[PATCH net-next v4 2/2] selftests/net/packetdrill: cover SO_RCVBUF vs the route window clamp

[Shashank Mohan Jain <jain.sm@gmail.com>]

Add packetdrill tests for the interaction between SO_RCVBUF, a user
TCP_WINDOW_CLAMP and the route "window" metric (RTAX_WINDOW).

Active open, checked on the SYN:

 - tcp_rcvbuf_before_connect_window.pkt: SO_RCVBUF set before connect()
   must not defeat the route metric.

 - tcp_window_clamp_vs_rcvbuf.pkt: a clamp set with TCP_WINDOW_CLAMP must
   not be overwritten by a later SO_RCVBUF on the unconnected socket.

 - tcp_window_clamp_reset_rcvbuf.pkt: TCP_WINDOW_CLAMP=0 removes the
   user's clamp, so a later SO_RCVBUF must again not defeat the route
   metric.

 - tcp_fastopen_connect_rcvbuf_window.pkt: with TCP_FASTOPEN_CONNECT the
   SYN is deferred to the first write() while the socket sits in
   TCP_SYN_SENT; SO_RCVBUF applied in that gap must not defeat the route
   metric either.

Passive open, checked on the SYN-ACK and on the child:

 - tcp_rcvbuf_listener_window.pkt: SO_RCVBUF on the listener must not
   defeat the route metric.

 - tcp_window_clamp_vs_rcvbuf_listener.pkt: TCP_WINDOW_CLAMP and then
   SO_RCVBUF on the listener; the SYN-ACK must use the user's clamp.

 - tcp_syncookies_rcvbuf_window_ip4.pkt and its _ip6 twin: with
   net.ipv4.tcp_syncookies=2, the child created from the cookie must use
   the window scale the SYN-ACK advertised (tcpi_rcv_wscale).

Established socket:

 - tcp_window_clamp_rcvbuf_raise.pkt: after tcp_init_buffer_space()
   lowered window_clamp, a larger SO_RCVBUF must raise it again, up to
   the value set with TCP_WINDOW_CLAMP and not beyond.

All nine tests fail without the previous patch and pass with it. They
are picked up by the packetdrill selftest Makefile
(TEST_PROGS := $(wildcard *.pkt)).

Assisted-by: LLM
Signed-off-by: Shashank Mohan Jain <jain.sm@gmail.com>
---
v4:
 - symbolic TCP_FASTOPEN_CONNECT / TCP_FASTOPEN_NO_COOKIE
 - new: listener (SYN-ACK) tests, SYN cookie tests for IPv4 and IPv6,
   TCP_WINDOW_CLAMP=0 reset test, SO_RCVBUF raise test

 .../tcp_fastopen_connect_rcvbuf_window.pkt    | 21 +++++++++++++++
 .../tcp_rcvbuf_before_connect_window.pkt      | 27 +++++++++++++++++++
 .../tcp_rcvbuf_listener_window.pkt            | 20 ++++++++++++++
 .../tcp_syncookies_rcvbuf_window_ip4.pkt      | 22 +++++++++++++++
 .../tcp_syncookies_rcvbuf_window_ip6.pkt      | 22 +++++++++++++++
 .../tcp_window_clamp_rcvbuf_raise.pkt         | 27 +++++++++++++++++++
 .../tcp_window_clamp_reset_rcvbuf.pkt         | 22 +++++++++++++++
 .../tcp_window_clamp_vs_rcvbuf.pkt            | 23 ++++++++++++++++
 .../tcp_window_clamp_vs_rcvbuf_listener.pkt   | 25 +++++++++++++++++
 9 files changed, 209 insertions(+)
 create mode 100644 tools/testing/selftests/net/packetdrill/tcp_fastopen_connect_rcvbuf_window.pkt
 create mode 100644 tools/testing/selftests/net/packetdrill/tcp_rcvbuf_before_connect_window.pkt
 create mode 100644 tools/testing/selftests/net/packetdrill/tcp_rcvbuf_listener_window.pkt
 create mode 100644 tools/testing/selftests/net/packetdrill/tcp_syncookies_rcvbuf_window_ip4.pkt
 create mode 100644 tools/testing/selftests/net/packetdrill/tcp_syncookies_rcvbuf_window_ip6.pkt
 create mode 100644 tools/testing/selftests/net/packetdrill/tcp_window_clamp_rcvbuf_raise.pkt
 create mode 100644 tools/testing/selftests/net/packetdrill/tcp_window_clamp_reset_rcvbuf.pkt
 create mode 100644 tools/testing/selftests/net/packetdrill/tcp_window_clamp_vs_rcvbuf.pkt
 create mode 100644 tools/testing/selftests/net/packetdrill/tcp_window_clamp_vs_rcvbuf_listener.pkt

