Skip to contentSkip to conversation

tcp: ignore Fast Open on repair mode

PATCH In review Yuchung Cheng 2 participants 2 messages Apr 25, 2018 – Apr 27, 2018

Subsystems (3)
Networking Network drivers TCP
lore
Share & tools
lore

Yuchung Cheng

author
#0 lore raw

PATCH 1/1 tcp: ignore Fast Open on repair mode

The TCP repair sequence of operation is to first set the socket in repair mode, then inject the TCP stats into the socket with repair socket options, then call connect() to re-activate the socket. The connect syscall simply returns and set state to ESTABLISHED mode. As a result Fast Open is meaningless for TCP repair.

However allowing sendto() system call with MSG_FASTOPEN flag half-way during the repair operation could unexpectedly cause data to be sent, before the operation finishes changing the internal TCP stats (e.g. MSS). This in turn triggers TCP warnings on inconsistent packet accounting.

The fix is to simply disallow Fast Open operation once the socket is in the repair mode.

Reported-by syzbot <[email protected]>
Signed-off-by Yuchung Cheng <[email protected]>
Reviewed-by Neal Cardwell <[email protected]>
Reviewed-by Eric Dumazet <[email protected]>
---
 net/ipv4/tcp.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)
net/ipv4/tcp.c +2 -1
index 9ce1c726185e..4b18ad41d4df 100644
@@ -1204,7 +1204,8 @@ int tcp_sendmsg_locked(struct sock *sk, struct msghdr *msg, size_t size)
 			uarg->zerocopy = 0;
 	}
 
-	if (unlikely(flags & MSG_FASTOPEN || inet_sk(sk)->defer_connect)) {
+	if (unlikely(flags & MSG_FASTOPEN || inet_sk(sk)->defer_connect) &&
+	    !tp->repair) {
 		err = tcp_sendmsg_fastopen(sk, msg, &copied_syn, size);
 		if (err == -EINPROGRESS && copied_syn > 0)
 			goto out;
Signature · 1 line
2.17.0.441.gb46fe60e1d-goog
maintainer
#1 lore raw

From: Yuchung Cheng <[email protected]>
Date: Wed, 25 Apr 2018 11:33:08 -0700

Quoted 12 lines

The TCP repair sequence of operation is to first set the socket in repair mode, then inject the TCP stats into the socket with repair socket options, then call connect() to re-activate the socket. The connect syscall simply returns and set state to ESTABLISHED mode. As a result Fast Open is meaningless for TCP repair.

However allowing sendto() system call with MSG_FASTOPEN flag half-way during the repair operation could unexpectedly cause data to be sent, before the operation finishes changing the internal TCP stats (e.g. MSS). This in turn triggers TCP warnings on inconsistent packet accounting.

Quoted 7 lines

The fix is to simply disallow Fast Open operation once the socket is in the repair mode.

Reported-by syzbot <[email protected]>
Signed-off-by Yuchung Cheng <[email protected]>
Reviewed-by Neal Cardwell <[email protected]>
Reviewed-by Eric Dumazet <[email protected]>

Applied and queued up for -stable, thanks Yuchung.