linux-stable.git/net/ipv4/tcp_timer.c, branch v4.19.76

tcp: enforce tcp_min_snd_mss in tcp_mtu_probing()

2019-06-17T17:51:56+00:00

commit 967c05aee439e6e5d7d805e195b3a20ef5c433d6 upstream.

If mtu probing is enabled tcp_mtu_probing() could very well end up
with a too small MSS.

Use the new sysctl tcp_min_snd_mss to make sure MSS search
is performed in an acceptable range.

CVE-2019-11479 -- tcp mss hardcoded to 48

Signed-off-by: Eric Dumazet 
Reported-by: Jonathan Lemon 
Cc: Jonathan Looney 
Acked-by: Neal Cardwell 
Cc: Yuchung Cheng 
Cc: Tyler Hicks 
Cc: Bruce Curtis 
Signed-off-by: David S. Miller 
Signed-off-by: Greg Kroah-Hartman

tcp: change txhash on SYN-data timeout

2019-01-22T20:40:30+00:00

[ Upstream commit c5715b8fabfca0ef85903f8bad2189940ed41cc8 ]

Previously upon SYN timeouts the sender recomputes the txhash to
try a different path. However this does not apply on the initial
timeout of SYN-data (active Fast Open). Therefore an active IPv6
Fast Open connection may incur one second RTO penalty to take on
a new path after the second SYN retransmission uses a new flow label.

This patch removes this undesirable behavior so Fast Open changes
the flow label just like the regular connections. This also helps
avoid falsely disabling Fast Open on the sender which triggers
after two consecutive SYN timeouts on Fast Open.

Signed-off-by: Yuchung Cheng 
Reviewed-by: Neal Cardwell 
Signed-off-by: David S. Miller 
Signed-off-by: Greg Kroah-Hartman

tcp: defer SACK compression after DupThresh

2018-12-05T18:32:00+00:00

[ Upstream commit 86de5921a3d5dd246df661e09bdd0a6131b39ae3 ]

Jean-Louis reported a TCP regression and bisected to recent SACK
compression.

After a loss episode (receiver not able to keep up and dropping
packets because its backlog is full), linux TCP stack is sending
a single SACK (DUPACK).

Sender waits a full RTO timer before recovering losses.

While RFC 6675 says in section 5, "Algorithm Details",

   (2) If DupAcks < DupThresh but IsLost (HighACK + 1) returns true --
       indicating at least three segments have arrived above the current
       cumulative acknowledgment point, which is taken to indicate loss
       -- go to step (4).
...
   (4) Invoke fast retransmit and enter loss recovery as follows:

there are old TCP stacks not implementing this strategy, and
still counting the dupacks before starting fast retransmit.

While these stacks probably perform poorly when receivers implement
LRO/GRO, we should be a little more gentle to them.

This patch makes sure we do not enable SACK compression unless
3 dupacks have been sent since last rcv_nxt update.

Ideally we should even rearm the timer to send one or two
more DUPACK if no more packets are coming, but that will
be work aiming for linux-4.21.

Many thanks to Jean-Louis for bisecting the issue, providing
packet captures and testing this patch.

Fixes: 5d9f4262b7ea ("tcp: add SACK compression")
Reported-by: Jean-Louis Dupond 
Tested-by: Jean-Louis Dupond 
Signed-off-by: Eric Dumazet 
Acked-by: Neal Cardwell 
Signed-off-by: David S. Miller 
Signed-off-by: Greg Kroah-Hartman

tcp: make function tcp_retransmit_stamp() static

2018-07-25T23:35:45+00:00

Fixes the following sparse warnings:

net/ipv4/tcp_timer.c:25:5: warning:
 symbol 'tcp_retransmit_stamp' was not declared. Should it be static?