diff --git a/tools/testing/selftests/net/packetdrill/tcp_fastopen_connect_rcvbuf_window.pkt b/tools/testing/selftests/net/packetdrill/tcp_fastopen_connect_rcvbuf_window.pkt
new file mode 100644
index 00000000000..b297294ed16
--- /dev/null
+++ b/tools/testing/selftests/net/packetdrill/tcp_fastopen_connect_rcvbuf_window.pkt
@@ -0,0 +1,21 @@
+// SPDX-License-Identifier: GPL-2.0
+// TCP_FASTOPEN_CONNECT defers the SYN until the first write(); between
+// connect() and that write the socket is in TCP_SYN_SENT. SO_RCVBUF applied
+// in that gap must not defeat the route "window" metric on the deferred SYN.
+--ip_version=ipv4
+
+`./defaults.sh
+sysctl -q net.ipv4.tcp_fastopen=5
+ip route replace 192.0.2.1 via 192.168.0.1 dev tun0 window 4096`
+
+    0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
+   +0 setsockopt(3, SOL_TCP, TCP_FASTOPEN_CONNECT, [1], 4) = 0
+   +0 setsockopt(3, SOL_TCP, TCP_FASTOPEN_NO_COOKIE, [1], 4) = 0
+   +0 connect(3, ..., ...) = 0
+   +0 setsockopt(3, SOL_SOCKET, SO_RCVBUF, [1048576], 4) = 0
+   +0 fcntl(3, F_SETFL, O_RDWR|O_NONBLOCK) = 0
+   +0 write(3, ..., 1) = 1
+
+// The deferred SYN (carrying 1 byte of data) must advertise the route
+// clamped window and window scale 0 (not win 65535, wscale 5).
+   +0 > S 0:1(1) win 2920 <mss 1460,sackOK,TS val 0 ecr 0,nop,wscale 0>
diff --git a/tools/testing/selftests/net/packetdrill/tcp_rcvbuf_before_connect_window.pkt b/tools/testing/selftests/net/packetdrill/tcp_rcvbuf_before_connect_window.pkt
new file mode 100644
index 00000000000..7ec7f14d8e8
--- /dev/null
+++ b/tools/testing/selftests/net/packetdrill/tcp_rcvbuf_before_connect_window.pkt
@@ -0,0 +1,27 @@
+// SPDX-License-Identifier: GPL-2.0
+// Setting SO_RCVBUF before connect() must not defeat the route "window"
+// metric on the SYN.
+//
+// The route to the peer carries "window 4096" (RTAX_WINDOW). With SO_RCVBUF
+// also set before connect(), the SYN the kernel sends must still advertise
+// the small, route-clamped receive window and a window scale of 0 (the
+// window scale option is sent, with a shift of 0).
+//
+// Since commit b025461303d8 ("tcp: update window_clamp when SO_RCVBUF is
+// set"), setsockopt(SO_RCVBUF) wrote tp->window_clamp while the socket was
+// still in TCP_CLOSE. tcp_connect_init() then treated that as a user clamp
+// and skipped RTAX_WINDOW, so the SYN carried win 65535, wscale 5 instead.
+--ip_version=ipv4
+
+`./defaults.sh
+ip route replace 192.0.2.1 via 192.168.0.1 dev tun0 window 4096`
+
+    0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
+   +0 setsockopt(3, SOL_SOCKET, SO_RCVBUF, [1048576], 4) = 0
+   +0 fcntl(3, F_SETFL, O_RDWR|O_NONBLOCK) = 0
+   +0 connect(3, ..., ...) = -1 EINPROGRESS (Operation now in progress)
+
+// The SYN must advertise the route-clamped window and window scale 0.
+   +0 > S 0:0(0) win 2920 <mss 1460,sackOK,TS val 0 ecr 0,nop,wscale 0>
+  +.1 < S. 0:0(0) ack 1 win 65535 <mss 1460,nop,wscale 7>
+   +0 > . 1:1(0) ack 1
diff --git a/tools/testing/selftests/net/packetdrill/tcp_rcvbuf_listener_window.pkt b/tools/testing/selftests/net/packetdrill/tcp_rcvbuf_listener_window.pkt
new file mode 100644
