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-rw-r--r--Documentation/networking/ip-sysctl.txt7
-rw-r--r--include/linux/sysctl.h1
-rw-r--r--include/net/tcp.h1
-rw-r--r--net/ipv4/sysctl_net_ipv4.c9
-rw-r--r--net/ipv4/tcp_output.c23
5 files changed, 34 insertions, 7 deletions
diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt
index 651298ba019a..f12007b80a46 100644
--- a/Documentation/networking/ip-sysctl.txt
+++ b/Documentation/networking/ip-sysctl.txt
@@ -355,6 +355,13 @@ somaxconn - INTEGER
Defaults to 128. See also tcp_max_syn_backlog for additional tuning
for TCP sockets.
+tcp_workaround_signed_windows - BOOLEAN
+ If set, assume no receipt of a window scaling option means the
+ remote TCP is broken and treats the window as a signed quantity.
+ If unset, assume the remote TCP is not broken even if we do
+ not receive a window scaling option from them.
+ Default: 0
+
IP Variables:
ip_local_port_range - 2 INTEGERS
diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h
index 8754568a75d7..76eaeff76f82 100644
--- a/include/linux/sysctl.h
+++ b/include/linux/sysctl.h
@@ -402,6 +402,7 @@ enum
NET_IPV4_IPFRAG_MAX_DIST=112,
NET_TCP_MTU_PROBING=113,
NET_TCP_BASE_MSS=114,
+ NET_IPV4_TCP_WORKAROUND_SIGNED_WINDOWS=115,
};
enum {
diff --git a/include/net/tcp.h b/include/net/tcp.h
index 16879fa560de..457e224de468 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -224,6 +224,7 @@ extern int sysctl_tcp_tso_win_divisor;
extern int sysctl_tcp_abc;
extern int sysctl_tcp_mtu_probing;
extern int sysctl_tcp_base_mss;
+extern int sysctl_tcp_workaround_signed_windows;
extern atomic_t tcp_memory_allocated;
extern atomic_t tcp_sockets_allocated;
diff --git a/net/ipv4/sysctl_net_ipv4.c b/net/ipv4/sysctl_net_ipv4.c
index ebf2e0b363c4..6b6c3adfcf00 100644
--- a/net/ipv4/sysctl_net_ipv4.c
+++ b/net/ipv4/sysctl_net_ipv4.c
@@ -680,7 +680,14 @@ ctl_table ipv4_table[] = {
.mode = 0644,
.proc_handler = &proc_dointvec,
},
-
+ {
+ .ctl_name = NET_IPV4_TCP_WORKAROUND_SIGNED_WINDOWS,
+ .procname = "tcp_workaround_signed_windows",
+ .data = &sysctl_tcp_workaround_signed_windows,
+ .maxlen = sizeof(int),
+ .mode = 0644,
+ .proc_handler = &proc_dointvec
+ },
{ .ctl_name = 0 }
};
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 518e568b53f3..9d79546d384e 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -45,6 +45,11 @@
/* People can turn this off for buggy TCP's found in printers etc. */
int sysctl_tcp_retrans_collapse = 1;
+/* People can turn this on to work with those rare, broken TCPs that
+ * interpret the window field as a signed quantity.
+ */
+int sysctl_tcp_workaround_signed_windows = 0;
+
/* This limits the percentage of the congestion window which we
* will allow a single TSO frame to consume. Building TSO frames
* which are too large can cause TCP streams to be bursty.
@@ -177,12 +182,18 @@ void tcp_select_initial_window(int __space, __u32 mss,
space = (space / mss) * mss;
/* NOTE: offering an initial window larger than 32767
- * will break some buggy TCP stacks. We try to be nice.
- * If we are not window scaling, then this truncates
- * our initial window offering to 32k. There should also
- * be a sysctl option to stop being nice.
+ * will break some buggy TCP stacks. If the admin tells us
+ * it is likely we could be speaking with such a buggy stack
+ * we will truncate our initial window offering to 32K-1
+ * unless the remote has sent us a window scaling option,
+ * which we interpret as a sign the remote TCP is not
+ * misinterpreting the window field as a signed quantity.
*/
- (*rcv_wnd) = min(space, MAX_TCP_WINDOW);
+ if (sysctl_tcp_workaround_signed_windows)
+ (*rcv_wnd) = min(space, MAX_TCP_WINDOW);
+ else
+ (*rcv_wnd) = space;
+
(*rcv_wscale) = 0;
if (wscale_ok) {
/* Set window scaling on max possible window
@@ -241,7 +252,7 @@ static u16 tcp_select_window(struct sock *sk)
/* Make sure we do not exceed the maximum possible
* scaled window.
*/
- if (!tp->rx_opt.rcv_wscale)
+ if (!tp->rx_opt.rcv_wscale && sysctl_tcp_workaround_signed_windows)
new_win = min(new_win, MAX_TCP_WINDOW);
else
new_win = min(new_win, (65535U << tp->rx_opt.rcv_wscale));