linux.git/net/ipv4/tcp_input.c, branch v5.11

tcp: fix TLP timer not set when CA_STATE changes from DISORDER to OPEN

2021-01-24T05:33:01+00:00

Upon receiving a cumulative ACK that changes the congestion state from
Disorder to Open, the TLP timer is not set. If the sender is app-limited,
it can only wait for the RTO timer to expire and retransmit.

The reason for this is that the TLP timer is set before the congestion
state changes in tcp_ack(), so we delay the time point of calling
tcp_set_xmit_timer() until after tcp_fastretrans_alert() returns and
remove the FLAG_SET_XMIT_TIMER from ack_flag when the RACK reorder timer
is set.

This commit has two additional benefits:
1) Make sure to reset RTO according to RFC6298 when receiving ACK, to
avoid spurious RTO caused by RTO timer early expires.
2) Reduce the xmit timer reschedule once per ACK when the RACK reorder
timer is set.

Fixes: df92c8394e6e ("tcp: fix xmit timer to only be reset if data ACKed/SACKed")
Link: https://lore.kernel.org/netdev/1611311242-6675-1-git-send-email-yangpc@wangsu.com
Signed-off-by: Pengcheng Yang 
Acked-by: Neal Cardwell 
Acked-by: Yuchung Cheng 
Cc: Eric Dumazet 
Link: https://lore.kernel.org/r/1611464834-23030-1-git-send-email-yangpc@wangsu.com
Signed-off-by: Jakub Kicinski

tcp: make TCP_USER_TIMEOUT accurate for zero window probes

2021-01-24T03:32:51+00:00

The TCP_USER_TIMEOUT is checked by the 0-window probe timer. As the
timer has backoff with a max interval of about two minutes, the
actual timeout for TCP_USER_TIMEOUT can be off by up to two minutes.

In this patch the TCP_USER_TIMEOUT is made more accurate by taking it
into account when computing the timer value for the 0-window probes.

This patch is similar to and builds on top of the one that made
TCP_USER_TIMEOUT accurate for RTOs in commit b701a99e431d ("tcp: Add
tcp_clamp_rto_to_user_timeout() helper to improve accuracy").

Fixes: 9721e709fa68 ("tcp: simplify window probe aborting on USER_TIMEOUT")
Signed-off-by: Enke Chen 
Reviewed-by: Neal Cardwell 
Signed-off-by: Eric Dumazet 
Link: https://lore.kernel.org/r/20210122191306.GA99540@localhost.localdomain
Signed-off-by: Jakub Kicinski

tcp: fix TCP socket rehash stats mis-accounting

2021-01-20T03:47:20+00:00

The previous commit 32efcc06d2a1 ("tcp: export count for rehash attempts")
would mis-account rehashing SNMP and socket stats:

  a. During handshake of an active open, only counts the first
     SYN timeout

  b. After handshake of passive and active open, stop updating
     after (roughly) TCP_RETRIES1 recurring RTOs

  c. After the socket aborts, over count timeout_rehash by 1

This patch fixes this by checking the rehash result from sk_rethink_txhash.

Fixes: 32efcc06d2a1 ("tcp: export count for rehash attempts")
Signed-off-by: Yuchung Cheng 
Signed-off-by: Eric Dumazet 
Signed-off-by: Neal Cardwell 
Link: https://lore.kernel.org/r/20210119192619.1848270-1-ycheng@google.com
Signed-off-by: Jakub Kicinski

tcp: fix TCP_USER_TIMEOUT with zero window

2021-01-19T03:59:17+00:00

The TCP session does not terminate with TCP_USER_TIMEOUT when data
remain untransmitted due to zero window.

The number of unanswered zero-window probes (tcp_probes_out) is
reset to zero with incoming acks irrespective of the window size,
as described in tcp_probe_timer():

    RFC 1122 4.2.2.17 requires the sender to stay open indefinitely
    as long as the receiver continues to respond probes. We support
    this by default and reset icsk_probes_out with incoming ACKs.

This counter, however, is the wrong one to be used in calculating the
duration that the window remains closed and data remain untransmitted.
Thanks to Jonathan Maxwell  for diagnosing the
actual issue.

In this patch a new timestamp is introduced for the socket in order to
track the elapsed time for the zero-window probes that have not been
answered with any non-zero window ack.

Fixes: 9721e709fa68 ("tcp: simplify window probe aborting on USER_TIMEOUT")
Reported-by: William McCall 
Co-developed-by: Neal Cardwell 
Signed-off-by: Neal Cardwell 
Signed-off-by: Enke Chen 
Reviewed-by: Yuchung Cheng 
Reviewed-by: Eric Dumazet 
Link: https://lore.kernel.org/r/20210115223058.GA39267@localhost.localdomain
Signed-off-by: Jakub Kicinski

tcp: Add logic to check for SYN w/ data in tcp_simple_retransmit

2020-12-15T03:29:55+00:00

There are cases where a fastopen SYN may trigger either a ICMP_TOOBIG
message in the case of IPv6 or a fragmentation request in the case of
IPv4. This results in the socket stalling for a second or more as it does
not respond to the message by retransmitting the SYN frame.

Normally a SYN frame should not be able to trigger a ICMP_TOOBIG or
ICMP_FRAG_NEEDED however in the case of fastopen we can have a frame that
makes use of the entire MSS. In the case of fastopen it does, and an
additional complication is that the retransmit queue doesn't contain the
original frames. As a result when tcp_simple_retransmit is called and
walks the list of frames in the queue it may not mark the frames as lost
because both the SYN and the data packet each individually are smaller than
the MSS size after the adjustment. This results in the socket being stalled
until the retransmit timer kicks in and forces the SYN frame out again
without the data attached.

