Patchwork tcp: missing check ACK flag of received segment in FIN-WAIT-2 state

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Submitter Wei Yongjun
Date June 25, 2009, 8:29 a.m.
Message ID <4A43356B.7060005@cn.fujitsu.com>
Download mbox | patch
Permalink /patch/29164/
State Accepted
Delegated to: David Miller
Headers show

Comments

Wei Yongjun - June 25, 2009, 8:29 a.m.
RFC0793 defined that in FIN-WAIT-2 state if the ACK bit is off drop
the segment and return[Page 72]. But this check is missing in function
tcp_timewait_state_process(). This cause the segment with FIN flag but
no ACK has two diffent action:

Case 1:
    Node A                      Node B
              <-------------    FIN,ACK
                                (enter FIN-WAIT-1)
    ACK       ------------->
                                (enter FIN-WAIT-2)
    FIN       ------------->    discard
                                (move sk to tw list)

Case 2:
    Node A                      Node B
              <-------------    FIN,ACK
                                (enter FIN-WAIT-1)
    ACK       ------------->
                                (enter FIN-WAIT-2)
                                (move sk to tw list)
    FIN       ------------->

              <-------------    ACK

This patch fixed the problem.

Signed-off-by: Wei Yongjun <yjwei@cn.fujitsu.com>
---
 net/ipv4/tcp_minisocks.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)
David Miller - June 26, 2009, 3:09 a.m.
From: Wei Yongjun <yjwei@cn.fujitsu.com>
Date: Thu, 25 Jun 2009 16:29:31 +0800

> RFC0793 defined that in FIN-WAIT-2 state if the ACK bit is off drop
> the segment and return[Page 72]. But this check is missing in function
> tcp_timewait_state_process(). This cause the segment with FIN flag but
> no ACK has two diffent action:
...
> This patch fixed the problem.
> 
> Signed-off-by: Wei Yongjun <yjwei@cn.fujitsu.com>

Patch applied, thank you.
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Patch

diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index 43bbba7..f8d67cc 100644
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -128,7 +128,8 @@  tcp_timewait_state_process(struct inet_timewait_sock *tw, struct sk_buff *skb,
 			goto kill_with_rst;
 
 		/* Dup ACK? */
-		if (!after(TCP_SKB_CB(skb)->end_seq, tcptw->tw_rcv_nxt) ||
+		if (!th->ack ||
+		    !after(TCP_SKB_CB(skb)->end_seq, tcptw->tw_rcv_nxt) ||
 		    TCP_SKB_CB(skb)->end_seq == TCP_SKB_CB(skb)->seq) {
 			inet_twsk_put(tw);
 			return TCP_TW_SUCCESS;