tcp, tcp_splice: Fix port remapping for inbound, spliced connections

In pasta mode, when we receive a new inbound connection, we need to
select a socket that was created in the namespace to proceed and
connect() it to its final destination.

The existing condition might pick a wrong socket, though, if the
destination port is remapped, because we'll check the bitmap of
inbound ports using the remapped port (stored in the epoll reference)
as index, and not the original port.

Instead of using the port bitmap for this purpose, store this
information in the epoll reference itself, by adding a new 'outbound'
bit, that's set if the listening socket was created the namespace,
and unset otherwise.

Then, use this bit to pick a socket on the right side.

Suggested-by: David Gibson <david@gibson.dropbear.id.au>
Fixes: 33482d5bf293 ("passt: Add PASTA mode, major rework")
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>

1 files changed, 3 insertions, 4 deletions

diff --git a/tcp.c b/tcp.c
index 63153b6..0d4ce57 100644
--- a/tcp.c
+++ b/tcp.c
@@ -3084,15 +3084,14 @@ void tcp_sock_handler(struct ctx *c, union epoll_ref ref, uint32_t events,
 void tcp_sock_init(const struct ctx *c, int ns, sa_family_t af,
 		   const void *addr, const char *ifname, in_port_t port)
 {
-	union tcp_epoll_ref tref = { .tcp.listen = 1 };
+	union tcp_epoll_ref tref = { .tcp.listen = 1, .tcp.outbound = ns };
 	const void *bind_addr;
 	int s;
 
-	if (ns) {
+	if (ns)
 		tref.tcp.index = (in_port_t)(port + c->tcp.fwd_out.delta[port]);
-	} else {
+	else
 		tref.tcp.index = (in_port_t)(port + c->tcp.fwd_in.delta[port]);
-	}
 
 	if (af == AF_INET || af == AF_UNSPEC) {
 		if (!addr && c->mode == MODE_PASTA)