Hello, Eric, Marco, all, This is JFYI and a follow-up message.
A further investigation was made to find out the Linux kernel commit which has introduced the flaw. It appeared that previous Linux kernel versions are vulnerable, down to v3.6-rc1. This fact was hidden by 'net.ipv4.tcp_fastopen' set to 0 by default, and now it is easier to notice since kernel v3.12 due to commit 0d41cca490 where the default was changed to 1. With 'net.ipv4.tcp_fastopen' set to 1, previous Linux kernels (including RHEL-7 ones) are also vulnerable. The bug is here since tcp-fastopen feature was introduced in kernel v3.6-rc1, the first commit when the reproducer starts to panic the kernel with net.ipv4.tcp_fastopen=1 set is cf60af03ca, which is a part of commit sequence 2100c8d2d9..67da22d23f introducing net-tcp-fastopen feature: $ git bisect bad cf60af03ca4e71134206809ea892e49b92a88896 cf60af03ca4e71134206809ea892e49b92a88896 is the first bad commit commit cf60af03ca4e71134206809ea892e49b92a88896 Author: Yuchung Cheng <ych...@google.com> Date: Thu Jul 19 06:43:09 2012 +0000 So, ideally, the upstream commit ac6e780070 which fixes the bug should have "Fixes: cf60af03ca" statement, unfortunately, this investigation was not completed at the time the patch was accepted upstream. And unfortunately I do not see other way to add this information except making notes in a comment in the related code, which seems weird. Best regards, Vladis Dronov | Red Hat, Inc. | Product Security Engineer