index 00000000000..ed20a75fa9a
--- /dev/null
+++ b/tools/testing/selftests/net/packetdrill/tcp_rcvbuf_listener_window.pkt
@@ -0,0 +1,20 @@
+// SPDX-License-Identifier: GPL-2.0
+// Passive side: SO_RCVBUF set on a listener must not defeat the route
+// "window" metric on the SYN-ACK, and the child must use the window scale
+// that the SYN-ACK advertised.
+--ip_version=ipv4
+
+`./defaults.sh
+ip route replace 192.0.2.1 via 192.168.0.1 dev tun0 window 4096`
+
+    0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
+   +0 setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
+   +0 setsockopt(3, SOL_SOCKET, SO_RCVBUF, [1048576], 4) = 0
+   +0 bind(3, ..., ...) = 0
+   +0 listen(3, 1) = 0
+
+   +0 < S 0:0(0) win 65535 <mss 1460,sackOK,TS val 100 ecr 0,nop,wscale 7>
+   +0 > S. 0:0(0) ack 1 win 2896 <mss 1460,sackOK,TS val 100 ecr 100,nop,wscale 0>
+ +.01 < . 1:1(0) ack 1 win 514 <nop,nop,TS val 110 ecr 100>
+   +0 accept(3, ..., ...) = 4
+   +0 %{ assert tcpi_rcv_wscale == 0, tcpi_rcv_wscale }%
diff --git a/tools/testing/selftests/net/packetdrill/tcp_syncookies_rcvbuf_window_ip4.pkt b/tools/testing/selftests/net/packetdrill/tcp_syncookies_rcvbuf_window_ip4.pkt
new file mode 100644
index 00000000000..e26f78704ab
--- /dev/null
+++ b/tools/testing/selftests/net/packetdrill/tcp_syncookies_rcvbuf_window_ip4.pkt
@@ -0,0 +1,22 @@
+// SPDX-License-Identifier: GPL-2.0
+// SYN cookies: the child built by cookie_v4_check() must use the same
+// window clamp rule as the SYN-ACK. With SO_RCVBUF set on the listener and
+// a route "window" metric, the SYN-ACK advertises window scale 0, so the
+// child must use a receive window scale of 0 too.
+--ip_version=ipv4
+
+`./defaults.sh
+sysctl -q net.ipv4.tcp_syncookies=2
+ip route replace 192.0.2.1 via 192.168.0.1 dev tun0 window 4096`
+
+    0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
+   +0 setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
+   +0 setsockopt(3, SOL_SOCKET, SO_RCVBUF, [1048576], 4) = 0
+   +0 bind(3, ..., ...) = 0
+   +0 listen(3, 10) = 0
+
+   +0 < S 0:0(0) win 65535 <mss 1460,sackOK,TS val 100 ecr 0,nop,wscale 7>
+   +0 > S. 0:0(0) ack 1 win 2896 <mss 1460,sackOK,TS val 4000 ecr 100,nop,wscale 0>
+ +.01 < . 1:1(0) ack 1 win 514 <nop,nop,TS val 110 ecr 4000>
+   +0 accept(3, ..., ...) = 4
+   +0 %{ assert tcpi_rcv_wscale == 0, tcpi_rcv_wscale }%
diff --git a/tools/testing/selftests/net/packetdrill/tcp_syncookies_rcvbuf_window_ip6.pkt b/tools/testing/selftests/net/packetdrill/tcp_syncookies_rcvbuf_window_ip6.pkt
new file mode 100644
index 00000000000..8b5dd71d765
--- /dev/null
+++ b/tools/testing/selftests/net/packetdrill/tcp_syncookies_rcvbuf_window_ip6.pkt
@@ -0,0 +1,22 @@
+// SPDX-License-Identifier: GPL-2.0
+// SYN cookies: the child built by cookie_v6_check() must use the same
+// window clamp rule as the SYN-ACK. With SO_RCVBUF set on the listener and
+// a route "window" metric, the SYN-ACK advertises window scale 0, so the
+// child must use a receive window scale of 0 too.
+--ip_version=ipv6
+
+`./defaults.sh
+sysctl -q net.ipv4.tcp_syncookies=2
+ip -6 route replace fd3d:fa7b:d17d::1 via fd3d:0a0b:17d6:8888::1 dev tun0 window 4096`
