tcp: restore rcv_wscale in a repair mode (v2)

rcv_wscale is a symetric parameter with snd_wscale.

Both this parameters are set on a connection handshake.

Without this value a remote window size can not be interpreted correctly,
because a value from a packet should be shifted on rcv_wscale.

And one more thing is that wscale_ok should be set too.

This patch doesn't break a backward compatibility.
If someone uses it in a old scheme, a rcv window
will be restored with the same bug (rcv_wscale = 0).

v2: Save backward compatibility on big-endian system. Before
    the first two bytes were snd_wscale and the second two bytes were
    rcv_wscale. Now snd_wscale is opt_val & 0xFFFF and rcv_wscale >> 16.
    This approach is independent on byte ordering.

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>
CC: Pavel Emelyanov <xemul@parallels.com>
Signed-off-by: Andrew Vagin <avagin@openvz.org>
Acked-by: Pavel Emelyanov <xemul@parallels.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 10 insertions, 3 deletions

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index bf9a8ab29459..5f6419341821 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -2331,10 +2331,17 @@ static int tcp_repair_options_est(struct tcp_sock *tp,
                         tp->rx_opt.mss_clamp = opt.opt_val;
                         break;
                 case TCPOPT_WINDOW:
-                        if (opt.opt_val > 14)
-                                return -EFBIG;
+                        {
+                                u16 snd_wscale = opt.opt_val & 0xFFFF;
+                                u16 rcv_wscale = opt.opt_val >> 16;
+
+                                if (snd_wscale > 14 || rcv_wscale > 14)
+                                        return -EFBIG;
 
-                        tp->rx_opt.snd_wscale = opt.opt_val;
+                                tp->rx_opt.snd_wscale = snd_wscale;
+                                tp->rx_opt.rcv_wscale = rcv_wscale;
+                                tp->rx_opt.wscale_ok = 1;
+                        }
                         break;
                 case TCPOPT_SACK_PERM:
                         if (opt.opt_val != 0)