[PATCH net] tcp: fix DSACK-based undo on non-duplicate ACK

[PATCH net] tcp: fix DSACK-based undo on non-duplicate ACK

[Priyaranjan Jha]

Fixes DSACK-based undo when sender is in Open State and
an ACK advances snd_una.

Example scenario:
- Sender goes into recovery and makes some spurious rtx.
- It comes out of recovery and enters into open state.
- It sends some more packets, let's say 4.
- The receiver sends an ACK for the first two, but this ACK is lost.
- The sender receives ack for first two, and DSACK for previous
  spurious rtx.

Signed-off-by: Priyaranjan Jha <priyarjha@google.com>
Signed-off-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Acked-by: Yousuk Seung <ysseung@google.com>
---
 net/ipv4/tcp_input.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 7eec3383702b..bf69bfbe593b 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -114,7 +114,7 @@ int sysctl_tcp_invalid_ratelimit __read_mostly = HZ/2;
 
 #define FLAG_ACKED		(FLAG_DATA_ACKED|FLAG_SYN_ACKED)
 #define FLAG_NOT_DUP		(FLAG_DATA|FLAG_WIN_UPDATE|FLAG_ACKED)
-#define FLAG_CA_ALERT		(FLAG_DATA_SACKED|FLAG_ECE)
+#define FLAG_CA_ALERT		(FLAG_DATA_SACKED|FLAG_ECE|FLAG_DSACKING_ACK)
 #define FLAG_FORWARD_PROGRESS	(FLAG_ACKED|FLAG_DATA_SACKED)
 
 #define TCP_REMNANT (TCP_FLAG_FIN|TCP_FLAG_URG|TCP_FLAG_SYN|TCP_FLAG_PSH)
-- 
2.15.0.403.gc27cc4dac6-goog

Re: [PATCH net] tcp: fix DSACK-based undo on non-duplicate ACK

[David Miller]

From: Priyaranjan Jha <priyarjha@google.com>
Date: Fri,  3 Nov 2017 17:46:55 -0700

> Fixes DSACK-based undo when sender is in Open State and
> an ACK advances snd_una.
> 
> Example scenario:
> - Sender goes into recovery and makes some spurious rtx.
> - It comes out of recovery and enters into open state.
> - It sends some more packets, let's say 4.
> - The receiver sends an ACK for the first two, but this ACK is lost.
> - The sender receives ack for first two, and DSACK for previous
>   spurious rtx.
> 
> Signed-off-by: Priyaranjan Jha <priyarjha@google.com>
> Signed-off-by: Yuchung Cheng <ycheng@google.com>
> Signed-off-by: Neal Cardwell <ncardwell@google.com>
> Acked-by: Yousuk Seung <ysseung@google.com>

Applied, thanks.