Re: [PATCH net] tcp: don't include Fast Open option in SYN-ACK on pure SYN-data

On Thu, Feb 5, 2015 at 7:44 PM, Yuchung Cheng [off-list ref] wrote:

If a server has enabled Fast Open and it receives a pure SYN-data
packet (without a Fast Open option), it won't accept the data but it
incorrectly returns a SYN-ACK with a Fast Open cookie and also
increments the SNMP stat LINUX_MIB_TCPFASTOPENPASSIVEFAIL.

This patch makes the server include a Fast Open cookie in SYN-ACK
only if the SYN has some Fast Open option (i.e., when client
requests or presents a cookie).

Signed-off-by: Yuchung Cheng <redacted>
---
 net/ipv4/tcp_fastopen.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

Acked-by: Neal Cardwell <ncardwell@google.com>

neal