Signed-off-by: Wei Yongjun 
Signed-off-by: David S. Miller

tcp: Add tcp_clamp_rto_to_user_timeout() helper to improve accuracy

2018-07-21T17:28:55+00:00

Create the tcp_clamp_rto_to_user_timeout() helper routine. To calculate
the correct rto, so that the TCP_USER_TIMEOUT socket option is more
accurate. Taking suggestions and feedback into account from
Eric Dumazet, Neal Cardwell and David Laight. Due to the 1st commit we
can avoid the msecs_to_jiffies() and jiffies_to_msecs() dance.

Signed-off-by: Jon Maxwell 
Signed-off-by: Eric Dumazet 
Signed-off-by: David S. Miller

tcp: Add tcp_retransmit_stamp() helper routine

2018-07-21T17:28:55+00:00

Create a seperate helper routine as per Neal Cardwells suggestion. To
be used by the final commit in this series and retransmits_timed_out().

Signed-off-by: Jon Maxwell 
Signed-off-by: Eric Dumazet 
Signed-off-by: David S. Miller

tcp: convert icsk_user_timeout from jiffies to msecs

2018-07-21T17:28:55+00:00

This is a preparatory commit. Part of this series that improves the
socket TCP_USER_TIMEOUT option accuracy. Implement Eric Dumazets idea
to convert icsk->icsk_user_timeout from jiffies to msecs. To eliminate
the msecs_to_jiffies() and jiffies_to_msecs() dance in future.

Signed-off-by: Jon Maxwell 
Signed-off-by: Eric Dumazet 
Signed-off-by: David S. Miller

tcp: add SACK compression

2018-05-18T15:40:27+00:00

When TCP receives an out-of-order packet, it immediately sends
a SACK packet, generating network load but also forcing the
receiver to send 1-MSS pathological packets, increasing its
RTX queue length/depth, and thus processing time.

Wifi networks suffer from this aggressive behavior, but generally
speaking, all these SACK packets add fuel to the fire when networks
are under congestion.

This patch adds a high resolution timer and tp->compressed_ack counter.

Instead of sending a SACK, we program this timer with a small delay,
based on RTT and capped to 1 ms :

	delay = min ( 5 % of RTT, 1 ms)

If subsequent SACKs need to be sent while the timer has not yet
expired, we simply increment tp->compressed_ack.

When timer expires, a SACK is sent with the latest information.
Whenever an ACK is sent (if data is sent, or if in-order
data is received) timer is canceled.

Note that tcp_sack_new_ofo_skb() is able to force a SACK to be sent
if the sack blocks need to be shuffled, even if the timer has not
expired.

A new SNMP counter is added in the following patch.

Two other patches add sysctls to allow changing the 1,000,000 and 44
values that this commit hard-coded.

Signed-off-by: Eric Dumazet 
Acked-by: Neal Cardwell 
Acked-by: Yuchung Cheng 
Acked-by: Toke Høiland-Jørgensen 
Signed-off-by: David S. Miller

tcp: switch pacing timer to softirq based hrtimer

2018-05-11T16:24:37+00:00

linux-4.16 got support for softirq based hrtimers.
TCP can switch its pacing hrtimer to this variant, since this
avoids going through a tasklet and some atomic operations.

pacing timer logic looks like other (jiffies based) tcp timers.

v2: use hrtimer_try_to_cancel() in tcp_clear_xmit_timers()
    to correctly release reference on socket if needed.

Signed-off-by: Eric Dumazet 
Signed-off-by: David S. Miller

tcp: purge write queue upon aborting the connection

2018-03-07T20:01:03+00:00

When the connection is aborted, there is no point in
keeping the packets on the write queue until the connection
is closed.

Similar to a27fd7a8ed38 ('tcp: purge write queue upon RST'),
this is essential for a correct MSG_ZEROCOPY implementation,
because userspace cannot call close(fd) before receiving
zerocopy signals even when the connection is aborted.

Fixes: f214f915e7db ("tcp: enable MSG_ZEROCOPY")
Signed-off-by: Soheil Hassas Yeganeh 
Signed-off-by: Neal Cardwell 
Reviewed-by: Eric Dumazet 
Signed-off-by: Yuchung Cheng 
Signed-off-by: David S. Miller