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Message-ID: <20170807181614.GA16700@caduceus5>
Date: Mon, 7 Aug 2017 11:16:14 -0700
From: Rao Shoaib <rao.shoaib@...cle.com>
To: davem@...emloft.net, kuznet@....inr.ac.ru
Cc: netdev@...r.kernel.org
Subject: [PATCH v1 net] TCP_USER_TIMEOUT and tcp_keepalive should conform to
RFC5482
Change from version 0: Rationale behind the change:
The man page for tcp(7) states
when used with the TCP keepalive (SO_KEEPALIVE) option, TCP_USER_TIMEOUT will
override keepalive to determine when to close a connection due to keepalive
failure.
This is ambigious at best. user expectation is most likely that the connection
will be reset after TCP_USER_TIMEOUT milliseconds of inactivity.
The code however waits for the keepalive to kick-in (default 2hrs) and than
after one failure resets the conenction.
What is the rationale for that ? The same effect can be obtained by simply
changing the value of tcp_keep_alive_probes.
Since the TCP_USER_TIMEOUT option was added based on RFC 5482 we need to follow
the RFC. Which states
4.2 TCP keep-Alives:
Some TCP implementations, such as those in BSD systems, use a
different abort policy for TCP keep-alives than for user data. Thus,
the TCP keep-alive mechanism might abort a connection that would
otherwise have survived the transient period without connectivity.
Therefore, if a connection that enables keep-alives is also using the
TCP User Timeout Option, then the keep-alive timer MUST be set to a
value larger than that of the adopted USER TIMEOUT.
This patch enforces the MUST and also dis-associates user timeout from keep
alive. A man page patch will be submitted separately.
Signed-off-by: Rao Shoaib <rao.shoaib@...cle.com>
---
net/ipv4/tcp.c | 10 ++++++++--
net/ipv4/tcp_timer.c | 9 +--------
2 files changed, 9 insertions(+), 10 deletions(-)
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 71ce33d..f2af44d 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -2628,7 +2628,9 @@ static int do_tcp_setsockopt(struct sock *sk, int level,
break;
case TCP_KEEPIDLE:
- if (val < 1 || val > MAX_TCP_KEEPIDLE)
+ /* Per RFC5482 keepalive_time must be > user_timeout */
+ if (val < 1 || val > MAX_TCP_KEEPIDLE ||
+ ((val * HZ) <= icsk->icsk_user_timeout))
err = -EINVAL;
else {
tp->keepalive_time = val * HZ;
@@ -2724,8 +2726,12 @@ static int do_tcp_setsockopt(struct sock *sk, int level,
case TCP_USER_TIMEOUT:
/* Cap the max time in ms TCP will retry or probe the window
* before giving up and aborting (ETIMEDOUT) a connection.
+ * Per RFC5482 TCP user timeout must be < keepalive_time.
+ * If the default value changes later -- all bets are off.
*/
- if (val < 0)
+ if (val < 0 || (tp->keepalive_time &&
+ tp->keepalive_time <= msecs_to_jiffies(val)) ||
+ net->ipv4.sysctl_tcp_keepalive_time <= msecs_to_jiffies(val))
err = -EINVAL;
else
icsk->icsk_user_timeout = msecs_to_jiffies(val);
diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c
index c0feeee..d39fe60 100644
--- a/net/ipv4/tcp_timer.c
+++ b/net/ipv4/tcp_timer.c
@@ -664,14 +664,7 @@ static void tcp_keepalive_timer (unsigned long data)
elapsed = keepalive_time_elapsed(tp);
if (elapsed >= keepalive_time_when(tp)) {
- /* If the TCP_USER_TIMEOUT option is enabled, use that
- * to determine when to timeout instead.
- */
- if ((icsk->icsk_user_timeout != 0 &&
- elapsed >= icsk->icsk_user_timeout &&
- icsk->icsk_probes_out > 0) ||
- (icsk->icsk_user_timeout == 0 &&
- icsk->icsk_probes_out >= keepalive_probes(tp))) {
+ if (icsk->icsk_probes_out >= keepalive_probes(tp)) {
tcp_send_active_reset(sk, GFP_ATOMIC);
tcp_write_err(sk);
goto out;
--
2.7.4
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