diff options
| -rw-r--r-- | Documentation/networking/ip-sysctl.rst | 15 | ||||
| -rw-r--r-- | include/net/netns/ipv4.h | 1 | ||||
| -rw-r--r-- | net/ipv4/sysctl_net_ipv4.c | 9 | ||||
| -rw-r--r-- | net/ipv4/tcp_ipv4.c | 2 | ||||
| -rw-r--r-- | net/ipv4/tcp_output.c | 60 |
5 files changed, 78 insertions, 9 deletions
diff --git a/Documentation/networking/ip-sysctl.rst b/Documentation/networking/ip-sysctl.rst index 366e2a5097d9..4a010a7cde7f 100644 --- a/Documentation/networking/ip-sysctl.rst +++ b/Documentation/networking/ip-sysctl.rst @@ -981,6 +981,21 @@ tcp_tw_reuse - INTEGER tcp_window_scaling - BOOLEAN Enable window scaling as defined in RFC1323. +tcp_shrink_window - BOOLEAN + This changes how the TCP receive window is calculated. + + RFC 7323, section 2.4, says there are instances when a retracted + window can be offered, and that TCP implementations MUST ensure + that they handle a shrinking window, as specified in RFC 1122. + + - 0 - Disabled. The window is never shrunk. + - 1 - Enabled. The window is shrunk when necessary to remain within + the memory limit set by autotuning (sk_rcvbuf). + This only occurs if a non-zero receive window + scaling factor is also in effect. + + Default: 0 + tcp_wmem - vector of 3 INTEGERs: min, default, max min: Amount of memory reserved for send buffers for TCP sockets. Each TCP socket has rights to use it due to fact of its birth. diff --git a/include/net/netns/ipv4.h b/include/net/netns/ipv4.h index a4efb7a2796c..f00374718159 100644 --- a/include/net/netns/ipv4.h +++ b/include/net/netns/ipv4.h @@ -65,6 +65,7 @@ struct netns_ipv4 { #endif bool fib_has_custom_local_routes; bool fib_offload_disabled; + u8 sysctl_tcp_shrink_window; #ifdef CONFIG_IP_ROUTE_CLASSID atomic_t fib_num_tclassid_users; #endif diff --git a/net/ipv4/sysctl_net_ipv4.c b/net/ipv4/sysctl_net_ipv4.c index 356afe54951c..2afb0870648b 100644 --- a/net/ipv4/sysctl_net_ipv4.c +++ b/net/ipv4/sysctl_net_ipv4.c @@ -1480,6 +1480,15 @@ static struct ctl_table ipv4_net_table[] = { .extra1 = SYSCTL_ZERO, .extra2 = &tcp_syn_linear_timeouts_max, }, + { + .procname = "tcp_shrink_window", + .data = &init_net.ipv4.sysctl_tcp_shrink_window, + .maxlen = sizeof(u8), + .mode = 0644, + .proc_handler = proc_dou8vec_minmax, + .extra1 = SYSCTL_ZERO, + .extra2 = SYSCTL_ONE, + }, { } }; diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c index 84a5d557dc1a..9213804b034f 100644 --- a/net/ipv4/tcp_ipv4.c +++ b/net/ipv4/tcp_ipv4.c @@ -3281,6 +3281,8 @@ static int __net_init tcp_sk_init(struct net *net) net->ipv4.tcp_congestion_control = &tcp_reno; net->ipv4.sysctl_tcp_syn_linear_timeouts = 4; + net->ipv4.sysctl_tcp_shrink_window = 0; + return 0; } diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c index 660eac4bf2a7..2cb39b6dad02 100644 --- a/net/ipv4/tcp_output.c +++ b/net/ipv4/tcp_output.c @@ -260,8 +260,8 @@ static u16 tcp_select_window(struct sock *sk) u32 old_win = tp->rcv_wnd; u32 cur_win = tcp_receive_window(tp); u32 new_win = __tcp_select_window(sk); + struct net *net = sock_net(sk); - /* Never shrink the offered window */ if (new_win < cur_win) { /* Danger Will Robinson! * Don't update