Subject: [PATCH net v2 0/2] tcp: fix handling of stale syncookies timestamps

From: Guillaume Nault <[email-masked]>
Date: Thu, 5 Dec 2019 01:58:58 +0100

The synflood timestamps (->ts_recent_stamp and ->synq_overflow_ts) are
only refreshed when the syncookie protection triggers. Therefore, their
value can become very far apart from jiffies if no synflood happens for
a long time.

If jiffies grows too much and wraps while the synflood timestamp isn't
refreshed, then time_after32() might consider the later to be in the
future. This can trick tcp_synq_no_recent_overflow() into returning
erroneous values and rejecting valid ACKs.

Patch 1 handles the case of ACKs using legitimate syncookies.
Patch 2 handles the case of stray ACKs.

Changes from v1:
  - Initialising timestamps at socket creation time is not enough
    because jiffies wraps in 24 days with HZ=1000 (Eric Dumazet).
    Handle stale timestamps in tcp_synq_overflow() and
    tcp_synq_no_recent_overflow() instead.
  - Rework commit description.
  - Add a second patch to handle the case of stray ACKs.

Guillaume Nault (2):
  tcp: fix rejected syncookies due to stale timestamps
  tcp: tighten acceptance of ACKs not matching a child socket

 include/net/tcp.h | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

-- 
@DaveM, I'm sending both patches in one series as they logically fit
together, although patch 2 is arguably a performance optimisation. I
can drop it from the series and repost it when net-next reopens if
you prefer. Although that'd make the link between the two less obvious.