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Denis Kirjanov cb22ce3346 tcp: don't ignore ECN CWR on pure ACK
[ Upstream commit 2570284060b48f3f79d8f1a2698792f36c385e9a ]

there is a problem with the CWR flag set in an incoming ACK segment
and it leads to the situation when the ECE flag is latched forever

the following packetdrill script shows what happens:

// Stack receives incoming segments with CE set
+0.1 <[ect0]  . 11001:12001(1000) ack 1001 win 65535
+0.0 <[ce]    . 12001:13001(1000) ack 1001 win 65535
+0.0 <[ect0] P. 13001:14001(1000) ack 1001 win 65535

// Stack repsonds with ECN ECHO
+0.0 >[noecn]  . 1001:1001(0) ack 12001
+0.0 >[noecn] E. 1001:1001(0) ack 13001
+0.0 >[noecn] E. 1001:1001(0) ack 14001

// Write a packet
+0.1 write(3, ..., 1000) = 1000
+0.0 >[ect0] PE. 1001:2001(1000) ack 14001

// Pure ACK received
+0.01 <[noecn] W. 14001:14001(0) ack 2001 win 65535

// Since CWR was sent, this packet should NOT have ECE set

+0.1 write(3, ..., 1000) = 1000
+0.0 >[ect0]  P. 2001:3001(1000) ack 14001
// but Linux will still keep ECE latched here, with packetdrill
// flagging a missing ECE flag, expecting
// >[ect0] PE. 2001:3001(1000) ack 14001
// in the script

In the situation above we will continue to send ECN ECHO packets
and trigger the peer to reduce the congestion window. To avoid that
we can check CWR on pure ACKs received.

v3:
- Add a sequence check to avoid sending an ACK to an ACK

v2:
- Adjusted the comment
- move CWR check before checking for unacknowledged packets

Signed-off-by: Denis Kirjanov <denis.kirjanov@suse.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2020-06-30 15:36:45 -04:00
arch kretprobe: Prevent triggering kretprobe from within kprobe_flush_task 2020-06-24 17:50:52 +02:00
block block/bio-integrity: don't free 'buf' if bio_integrity_add_page() failed 2020-06-30 15:36:43 -04:00
certs
crypto crypto: algboss - don't wait during notifier callback 2020-06-24 17:50:51 +02:00
Documentation dt-bindings: display: mediatek: control dpi pins mode to avoid leakage 2020-06-22 09:30:58 +02:00
drivers rocker: fix incorrect error handling in dma_rings_init 2020-06-30 15:36:45 -04:00
fs f2fs: avoid utf8_strncasecmp() with unstable name 2020-06-24 17:50:50 +02:00
include sctp: Don't advertise IPv4 addresses if ipv6only is set on the socket 2020-06-30 15:36:45 -04:00
init x86: Fix early boot crash on gcc-10, third try 2020-05-20 08:20:34 +02:00
ipc
kernel kretprobe: Prevent triggering kretprobe from within kprobe_flush_task 2020-06-24 17:50:52 +02:00
lib lib/zlib: remove outdated and incorrect pre-increment optimization 2020-06-24 17:50:39 +02:00
LICENSES
mm mm: call cond_resched() from deferred_init_memmap() 2020-06-22 09:31:14 +02:00
net tcp: don't ignore ECN CWR on pure ACK 2020-06-30 15:36:45 -04:00
samples samples: bpf: Fix build error 2020-06-03 08:21:15 +02:00
scripts scripts: headers_install: Exit with error on config leak 2020-06-24 17:50:33 +02:00
security selinux: fix double free 2020-06-24 17:50:48 +02:00
sound ASoC: rt5645: Add platform-data for Asus T101HA 2020-06-24 17:50:42 +02:00
tools perf stat: Fix NULL pointer dereference 2020-06-24 17:50:45 +02:00
usr
virt KVM: arm64: Save the host's PtrAuth keys in non-preemptible context 2020-06-17 16:40:38 +02:00
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.cocciconfig
.get_maintainer.ignore
.gitattributes
.gitignore
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COPYING
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Kconfig
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Makefile Linux 5.4.49 2020-06-24 17:50:53 +02:00
README

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There are various text files in the Documentation/ subdirectory,
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