rcv_wup/rcv_wnd here or else @@ -270,11 +270,14 @@ static u16 tcp_select_window(struct sock *sk) * * Relax Will Robinson. */ - if (new_win == 0) - NET_INC_STATS(sock_net(sk), - LINUX_MIB_TCPWANTZEROWINDOWADV); - new_win = ALIGN(cur_win, 1 << tp->rx_opt.rcv_wscale); + if (!READ_ONCE(net->ipv4.sysctl_tcp_shrink_window) || !tp->rx_opt.rcv_wscale) { + /* Never shrink the offered window */ + if (new_win == 0) + NET_INC_STATS(net, LINUX_MIB_TCPWANTZEROWINDOWADV); + new_win = ALIGN(cur_win, 1 << tp->rx_opt.rcv_wscale); + } } + tp->rcv_wnd = new_win; tp->rcv_wup = tp->rcv_nxt; @@ -282,7 +285,7 @@ static u16 tcp_select_window(struct sock *sk) * scaled window. */ if (!tp->rx_opt.rcv_wscale && - READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_workaround_signed_windows)) + READ_ONCE(net->ipv4.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)); @@ -294,10 +297,9 @@ static u16 tcp_select_window(struct sock *sk) if (new_win == 0) { tp->pred_flags = 0; if (old_win) - NET_INC_STATS(sock_net(sk), - LINUX_MIB_TCPTOZEROWINDOWADV); + NET_INC_STATS(net, LINUX_MIB_TCPTOZEROWINDOWADV); } else if (old_win == 0) { - NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPFROMZEROWINDOWADV); + NET_INC_STATS(net, LINUX_MIB_TCPFROMZEROWINDOWADV); } return new_win; @@ -2987,6 +2989,7 @@ u32 __tcp_select_window(struct sock *sk) { struct inet_connection_sock *icsk = inet_csk(sk); struct tcp_sock *tp = tcp_sk(sk); + struct net *net = sock_net(sk); /* MSS for the peer's data. Previous versions used mss_clamp * here. I don't know if the value based on our guesses * of peer's MSS is better for the performance. It's more correct @@ -3008,6 +3011,15 @@ u32 __tcp_select_window(struct sock *sk) if (mss <= 0) return 0; } + + /* Only allow window shrink if the sysctl is enabled and we have + * a non-zero scaling factor in effect. + */ + if (READ_ONCE(net->ipv4.sysctl_tcp_shrink_window) && tp->rx_opt.rcv_wscale) + goto shrink_window_allowed; + + /* do not allow window to shrink */ + if (free_space < (full_space >> 1)) { icsk->icsk_ack.quick = 0; @@ -3062,6 +3074,36 @@ u32 __tcp_select_window(struct sock *sk) } return window; + +shrink_window_allowed: + /* new window should always be an exact multiple of scaling factor */ + free_space = round_down(free_space, 1 << tp->rx_opt.rcv_wscale); + + if (free_space < (full_space >> 1)) { + icsk->icsk_ack.quick = 0; + + if (tcp_under_memory_pressure(sk)) + tcp_adjust_rcv_ssthresh(sk); + + /* if free space is too low, return a zero window */ + if (free_space < (allowed_space >> 4) || free_space < mss || + free_space < (1 << tp->rx_opt.rcv_wscale)) + return 0; + } + + if (free_space > tp->rcv_ssthresh) { + free_space = tp->rcv_ssthresh; + /* new window should always be an exact multiple of scaling factor + * + * For this case, we ALIGN "up" (increase free_space) because + * we know free_space is not zero here, it has been reduced from + * the memory-based limit, and rcv_ssthresh is not a hard limit + * (unlike sk_rcvbuf). + */ + free_space = ALIGN(free_space, (1 << tp->rx_opt.rcv_wscale)); + } + + return free_space; } void tcp_skb_collapse_tstamp(struct sk_buff *skb, |