redistribute it and/or modify
** it under the terms of the GNU General Public License as published by
** the Free Software Foundation; either version 2 of the License, or
** (at your option) any later version.

What it says, is that the GPLv2 license applies to this file, but that if there is a newer GPL license available (GPLv3 in this case), you may choose to ‘redistribute it and/or modify it’ under that later version. So it appears that this means that the files in Snort that contain this header can be distributed under the GPLv3 as well.

SourceFire however, disagrees. Martin Roesch wrote on Snort.org that SourceFire has chosen not to do the transition to the GPLv3 yet. He points to a page on the snort.org site where it is explained why SourceFire thinks that despite the ‘(at your option) any later version’ line, only the GPLv2 applies to Snort.

The reasoning is rather simple, Snort is governed by the GPLv2 because it is governed by the GPLv2. Here is how SourceFire said it:

“SNORT is an open source project that is governed exclusively by the GPL V2 and any third party desiring to use, modify or distribute SNORT must do so by strictly following the terms and conditions of GPL V2. Anyone using, modifying or distributing SNORT does not have the option to choose to use, modify or distribute SNORT under any revised or new version of the GPL, including without limitation, the GNU General Public License Version 3.” (source)

I think this is an impossible position. For years the Snort source code has been distributed leaving the option to developers to pick a new version of the GPL when it would become available. But now that this time has come, they are coming back to that. Here is what they say:

“For ease of reference, the comparable notice that is used with SNORT (contained in the ‘README’ file) is as follows:

“This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License Version 2 as published by the Free Software Foundation. You may not use, modify or distribute this program under any other version of the GNU General Public License.”” (source)

Note however, that future versions of Snort may hold this notice, but currently released code does not. Apparently, SourceFire has no trust in their own explanation of the ‘(at your option) any later version’ line, so they are going to remove it altogether.

In my opinion this is effectively a licensing change. It changes from GPLv2+ to GPLv2. This has a couple of implications. First of all, all code already out there is licensed as it is. The language in the source files is clear. Second of all, while SourceFire has certainly written the vast majority of code, not all code in Snort is copyrighted by them. Copyright of the Snort_inline project was not transferred to SourceFire when they incorporated our inline patch in 2.3.0RC1. There may be other contributions by others without copyright transfer.

Many projects have chosen to change the licensing language long ago to remove the ‘(at your option) any later version’ line. SourceFire hasn’t done this. It is my believe that by deliberately spreading the code with this clause for many years, SourceFire is allowing anyone to ‘redistribute it and/or modify’ the affected source files under the GPL version 3.

Disclaimer: this is my personal opinion, not (necessarily) the opinion of other Snort_inline developers.