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, 2 deletions

diff --git a/pasta.c b/pasta.c
index 1e84680..dbe8e8c 100644
--- a/pasta.c
+++ b/pasta.c
@@ -365,7 +365,10 @@ void pasta_ns_conf(struct ctx *c)
 int pasta_netns_quit_init(struct ctx *c)
 {
 	int flags = O_NONBLOCK | O_CLOEXEC;
-	struct epoll_event ev = { .events = EPOLLIN };
+	union epoll_ref ref = { .type = EPOLL_TYPE_NSQUIT };
+	struct epoll_event ev = {
+		.events = EPOLLIN
+	};
 	int inotify_fd;
 
 	if (c->mode != MODE_PASTA || c->no_netns_quit || !*c->netns_base)
@@ -381,7 +384,8 @@ int pasta_netns_quit_init(struct ctx *c)
 		return -1;
 	}
 
-	ev.data.fd = inotify_fd;
+	ref.fd = inotify_fd;
+	ev.data.u64 = ref.u64;
 	epoll_ctl(c->epollfd, EPOLL_CTL_ADD, inotify_fd, &ev);
 
 	return inotify_fd;