In RHEL 8 and later, SYN_RECV sockets are not created and "Possible SYN flooding" is not logged when the accept backlog is full.

Issue

In RHEL8 and later, the following behaviors are observed when the accept queue (defined by the backlog argument in listen()) is full:

• When the backlog is full, SYN_RECV sockets are not created, and SYN cookies are not sent.

• The message "Possible SYN flooding on port..." is not logged, even if net.ipv4.tcp_syncookies is set to 2.