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>
This commit is contained in:
David Gibson
2023-08-11 15:12:22 +10:00
committed by Stefano Brivio
parent 3401644453
commit 6a6735ece4
4 changed files with 29 additions and 12 deletions

View File

@@ -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;