From: Luke Hsiao lukehsiao@google.com
[ Upstream commit e3faa49bcecdfcc80e94dd75709d6acb1a5d89f6 ]
Since the original TFO server code was implemented in commit 168a8f58059a22feb9e9a2dcc1b8053dbbbc12ef ("tcp: TCP Fast Open Server - main code path") the TFO server code has supported the sysctl bit flag TFO_SERVER_COOKIE_NOT_REQD. Currently, when the TFO_SERVER_ENABLE and TFO_SERVER_COOKIE_NOT_REQD sysctl bit flags are set, a server connection will accept a SYN with N bytes of data (N > 0) that has no TFO cookie, create a new fast open connection, process the incoming data in the SYN, and make the connection ready for accepting. After accepting, the connection is ready for read()/recvmsg() to read the N bytes of data in the SYN, ready for write()/sendmsg() calls and data transmissions to transmit data.
This commit changes an edge case in this feature by changing this behavior to apply to (N >= 0) bytes of data in the SYN rather than only (N > 0) bytes of data in the SYN. Now, a server will accept a data-less SYN without a TFO cookie if TFO_SERVER_COOKIE_NOT_REQD is set.
Caveat! While this enables a new kind of TFO (data-less empty-cookie SYN), some firewall rules setup may not work if they assume such packets are not legit TFOs and will filter them.
Signed-off-by: Luke Hsiao lukehsiao@google.com Acked-by: Neal Cardwell ncardwell@google.com Acked-by: Yuchung Cheng ycheng@google.com Signed-off-by: Eric Dumazet edumazet@google.com Link: https://lore.kernel.org/r/20210816205105.2533289-1-luke.w.hsiao@gmail.com Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- net/ipv4/tcp_fastopen.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-)
diff --git a/net/ipv4/tcp_fastopen.c b/net/ipv4/tcp_fastopen.c index 2ab371f55525..119d2c2f3b04 100644 --- a/net/ipv4/tcp_fastopen.c +++ b/net/ipv4/tcp_fastopen.c @@ -342,8 +342,7 @@ struct sock *tcp_try_fastopen(struct sock *sk, struct sk_buff *skb, return NULL; }
- if (syn_data && - tcp_fastopen_no_cookie(sk, dst, TFO_SERVER_COOKIE_NOT_REQD)) + if (tcp_fastopen_no_cookie(sk, dst, TFO_SERVER_COOKIE_NOT_REQD)) goto fastopen;
if (foc->len >= 0 && /* Client presents or requests a cookie */