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author | Jason Baron <jbaron@akamai.com> | 2017-01-17 13:37:19 -0500 |
---|---|---|
committer | David S. Miller <davem@davemloft.net> | 2017-01-17 15:51:55 -0500 |
commit | 0e40f4c9593ba2c7c30150ed669da97bd581c0cd (patch) | |
tree | 274f40b12fadf479f3579290c406cbf93c4857b6 /net | |
parent | a870a97757dd4f165f4f7bb749350bee7df31716 (diff) | |
download | linux-stable-0e40f4c9593ba2c7c30150ed669da97bd581c0cd.tar.gz linux-stable-0e40f4c9593ba2c7c30150ed669da97bd581c0cd.tar.bz2 linux-stable-0e40f4c9593ba2c7c30150ed669da97bd581c0cd.zip |
tcp: accept RST for rcv_nxt - 1 after receiving a FIN
Using a Mac OSX box as a client connecting to a Linux server, we have found
that when certain applications (such as 'ab'), are abruptly terminated
(via ^C), a FIN is sent followed by a RST packet on tcp connections. The
FIN is accepted by the Linux stack but the RST is sent with the same
sequence number as the FIN, and Linux responds with a challenge ACK per
RFC 5961. The OSX client then sometimes (they are rate-limited) does not
reply with any RST as would be expected on a closed socket.
This results in sockets accumulating on the Linux server left mostly in
the CLOSE_WAIT state, although LAST_ACK and CLOSING are also possible.
This sequence of events can tie up a lot of resources on the Linux server
since there may be a lot of data in write buffers at the time of the RST.
Accepting a RST equal to rcv_nxt - 1, after we have already successfully
processed a FIN, has made a significant difference for us in practice, by
freeing up unneeded resources in a more expedient fashion.
A packetdrill test demonstrating the behavior:
// testing mac osx rst behavior
// Establish a connection
0.000 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
0.000 setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
0.000 bind(3, ..., ...) = 0
0.000 listen(3, 1) = 0
0.100 < S 0:0(0) win 32768 <mss 1460,nop,wscale 10>
0.100 > S. 0:0(0) ack 1 <mss 1460,nop,wscale 5>
0.200 < . 1:1(0) ack 1 win 32768
0.200 accept(3, ..., ...) = 4
// Client closes the connection
0.300 < F. 1:1(0) ack 1 win 32768
// now send rst with same sequence
0.300 < R. 1:1(0) ack 1 win 32768
// make sure we are in TCP_CLOSE
0.400 %{
assert tcpi_state == 7
}%
Signed-off-by: Jason Baron <jbaron@akamai.com>
Cc: Eric Dumazet <edumazet@google.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net')
-rw-r--r-- | net/ipv4/tcp_input.c | 28 |
1 files changed, 25 insertions, 3 deletions
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index 1a34e9278c07..bfa165cc455a 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -5199,6 +5199,23 @@ static int tcp_copy_to_iovec(struct sock *sk, struct sk_buff *skb, int hlen) return err; } +/* Accept RST for rcv_nxt - 1 after a FIN. + * When tcp connections are abruptly terminated from Mac OSX (via ^C), a + * FIN is sent followed by a RST packet. The RST is sent with the same + * sequence number as the FIN, and thus according to RFC 5961 a challenge + * ACK should be sent. However, Mac OSX rate limits replies to challenge + * ACKs on the closed socket. In addition middleboxes can drop either the + * challenge ACK or a subsequent RST. + */ +static bool tcp_reset_check(const struct sock *sk, const struct sk_buff *skb) +{ + struct tcp_sock *tp = tcp_sk(sk); + + return unlikely(TCP_SKB_CB(skb)->seq == (tp->rcv_nxt - 1) && + (1 << sk->sk_state) & (TCPF_CLOSE_WAIT | TCPF_LAST_ACK | + TCPF_CLOSING)); +} + /* Does PAWS and seqno based validation of an incoming segment, flags will * play significant role here. */ @@ -5237,20 +5254,25 @@ static bool tcp_validate_incoming(struct sock *sk, struct sk_buff *skb, LINUX_MIB_TCPACKSKIPPEDSEQ, &tp->last_oow_ack_time)) tcp_send_dupack(sk, skb); + } else if (tcp_reset_check(sk, skb)) { + tcp_reset(sk); } goto discard; } /* Step 2: check RST bit */ if (th->rst) { - /* RFC 5961 3.2 (extend to match against SACK too if available): - * If seq num matches RCV.NXT or the right-most SACK block, + /* RFC 5961 3.2 (extend to match against (RCV.NXT - 1) after a + * FIN and SACK too if available): + * If seq num matches RCV.NXT or (RCV.NXT - 1) after a FIN, or + * the right-most SACK block, * then * RESET the connection * else * Send a challenge ACK */ - if (TCP_SKB_CB(skb)->seq == tp->rcv_nxt) { + if (TCP_SKB_CB(skb)->seq == tp->rcv_nxt || + tcp_reset_check(sk, skb)) { rst_seq_match = true; } else if (tcp_is_sack(tp) && tp->rx_opt.num_sacks > 0) { struct tcp_sack_block *sp = &tp->selective_acks[0]; |