+
+    0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
+   +0 setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
+   +0 setsockopt(3, SOL_SOCKET, SO_RCVBUF, [1048576], 4) = 0
+   +0 bind(3, ..., ...) = 0
+   +0 listen(3, 10) = 0
+
+   +0 < S 0:0(0) win 65535 <mss 1460,sackOK,TS val 100 ecr 0,nop,wscale 7>
+   +0 > S. 0:0(0) ack 1 win 2896 <mss 1460,sackOK,TS val 4000 ecr 100,nop,wscale 0>
+ +.01 < . 1:1(0) ack 1 win 514 <nop,nop,TS val 110 ecr 4000>
+   +0 accept(3, ..., ...) = 4
+   +0 %{ assert tcpi_rcv_wscale == 0, tcpi_rcv_wscale }%
diff --git a/tools/testing/selftests/net/packetdrill/tcp_window_clamp_rcvbuf_raise.pkt b/tools/testing/selftests/net/packetdrill/tcp_window_clamp_rcvbuf_raise.pkt
new file mode 100644
index 00000000000..08ef005bf99
--- /dev/null
+++ b/tools/testing/selftests/net/packetdrill/tcp_window_clamp_rcvbuf_raise.pkt
@@ -0,0 +1,27 @@
+// SPDX-License-Identifier: GPL-2.0
+// After the handshake, tcp_init_buffer_space() lowers window_clamp to the
+// receive space. A later, larger SO_RCVBUF must raise window_clamp again,
+// but only up to the clamp the user set with TCP_WINDOW_CLAMP.
+//
+// packetdrill has no symbol for TCP_WINDOW_CLAMP, so optname 10 is used.
+--ip_version=ipv4
+
+`./defaults.sh`
+
+    0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
+   +0 setsockopt(3, SOL_TCP, 10, [40000], 4) = 0
+   +0 setsockopt(3, SOL_SOCKET, SO_RCVBUF, [8192], 4) = 0
+   +0 fcntl(3, F_SETFL, O_RDWR|O_NONBLOCK) = 0
+   +0 connect(3, ..., ...) = -1 EINPROGRESS (Operation now in progress)
+   +0 > S 0:0(0) <...>
+  +.1 < S. 0:0(0) ack 1 win 65535 <mss 1460,nop,wscale 7>
+   +0 > . 1:1(0) ack 1
+
+// The small receive buffer keeps window_clamp below the user's clamp:
+// 8192 (tcp_full_space()) minus the one segment (advmss 1460) that
+// tcp_init_buffer_space() reserves.
+   +0 getsockopt(3, SOL_TCP, 10, [6732], [4]) = 0
+
+// A larger SO_RCVBUF raises it again, up to the user's clamp.
+   +0 setsockopt(3, SOL_SOCKET, SO_RCVBUF, [212992], 4) = 0
+   +0 getsockopt(3, SOL_TCP, 10, [40000], [4]) = 0
diff --git a/tools/testing/selftests/net/packetdrill/tcp_window_clamp_reset_rcvbuf.pkt b/tools/testing/selftests/net/packetdrill/tcp_window_clamp_reset_rcvbuf.pkt
new file mode 100644
index 00000000000..458f2f313c7
--- /dev/null
+++ b/tools/testing/selftests/net/packetdrill/tcp_window_clamp_reset_rcvbuf.pkt
@@ -0,0 +1,22 @@
+// SPDX-License-Identifier: GPL-2.0
+// TCP_WINDOW_CLAMP set back to 0 on an unconnected socket removes the
+// user's clamp: a later SO_RCVBUF must then not stop the route "window"
+// metric from being applied on the SYN.
+//
+// packetdrill has no symbol for TCP_WINDOW_CLAMP, so optname 10 is used.
+--ip_version=ipv4
+
+`./defaults.sh
+ip route replace 192.0.2.1 via 192.168.0.1 dev tun0 window 4096`
+
+    0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
+   +0 setsockopt(3, SOL_TCP, 10, [16384], 4) = 0
+   +0 setsockopt(3, SOL_TCP, 10, [0], 4) = 0
+   +0 setsockopt(3, SOL_SOCKET, SO_RCVBUF, [1048576], 4) = 0
+   +0 fcntl(3, F_SETFL, O_RDWR|O_NONBLOCK) = 0
+   +0 connect(3, ..., ...) = -1 EINPROGRESS (Operation now in progress)
