[TCP]: sysctl to allow TCP window > 32767 sans wscale
Back in the dark ages, we had to be conservative and only allow 15-bit window fields if the window scale option was not negotiated. Some ancient stacks used a signed 16-bit quantity for the window field of the TCP header and would get confused. Those days are long gone, so we can use the full 16-bits by default now. There is a sysctl added so that we can still interact with such old stacks Signed-off-by: Rick Jones <rick.jones2@hp.com> Signed-off-by: David S. Miller <davem@davemloft.net>
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@ -355,6 +355,13 @@ somaxconn - INTEGER
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Defaults to 128. See also tcp_max_syn_backlog for additional tuning
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for TCP sockets.
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tcp_workaround_signed_windows - BOOLEAN
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If set, assume no receipt of a window scaling option means the
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remote TCP is broken and treats the window as a signed quantity.
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If unset, assume the remote TCP is not broken even if we do
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not receive a window scaling option from them.
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Default: 0
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IP Variables:
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ip_local_port_range - 2 INTEGERS
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@ -402,6 +402,7 @@ enum
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NET_IPV4_IPFRAG_MAX_DIST=112,
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NET_TCP_MTU_PROBING=113,
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NET_TCP_BASE_MSS=114,
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NET_IPV4_TCP_WORKAROUND_SIGNED_WINDOWS=115,
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};
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enum {
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@ -224,6 +224,7 @@ extern int sysctl_tcp_tso_win_divisor;
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extern int sysctl_tcp_abc;
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extern int sysctl_tcp_mtu_probing;
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extern int sysctl_tcp_base_mss;
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extern int sysctl_tcp_workaround_signed_windows;
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extern atomic_t tcp_memory_allocated;
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extern atomic_t tcp_sockets_allocated;
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@ -680,7 +680,14 @@ ctl_table ipv4_table[] = {
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.mode = 0644,
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.proc_handler = &proc_dointvec,
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},
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{
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.ctl_name = NET_IPV4_TCP_WORKAROUND_SIGNED_WINDOWS,
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.procname = "tcp_workaround_signed_windows",
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.data = &sysctl_tcp_workaround_signed_windows,
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.maxlen = sizeof(int),
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.mode = 0644,
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.proc_handler = &proc_dointvec
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},
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{ .ctl_name = 0 }
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};
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@ -45,6 +45,11 @@
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/* People can turn this off for buggy TCP's found in printers etc. */
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int sysctl_tcp_retrans_collapse = 1;
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/* People can turn this on to work with those rare, broken TCPs that
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* interpret the window field as a signed quantity.
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*/
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int sysctl_tcp_workaround_signed_windows = 0;
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/* This limits the percentage of the congestion window which we
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* will allow a single TSO frame to consume. Building TSO frames
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* which are too large can cause TCP streams to be bursty.
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@ -177,12 +182,18 @@ void tcp_select_initial_window(int __space, __u32 mss,
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space = (space / mss) * mss;
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/* NOTE: offering an initial window larger than 32767
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* will break some buggy TCP stacks. We try to be nice.
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* If we are not window scaling, then this truncates
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* our initial window offering to 32k. There should also
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* be a sysctl option to stop being nice.
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* will break some buggy TCP stacks. If the admin tells us
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* it is likely we could be speaking with such a buggy stack
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* we will truncate our initial window offering to 32K-1
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* unless the remote has sent us a window scaling option,
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* which we interpret as a sign the remote TCP is not
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* misinterpreting the window field as a signed quantity.
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*/
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if (sysctl_tcp_workaround_signed_windows)
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(*rcv_wnd) = min(space, MAX_TCP_WINDOW);
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else
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(*rcv_wnd) = space;
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(*rcv_wscale) = 0;
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if (wscale_ok) {
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/* Set window scaling on max possible window
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@ -241,7 +252,7 @@ static u16 tcp_select_window(struct sock *sk)
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/* Make sure we do not exceed the maximum possible
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* scaled window.
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*/
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if (!tp->rx_opt.rcv_wscale)
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if (!tp->rx_opt.rcv_wscale && sysctl_tcp_workaround_signed_windows)
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new_win = min(new_win, MAX_TCP_WINDOW);
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else
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new_win = min(new_win, (65535U << tp->rx_opt.rcv_wscale));
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