Re: when having to acquire an SA, ipsec drops the packet

[David Miller <davem@davemloft.net>]

From: James Morris <jmorris@namei.org>
Date: Thu, 1 Feb 2007 18:44:48 -0500 (EST)

> A quick & dirty solution, which is what I think the BSD kernels do, is to 
> still drop the packet but just not return an error to the app.  The app 
> then just sees a slight delay on the initial connection, as if a DNS 
> lookup took a bit longer than usual.

I have another idea.

Why don't we just flat-out ignore MSG_DONTWAIT for the socket
visible cases, and handle connect() similarly?

I think this is (just barely) legal, will be simple to implement, and
will leave us with semantics that look like:

1) Sockets never see -EAGAIN due to SA resolution.  They'll just
   pause until the route is resolved, even with O_NONBLOCK or
   MSG_DONTWAIT.

2) Asynchronous contexts such as ICMP replies and firewalling
   will still see the -EAGAIN and simply drop packets.

These sleeps are legal because all of the socket paths involved
have to be able to do lock_socket() (at a minimum) anyways.

Something like this (untested) on the ipv4 side, for example:

diff --git a/include/net/route.h b/include/net/route.h
index 486e37a..a8af632 100644
--- a/include/net/route.h
+++ b/include/net/route.h
@@ -146,7 +146,8 @@ static inline char rt_tos2priority(u8 tos)
 
 static inline int ip_route_connect(struct rtable **rp, __be32 dst,
 				   __be32 src, u32 tos, int oif, u8 protocol,
-				   __be16 sport, __be16 dport, struct sock *sk)
+				   __be16 sport, __be16 dport, struct sock *sk,
+				   int flags)
 {
 	struct flowi fl = { .oif = oif,
 			    .nl_u = { .ip4_u = { .daddr = dst,
@@ -168,7 +169,7 @@ static inline int ip_route_connect(struct rtable **rp, __be32 dst,
 		*rp = NULL;
 	}
 	security_sk_classify_flow(sk, &fl);
-	return ip_route_output_flow(rp, &fl, sk, 0);
+	return ip_route_output_flow(rp, &fl, sk, 1);
 }
 
 static inline int ip_route_newports(struct rtable **rp, u8 protocol,
diff --git a/net/dccp/ipv4.c b/net/dccp/ipv4.c
index 90c74b4..fa2c982 100644
--- a/net/dccp/ipv4.c
+++ b/net/dccp/ipv4.c
@@ -72,7 +72,7 @@ int dccp_v4_connect(struct sock *sk, struct sockaddr *uaddr, int addr_len)
 	tmp = ip_route_connect(&rt, nexthop, inet->saddr,
 			       RT_CONN_FLAGS(sk), sk->sk_bound_dev_if,
 			       IPPROTO_DCCP,
-			       inet->sport, usin->sin_port, sk);
+			       inet->sport, usin->sin_port, sk, 1);
 	if (tmp < 0)
 		return tmp;
 
diff --git a/net/ipv4/af_inet.c b/net/ipv4/af_inet.c
index 8640096..5750a2b 100644
--- a/net/ipv4/af_inet.c
+++ b/net/ipv4/af_inet.c
@@ -1007,7 +1007,7 @@ static int inet_sk_reselect_saddr(struct sock *sk)
 			       RT_CONN_FLAGS(sk),
 			       sk->sk_bound_dev_if,
 			       sk->sk_protocol,
-			       inet->sport, inet->dport, sk);
+			       inet->sport, inet->dport, sk, 0);
 	if (err)
 		return err;
 
diff --git a/net/ipv4/datagram.c b/net/ipv4/datagram.c
index 7b068a8..0072d79 100644
--- a/net/ipv4/datagram.c
+++ b/net/ipv4/datagram.c
@@ -49,7 +49,7 @@ int ip4_datagram_connect(struct sock *sk, struct sockaddr *uaddr, int addr_len)
 	err = ip_route_connect(&rt, usin->sin_addr.s_addr, saddr,
 			       RT_CONN_FLAGS(sk), oif,
 			       sk->sk_protocol,
-			       inet->sport, usin->sin_port, sk);
+			       inet->sport, usin->sin_port, sk, 1);
 	if (err)
 		return err;
 	if ((rt->rt_flags & RTCF_BROADCAST) && !sock_flag(sk, SOCK_BROADCAST)) {
diff --git a/net/ipv4/raw.c b/net/ipv4/raw.c
index a6c63bb..fed6a1e 100644
--- a/net/ipv4/raw.c
+++ b/net/ipv4/raw.c
@@ -489,7 +489,7 @@ static int raw_sendmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg,
 		}
 
 		security_sk_classify_flow(sk, &fl);
-		err = ip_route_output_flow(&rt, &fl, sk, !(msg->msg_flags&MSG_DONTWAIT));
+		err = ip_route_output_flow(&rt, &fl, sk, 1);
 	}
 	if (err)
 		goto done;
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index f061ec5..383e4b5 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -191,7 +191,7 @@ int tcp_v4_connect(struct sock *sk, struct sockaddr *uaddr, int addr_len)
 	tmp = ip_route_connect(&rt, nexthop, inet->saddr,
 			       RT_CONN_FLAGS(sk), sk->sk_bound_dev_if,
 			       IPPROTO_TCP,
-			       inet->sport, usin->sin_port, sk);
+			       inet->sport, usin->sin_port, sk, 1);
 	if (tmp < 0)
 		return tmp;
 
diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index cfff930..8b54c68 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -629,7 +629,7 @@ int udp_sendmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg,
 					       { .sport = inet->sport,
 						 .dport = dport } } };
 		security_sk_classify_flow(sk, &fl);
-		err = ip_route_output_flow(&rt, &fl, sk, !(msg->msg_flags&MSG_DONTWAIT));
+		err = ip_route_output_flow(&rt, &fl, sk, 1);
 		if (err)
 			goto out;