Hello,
on NetBSD I'm tracking down an issue where xenstored never closes its
file descriptor to /var/run/xenstored/socket and instead loops at 100%
CPU on these descriptors.
xenstored loops because poll(2) returns a POLLIN event for these
descriptors but they are marked is_ignored = true.
I'm seeing this with xen 4.15, 4.13 and has also been reported with 4.11
with latest security patches.
It seems to have started with patches for XSA-115 (A user reported this
for 4.11)
I've tracked it down to a difference in poll(2) implementation; it seems
that linux will return something that is not (POLLIN|POLLOUT) when a
socket if closed; while NetBSD returns POLLIN (this matches the NetBSD's
man page).
First I think there may be a security issue here, as, even on linux it should
be possible for a client to cause a socket to go to the is_ignored state,
while still sending data and cause xenstored to go to a 100% CPU loop.
I think this is needed anyway:
--- xenstored_core.c.orig 2021-02-02 18:06:33.389316841 +0100
+++ xenstored_core.c 2021-02-02 19:27:43.761877371 +0100
@@ -397,9 +397,12 @@
!list_empty(&conn->out_list)))
*ptimeout = 0;
} else {
- short events = POLLIN|POLLPRI;
- if (!list_empty(&conn->out_list))
- events |= POLLOUT;
+ short events = 0;
+ if (!conn->is_ignored) {
+ events |= POLLIN|POLLPRI;
+ if (!list_empty(&conn->out_list))
+ events |= POLLOUT;
+ }
conn->pollfd_idx = set_fd(conn->fd, events);
}
}
Now I wonder if, on NetBSD at last, a read error or short read shouldn't
cause the socket to be closed, as with:
@@ -1561,6 +1565,8 @@
bad_client:
ignore_connection(conn);
+ /* we don't want to keep this connection alive */
+ talloc_free(conn);
}
static void handle_output(struct connection *conn)
what do you think ?
--
Manuel Bouyer <bou...@antioche.eu.org>
NetBSD: 26 ans d'experience feront toujours la difference
--
