[TCP]: MTU probing
Implementation of packetization layer path mtu discovery for TCP, based on
the internet-draft currently found at
<http://www.ietf.org/internet-drafts/draft-ietf-pmtud-method-05.txt>.
Signed-off-by: John Heffner <jheffner@psc.edu>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c
index e188095..7c1bde3 100644
--- a/net/ipv4/tcp_timer.c
+++ b/net/ipv4/tcp_timer.c
@@ -119,8 +119,10 @@
/* A write timeout has occurred. Process the after effects. */
static int tcp_write_timeout(struct sock *sk)
{
- const struct inet_connection_sock *icsk = inet_csk(sk);
+ struct inet_connection_sock *icsk = inet_csk(sk);
+ struct tcp_sock *tp = tcp_sk(sk);
int retry_until;
+ int mss;
if ((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV)) {
if (icsk->icsk_retransmits)
@@ -128,25 +130,19 @@
retry_until = icsk->icsk_syn_retries ? : sysctl_tcp_syn_retries;
} else {
if (icsk->icsk_retransmits >= sysctl_tcp_retries1) {
- /* NOTE. draft-ietf-tcpimpl-pmtud-01.txt requires pmtu black
- hole detection. :-(
-
- It is place to make it. It is not made. I do not want
- to make it. It is disgusting. It does not work in any
- case. Let me to cite the same draft, which requires for
- us to implement this:
-
- "The one security concern raised by this memo is that ICMP black holes
- are often caused by over-zealous security administrators who block
- all ICMP messages. It is vitally important that those who design and
- deploy security systems understand the impact of strict filtering on
- upper-layer protocols. The safest web site in the world is worthless
- if most TCP implementations cannot transfer data from it. It would
- be far nicer to have all of the black holes fixed rather than fixing
- all of the TCP implementations."
-
- Golden words :-).
- */
+ /* Black hole detection */
+ if (sysctl_tcp_mtu_probing) {
+ if (!icsk->icsk_mtup.enabled) {
+ icsk->icsk_mtup.enabled = 1;
+ tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
+ } else {
+ mss = min(sysctl_tcp_base_mss,
+ tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low)/2);
+ mss = max(mss, 68 - tp->tcp_header_len);
+ icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, mss);
+ tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
+ }
+ }
dst_negative_advice(&sk->sk_dst_cache);
}