tcp: add an ability to dump and restore window parameters

We found that sometimes a restored tcp socket doesn't work.

A reason of this bug is incorrect window parameters and in this case
tcp_acceptable_seq() returns tcp_wnd_end(tp) instead of tp->snd_nxt. The
other side drops packets with this seq, because seq is less than
tp->rcv_nxt ( tcp_sequence() ).

Data from a send queue is sent only if there is enough space in a
window, so when we restore unacked data, we need to expand a window to
fit this data.

This was in a first version of this patch:
"tcp: extend window to fit all restored unacked data in a send queue"

Then Alexey recommended me to restore window parameters instead of
adjusted them according with data in a sent queue. This sounds resonable.

rcv_wnd has to be restored, because it was reported to another side
and the offered window is never shrunk.
One of reasons why we need to restore snd_wnd was described above.

Cc: Pavel Emelyanov <xemul@parallels.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>
Cc: James Morris <jmorris@namei.org>
Cc: Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>
Cc: Patrick McHardy <kaber@trash.net>
Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 67 insertions, 0 deletions

diff --git a/include/uapi/linux/tcp.h b/include/uapi/linux/tcp.h
index 53e8e3fe6b1b..482898fc433a 100644
--- a/include/uapi/linux/tcp.h
+++ b/include/uapi/linux/tcp.h
@@ -115,12 +115,22 @@ enum {
 #define TCP_CC_INFO             26      /* Get Congestion Control (optional) info */
 #define TCP_SAVE_SYN            27      /* Record SYN headers for new connections */
 #define TCP_SAVED_SYN           28      /* Get SYN headers recorded for connection */
+#define TCP_REPAIR_WINDOW       29      /* Get/set window parameters */
 
 struct tcp_repair_opt {
         __u32   opt_code;
         __u32   opt_val;
 };
 
+struct tcp_repair_window {
+        __u32   snd_wl1;
+        __u32   snd_wnd;
+        __u32   max_window;
+
+        __u32   rcv_wnd;
+        __u32   rcv_wup;
+};
+
 enum {
         TCP_NO_QUEUE,
         TCP_RECV_QUEUE,
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 5c7ed147449c..108ef2a6665c 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -2277,6 +2277,38 @@ static inline bool tcp_can_repair_sock(const struct sock *sk)
                 ((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_ESTABLISHED));
 }
 
+static int tcp_repair_set_window(struct tcp_sock *tp, char __user *optbuf, int len)
+{
+        struct tcp_repair_window opt;
+
+        if (!tp->repair)
+                return -EPERM;
+
+        if (len != sizeof(opt))
+                return -EINVAL;
+
+        if (copy_from_user(&opt, optbuf, sizeof(opt)))
+                return -EFAULT;
+
+        if (opt.max_window < opt.snd_wnd)
+                return -EINVAL;
+
+        if (after(opt.snd_wl1, tp->rcv_nxt + opt.rcv_wnd))
+                return -EINVAL;
+
+        if (after(opt.rcv_wup, tp->rcv_nxt))
+                return -EINVAL;
+
+        tp->snd_wl1     = opt.snd_wl1;
+        tp->snd_wnd     = opt.snd_wnd;
+        tp->max_window  = opt.max_window;
+
+        tp->rcv_wnd     = opt.rcv_wnd;
+        tp->rcv_wup     = opt.rcv_wup;
+
+        return 0;
+}
+
 static int tcp_repair_options_est(struct tcp_sock *tp,
                 struct tcp_repair_opt __user *optbuf, unsigned int len)
 {
@@ -2604,6 +2636,9 @@ static int do_tcp_setsockopt(struct sock *sk, int level,
                 else
                         tp->tsoffset = val - tcp_time_stamp;
                 break;
+        case TCP_REPAIR_WINDOW:
+                err = tcp_repair_set_window(tp, optval, optlen);
+                break;
         case TCP_NOTSENT_LOWAT:
                 tp->notsent_lowat = val;
                 sk->sk_write_space(sk);
@@ -2860,6 +2895,28 @@ static int do_tcp_getsockopt(struct sock *sk, int level,
                         return -EINVAL;
                 break;
 
+        case TCP_REPAIR_WINDOW: {
+                struct tcp_repair_window opt;
+
+                if (get_user(len, optlen))
+                        return -EFAULT;
+
+                if (len != sizeof(opt))
+                        return -EINVAL;
+
+                if (!tp->repair)
+                        return -EPERM;
+
+                opt.snd_wl1     = tp->snd_wl1;
+                opt.snd_wnd     = tp->snd_wnd;
+                opt.max_window  = tp->max_window;
+                opt.rcv_wnd     = tp->rcv_wnd;
+                opt.rcv_wup     = tp->rcv_wup;
+
+                if (copy_to_user(optval, &opt, len))
+                        return -EFAULT;
+                return 0;
+        }
         case TCP_QUEUE_SEQ:
                 if (tp->repair_queue == TCP_SEND_QUEUE)
                         val = tp->write_seq;