Re: [PATCH] sctp: don't compare hb_timer expire date before starting it

From: kwiecienmaciek@gmail.com
Date: Fri, 22 Feb 2019 09:45:26 +0100

From: Maciej Kwiecien <redacted>

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 <redacted>
Tested-by: Marcin Stojek <redacted>
Signed-off-by: Maciej Kwiecien <redacted>

Applied and queued up for -stable, thank you.