From 5e8a402f831dbe7ee831340a91439e46f0d38acd Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Fri, 4 Oct 2013 10:31:41 -0700 Subject: tcp: do not forget FIN in tcp_shifted_skb() MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Yuchung found following problem : There are bugs in the SACK processing code, merging part in tcp_shift_skb_data(), that incorrectly resets or ignores the sacked skbs FIN flag. When a receiver first SACK the FIN sequence, and later throw away ofo queue (e.g., sack-reneging), the sender will stop retransmitting the FIN flag, and hangs forever. Following packetdrill test can be used to reproduce the bug. $ cat sack-merge-bug.pkt `sysctl -q net.ipv4.tcp_fack=0` // Establish a connection and send 10 MSS. 0.000 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3 +.000 setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0 +.000 bind(3, ..., ...) = 0 +.000 listen(3, 1) = 0 +.050 < S 0:0(0) win 32792 +.000 > S. 0:0(0) ack 1 +.001 < . 1:1(0) ack 1 win 1024 +.000 accept(3, ..., ...) = 4 +.100 write(4, ..., 12000) = 12000 +.000 shutdown(4, SHUT_WR) = 0 +.000 > . 1:10001(10000) ack 1 +.050 < . 1:1(0) ack 2001 win 257 +.000 > FP. 10001:12001(2000) ack 1 +.050 < . 1:1(0) ack 2001 win 257 +.050 < . 1:1(0) ack 2001 win 257 // SACK reneg +.050 < . 1:1(0) ack 12001 win 257 +0 %{ print "unacked: ",tcpi_unacked }% +5 %{ print "" }% First, a typo inverted left/right of one OR operation, then code forgot to advance end_seq if the merged skb carried FIN. Bug was added in 2.6.29 by commit 832d11c5cd076ab ("tcp: Try to restore large SKBs while SACK processing") Signed-off-by: Eric Dumazet Signed-off-by: Yuchung Cheng Acked-by: Neal Cardwell Cc: Ilpo Järvinen Acked-by: Ilpo Järvinen Signed-off-by: David S. Miller --- net/ipv4/tcp_input.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) (limited to 'net') diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index 25a89eaa669d..113dc5f17d47 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -1284,7 +1284,10 @@ static bool tcp_shifted_skb(struct sock *sk, struct sk_buff *skb, tp->lost_cnt_hint -= tcp_skb_pcount(prev); } - TCP_SKB_CB(skb)->tcp_flags |= TCP_SKB_CB(prev)->tcp_flags; + TCP_SKB_CB(prev)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags; + if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN) + TCP_SKB_CB(prev)->end_seq++; + if (skb == tcp_highest_sack(sk)) tcp_advance_highest_sack(sk, skb); -- cgit v1.2.3