udp: Re-use fixed bound sockets for packet forwarding when possible

When we look up udp_splice_to_ns[v6][src].target_sock in
udp_sock_handler_splice, all we really require of the socket is that it
be bound to port src in the pasta guest namespace.  Similarly for
udp_splice_to_init but bound in the init namespace.

Usually these sockets are created temporarily by udp_splice_connect() and
cleaned up by udp_timer().  However, depending on the -u and -U options its
possible we have a permanent socket bound to the relevant port created by
udp_sock_init().  If such a socket exists, we could use it instead of
creating a temporary one.  In fact we *must* use it, because we'll fail
trying to bind() a temporary one to the same port.

So allow this, store permanently bound sockets into udp_splice_to_{ns,init}
in udp_sock_init().  These won't get incorrectly removed by the timer
because we don't put a corresponding entry in the udp_act[] structure
which directs the timer what to clean up.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

1 files changed, 13 insertions, 9 deletions

diff --git a/udp.c b/udp.c
index 3fa74a1..4954a7c 100644
--- a/udp.c
+++ b/udp.c
@@ -153,7 +153,7 @@ struct udp_splice_flow {
 /* Port tracking, arrays indexed by packet source port (host order) */
 static struct udp_tap_port	udp_tap_map	[IP_VERSIONS][NUM_PORTS];
 
-/* Spliced "connections" indexed by originating source port (host order) */
+/* Spliced "connections" indexed by bound port of target_sock (host order) */
 static struct udp_splice_flow udp_splice_to_ns  [IP_VERSIONS][NUM_PORTS];
 static struct udp_splice_flow udp_splice_to_init[IP_VERSIONS][NUM_PORTS];
 
@@ -1095,16 +1095,18 @@ void udp_sock_init(const struct ctx *c, int ns, sa_family_t af,
 				bind_addr = &(uint32_t){ htonl(INADDR_LOOPBACK) };
 				uref.udp.splice = uref.udp.orig = true;
 
-				sock_l4(c, AF_INET, IPPROTO_UDP, bind_addr, ifname,
-					port, uref.u32);
+				s = sock_l4(c, AF_INET, IPPROTO_UDP, bind_addr,
+					    ifname, port, uref.u32);
+				udp_splice_to_init[V4][port].target_sock = s;
 			}
 		} else {
 			uref.udp.splice = uref.udp.orig = uref.udp.ns = true;
 
 			bind_addr = &(uint32_t){ htonl(INADDR_LOOPBACK) };
 
-			sock_l4(c, AF_INET, IPPROTO_UDP, bind_addr, ifname,
-				port, uref.u32);
+			s = sock_l4(c, AF_INET, IPPROTO_UDP, bind_addr,
+				    ifname, port, uref.u32);
+			udp_splice_to_ns[V4][port].target_sock = s;
 		}
 	}
 
@@ -1127,15 +1129,17 @@ void udp_sock_init(const struct ctx *c, int ns, sa_family_t af,
 				bind_addr = &in6addr_loopback;
 				uref.udp.splice = uref.udp.orig = true;
 
-				sock_l4(c, AF_INET6, IPPROTO_UDP, bind_addr, ifname,
-					port, uref.u32);
+				s = sock_l4(c, AF_INET6, IPPROTO_UDP, bind_addr,
+					    ifname, port, uref.u32);
+				udp_splice_to_init[V6][port].target_sock = s;
 			}
 		} else {
 			bind_addr = &in6addr_loopback;
 			uref.udp.splice = uref.udp.orig = uref.udp.ns = true;
 
-			sock_l4(c, AF_INET6, IPPROTO_UDP, bind_addr, ifname,
-				port, uref.u32);
+			s = sock_l4(c, AF_INET6, IPPROTO_UDP, bind_addr,
+				    ifname, port, uref.u32);
+			udp_splice_to_ns[V6][port].target_sock = s;
 		}
 	}
 }