[CRIU] [PATCH 1/2] tcp: allow to enable repair mode for sockets in closing states

[Andrey Vagin]

The repair mode is used for dumping state of tcp connections
(sequence numbers, queues, options, etc).

Currently the repair mode can be enalbed only for sockets in the
TCP_ESTABLISHED state. If a socket in another state, its internal
state can not be dumped.

Same time there is no guarantee that a connection won't be in other
states when we are dumping it, thus to be able to dump and restore
such states we need to get rid of CLOSE,ESTABLISHED in-kernel
limitation.

I see nothing wrong to allow enabling of the repair mode for connected
sockets in any states.

Cc: "David S. Miller" <davem at davemloft.net>
Cc: Alexey Kuznetsov <kuznet at ms2.inr.ac.ru>
Cc: James Morris <jmorris at namei.org>
Cc: Hideaki YOSHIFUJI <yoshfuji at linux-ipv6.org>
Cc: Patrick McHardy <kaber at trash.net>
Cc: Eric Dumazet <edumazet at google.com>
Cc: Pavel Emelyanov <xemul at parallels.com>
Cc: Cyrill Gorcunov <gorcunov at openvz.org>
Signed-off-by: Andrey Vagin <avagin at openvz.org>
---
 net/ipv4/tcp.c | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 2c7e326..bcb1d59 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -1106,15 +1106,18 @@ int tcp_sendmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg,
 	}
 
 	if (unlikely(tp->repair)) {
+		err = -EINVAL;
+		if (tp->repair_queue == TCP_NO_QUEUE)
+			goto out_err;
+
+		if (sk->sk_state != TCP_ESTABLISHED)
+			goto out_err;
+
 		if (tp->repair_queue == TCP_RECV_QUEUE) {
 			copied = tcp_send_rcvq(sk, msg, size);
 			goto out;
 		}
 
-		err = -EINVAL;
-		if (tp->repair_queue == TCP_NO_QUEUE)
-			goto out_err;
-
 		/* 'common' sending to sendq */
 	}
 
@@ -2375,7 +2378,8 @@ void tcp_sock_destruct(struct sock *sk)
 static inline bool tcp_can_repair_sock(const struct sock *sk)
 {
 	return ns_capable(sock_net(sk)->user_ns, CAP_NET_ADMIN) &&
-		((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_ESTABLISHED));
+		!((1 << sk->sk_state) & (TCPF_LISTEN |
+					 TCPF_SYN_SENT | TCPF_SYN_RECV));
 }
 
 static int tcp_repair_options_est(struct tcp_sock *tp,
-- 
1.9.0