+
+// No user clamp is left, so the SYN advertises the route window.
+   +0 > S 0:0(0) win 2920 <mss 1460,sackOK,TS val 0 ecr 0,nop,wscale 0>
+  +.1 < S. 0:0(0) ack 1 win 65535 <mss 1460,nop,wscale 7>
+   +0 > . 1:1(0) ack 1
diff --git a/tools/testing/selftests/net/packetdrill/tcp_window_clamp_vs_rcvbuf.pkt b/tools/testing/selftests/net/packetdrill/tcp_window_clamp_vs_rcvbuf.pkt
new file mode 100644
index 00000000000..69a05959e42
--- /dev/null
+++ b/tools/testing/selftests/net/packetdrill/tcp_window_clamp_vs_rcvbuf.pkt
@@ -0,0 +1,23 @@
+// SPDX-License-Identifier: GPL-2.0
+// A window clamp the user set with setsockopt(TCP_WINDOW_CLAMP) must be
+// honoured on the SYN even when SO_RCVBUF is set afterwards on the still
+// unconnected socket: SO_RCVBUF must not raise window_clamp above the
+// user's clamp, and the route "window" metric must not replace it either.
+//
+// packetdrill has no symbol for TCP_WINDOW_CLAMP, so optname 10 is used.
+--ip_version=ipv4
+
+`./defaults.sh
+ip route replace 192.0.2.1 via 192.168.0.1 dev tun0 window 4096`
+
+    0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
+   +0 setsockopt(3, SOL_TCP, 10, [16384], 4) = 0
+   +0 setsockopt(3, SOL_SOCKET, SO_RCVBUF, [1048576], 4) = 0
+   +0 fcntl(3, F_SETFL, O_RDWR|O_NONBLOCK) = 0
+   +0 connect(3, ..., ...) = -1 EINPROGRESS (Operation now in progress)
+
+// The SYN advertises the user's clamp (win 16060), not the route window
+// (2920) and not the SO_RCVBUF-derived full window.
+   +0 > S 0:0(0) win 16060 <mss 1460,sackOK,TS val 0 ecr 0,nop,wscale 0>
+  +.1 < S. 0:0(0) ack 1 win 65535 <mss 1460,nop,wscale 7>
+   +0 > . 1:1(0) ack 1
diff --git a/tools/testing/selftests/net/packetdrill/tcp_window_clamp_vs_rcvbuf_listener.pkt b/tools/testing/selftests/net/packetdrill/tcp_window_clamp_vs_rcvbuf_listener.pkt
new file mode 100644
index 00000000000..f7e7ddb5000
--- /dev/null
+++ b/tools/testing/selftests/net/packetdrill/tcp_window_clamp_vs_rcvbuf_listener.pkt
@@ -0,0 +1,25 @@
+// SPDX-License-Identifier: GPL-2.0
+// Passive side: a TCP_WINDOW_CLAMP set on a listener must be honoured on
+// the SYN-ACK even when SO_RCVBUF is set afterwards on the listener, and
+// the route "window" metric must not replace it.
+//
+// packetdrill has no symbol for TCP_WINDOW_CLAMP, so optname 10 is used.
+--ip_version=ipv4
+
+`./defaults.sh
+ip route replace 192.0.2.1 via 192.168.0.1 dev tun0 window 4096`
+
+    0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
+   +0 setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
+   +0 setsockopt(3, SOL_TCP, 10, [16384], 4) = 0
+   +0 setsockopt(3, SOL_SOCKET, SO_RCVBUF, [1048576], 4) = 0
+   +0 bind(3, ..., ...) = 0
+   +0 listen(3, 1) = 0
+
+// The SYN-ACK advertises the user's clamp, not the route window and not
+// the SO_RCVBUF-derived full window.
+   +0 < S 0:0(0) win 65535 <mss 1460,sackOK,TS val 100 ecr 0,nop,wscale 7>
+   +0 > S. 0:0(0) ack 1 win 15928 <mss 1460,sackOK,TS val 100 ecr 100,nop,wscale 0>
+ +.01 < . 1:1(0) ack 1 win 514 <nop,nop,TS val 110 ecr 100>
+   +0 accept(3, ..., ...) = 4
+   +0 %{ assert tcpi_rcv_wscale == 0, tcpi_rcv_wscale }%
-- 
2.43.0