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Subject[PATCH 4.19 238/321] sctp: dont compare hb_timer expire date before starting it
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From: Maciej Kwiecien <maciej.kwiecien@nokia.com>

[ Upstream commit d1f20c03f48102e52eb98b8651d129b83134cae4 ]

hb_timer might not start at all for a particular transport because its
start is conditional. In a result a node is not sending heartbeats.

Function sctp_transport_reset_hb_timer has two roles:
- initial start of hb_timer for a given transport,
- update expire date of hb_timer for a given transport.
The function is optimized to update timer's expire only if it is before
a new calculated one but this comparison is invalid for a timer which
has not yet started. Such a timer has expire == 0 and if a new expire
value is bigger than (MAX_JIFFIES / 2 + 2) then "time_before" macro will
fail and timer will not start resulting in no heartbeat packets send by
the node.

This was found when association was initialized within first 5 mins
after system boot due to jiffies init value which is near to MAX_JIFFIES.

Test kernel version: 4.9.154 (ARCH=arm)
hb_timer.expire = 0; //initialized, not started timer
new_expire = MAX_JIFFIES / 2 + 2; //or more
time_before(hb_timer.expire, new_expire) == false

Fixes: ba6f5e33bdbb ("sctp: avoid refreshing heartbeat timer too often")
Reported-by: Marcin Stojek <marcin.stojek@nokia.com>
Tested-by: Marcin Stojek <marcin.stojek@nokia.com>
Signed-off-by: Maciej Kwiecien <maciej.kwiecien@nokia.com>
Reviewed-by: Alexander Sverdlin <alexander.sverdlin@nokia.com>
Acked-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/sctp/transport.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/sctp/transport.c b/net/sctp/transport.c
index 033696e6f74fb..ad158d311ffae 100644
--- a/net/sctp/transport.c
+++ b/net/sctp/transport.c
@@ -207,7 +207,8 @@ void sctp_transport_reset_hb_timer(struct sctp_transport *transport)

/* When a data chunk is sent, reset the heartbeat interval. */
expires = jiffies + sctp_transport_timeout(transport);
- if (time_before(transport->hb_timer.expires, expires) &&
+ if ((time_before(transport->hb_timer.expires, expires) ||
+ !timer_pending(&transport->hb_timer)) &&
!mod_timer(&transport->hb_timer,
expires + prandom_u32_max(transport->rto)))
sctp_transport_hold(transport);
--
2.20.1


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