epoll: Always use epoll_ref for the epoll data variable

epoll_ref contains a variety of information useful when handling epoll
events on our sockets, and we place it in the epoll_event data field
returned by epoll.  However, for a few other things we use the 'fd' field
in the standard union of types for that data field.

This actually introduces a bug which is vanishingly unlikely to hit in
practice, but very nasty if it ever did: theoretically if we had a very
large file descriptor number for fd_tap or fd_tap_listen it could overflow
into bits that overlap with the 'proto' field in epoll_ref.  With some
very bad luck this could mean that we mistakenly think an event on a
regular socket is an event on fd_tap or fd_tap_listen.

More practically, using different (but overlapping) fields of the
epoll_data means we can't unify dispatch for the various different objects
in the epoll.  Therefore use the same epoll_ref as the data for the tap
fds and the netns quit fd, adding new fd type values to describe them.

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

1 files changed, 6 insertions, 5 deletions

diff --git a/passt.c b/passt.c
index ae69478..45e9fbf 100644
--- a/passt.c
+++ b/passt.c
@@ -60,6 +60,8 @@ char *epoll_type_str[EPOLL_TYPE_MAX + 1] = {
 	[EPOLL_TYPE_UDP]	= "UDP socket",
 	[EPOLL_TYPE_ICMP]	= "ICMP socket",
 	[EPOLL_TYPE_ICMPV6]	= "ICMPv6 socket",
+	[EPOLL_TYPE_NSQUIT]	= "namespace inotify",
+	[EPOLL_TYPE_TAP]	= "tap device",
 };
 
 /**
@@ -328,12 +330,11 @@ loop:
 
 	for (i = 0; i < nfds; i++) {
 		union epoll_ref ref = *((union epoll_ref *)&events[i].data.u64);
-		int fd = events[i].data.fd;
 
-		if (fd == c.fd_tap || fd == c.fd_tap_listen)
-			tap_handler(&c, fd, events[i].events, &now);
-		else if (fd == quit_fd)
-			pasta_netns_quit_handler(&c, fd);
+		if (ref.type == EPOLL_TYPE_TAP)
+			tap_handler(&c, ref.fd, events[i].events, &now);
+		else if (ref.type == EPOLL_TYPE_NSQUIT)
+			pasta_netns_quit_handler(&c, quit_fd);
 		else
 			sock_handler(&c, ref, events[i].events, &now);
 	}