In order to resolve this we can reduce the MSS the packets are compared
to in tcp_simple_retransmit to -1 for cases where we are still in the
TCP_SYN_SENT state for a fastopen socket. Doing this we will mark all of
the packets related to the fastopen SYN as lost.

Signed-off-by: Alexander Duyck 
Signed-off-by: Eric Dumazet 
Signed-off-by: Yuchung Cheng 
Link: https://lore.kernel.org/r/160780498125.3272.15437756269539236825.stgit@localhost.localdomain
Signed-off-by: Jakub Kicinski

tcp: parse mptcp options contained in reset packets

2020-12-15T01:30:06+00:00

Because TCP-level resets only affect the subflow, there is a MPTCP
option to indicate that the MPTCP-level connection should be closed
immediately without a mptcp-level fin exchange.

This is the 'MPTCP fast close option'.  It can be carried on ack
segments or TCP resets.  In the latter case, its needed to parse mptcp
options also for reset packets so that MPTCP can act accordingly.

Next patch will add receive side fastclose support in MPTCP.

Acked-by: Matthieu Baerts 
Signed-off-by: Florian Westphal 
Signed-off-by: Mat Martineau 
Signed-off-by: Jakub Kicinski

Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net

2020-12-12T06:29:38+00:00

xdp_return_frame_bulk() needs to pass a xdp_buff
to __xdp_return().

strlcpy got converted to strscpy but here it makes no
functional difference, so just keep the right code.

Conflicts:
	net/netfilter/nf_tables_api.c

Signed-off-by: Jakub Kicinski

tcp: select sane initial rcvq_space.space for big MSS

2020-12-09T00:27:48+00:00

Before commit a337531b942b ("tcp: up initial rmem to 128KB and SYN rwin to around 64KB")
small tcp_rmem[1] values were overridden by tcp_fixup_rcvbuf() to accommodate various MSS.

This is no longer the case, and Hazem Mohamed Abuelfotoh reported
that DRS would not work for MTU 9000 endpoints receiving regular (1500 bytes) frames.

Root cause is that tcp_init_buffer_space() uses tp->rcv_wnd for upper limit
of rcvq_space.space computation, while it can select later a smaller
value for tp->rcv_ssthresh and tp->window_clamp.

ss -temoi on receiver would show :

skmem:(r0,rb131072,t0,tb46080,f0,w0,o0,bl0,d0) rcv_space:62496 rcv_ssthresh:56596

This means that TCP can not increase its window in tcp_grow_window(),
and that DRS can never kick.

Fix this by making sure that rcvq_space.space is not bigger than number of bytes
that can be held in TCP receive queue.

People unable/unwilling to change their kernel can work around this issue by
selecting a bigger tcp_rmem[1] value as in :

echo "4096 196608 6291456" >/proc/sys/net/ipv4/tcp_rmem

Based on an initial report and patch from Hazem Mohamed Abuelfotoh
 https://lore.kernel.org/netdev/20201204180622.14285-1-abuehaze@amazon.com/

Fixes: a337531b942b ("tcp: up initial rmem to 128KB and SYN rwin to around 64KB")
Fixes: 041a14d26715 ("tcp: start receiver buffer autotuning sooner")
Reported-by: Hazem Mohamed Abuelfotoh 
Signed-off-by: Eric Dumazet 
Acked-by: Soheil Hassas Yeganeh 
Signed-off-by: David S. Miller

tcp: merge 'init_req' and 'route_req' functions

2020-12-03T20:56:03+00:00

The Multipath-TCP standard (RFC 8684) says that an MPTCP host should send
a TCP reset if the token in a MP_JOIN request is unknown.

At this time we don't do this, the 3whs completes and the 'new subflow'
is reset afterwards.  There are two ways to allow MPTCP to send the
reset.

1. override 'send_synack' callback and emit the rst from there.
   The drawback is that the request socket gets inserted into the
   listeners queue just to get removed again right away.

2. Send the reset from the 'route_req' function instead.
   This avoids the 'add&remove request socket', but route_req lacks the
   skb that is required to send the TCP reset.

Instead of just adding the skb to that function for MPTCP sake alone,
Paolo suggested to merge init_req and route_req functions.

This saves one indirection from syn processing path and provides the skb
to the merged function at the same time.

'send reset on unknown mptcp join token' is added in next patch.

Suggested-by: Paolo Abeni 
Cc: Eric Dumazet 
Signed-off-by: Florian Westphal 
Signed-off-by: Jakub Kicinski

tcp: avoid slow start during fast recovery on new losses

2020-11-03T01:17:40+00:00

During TCP fast recovery, the congestion control in charge is by
default the Proportional Rate Reduction (PRR) unless the congestion
control module specified otherwise (e.g. BBR).

Previously when tcp_packets_in_flight() is below snd_ssthresh PRR
would slow start upon receiving an ACK that
   1) cumulatively acknowledges retransmitted data
   and
   2) does not detect further lost retransmission

Such conditions indicate the repair is in good steady progress
after the first round trip of recovery. Otherwise PRR adopts the
packet conservation principle to send only the amount that was
newly delivered (indicated by this ACK).

This patch generalizes the previous design principle to include
also the newly sent data beside retransmission: as long as
the delivery is making good progress, both retransmission and
new data should be accounted to make PRR more cautious in slow
starting.

Suggested-by: Matt Mathis 
Suggested-by: Neal Cardwell 
Signed-off-by: Yuchung Cheng 
Signed-off-by: Neal Cardwell 
Signed-off-by: Eric Dumazet 
Link: https://lore.kernel.org/r/20201031013412.1973112-1-ycheng@google.com
Signed-off-by: Jakub Kicinski