vmd(8): fix use of qcow base images.

The vm process was prematurely setting device fds to not close-on-exec
and then trying to close(2) them after the fork(2) of the device
process.

This caused a reuse of an fd for one of the socketpair(2)'s for
communication between vm and device. Having device processes close(2)
other device fds after fork would break the socketpair, causing the
device to fail during startup post-exec when trying to receive its
device state from the parent vm process.

Instead, mark the fds to not close on exec post-fork(2) call allowing
other device fds to be closed automatically and avoid closing by
the tracked fd.

Reported by solene@. OK tb@.

1 files changed, 10 insertions, 34 deletions

diff --git a/usr.sbin/vmd/virtio.c b/usr.sbin/vmd/virtio.c
index 6167a7764cb..a58e3511543 100644
--- a/usr.sbin/vmd/virtio.c
+++ b/usr.sbin/vmd/virtio.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: virtio.c,v 1.104 2023/07/13 18:31:59 dv Exp $	*/
+/*	$OpenBSD: virtio.c,v 1.105 2023/07/15 18:32:21 dv Exp $	*/
 
 /*
  * Copyright (c) 2015 Mike Larkin <mlarkin@openbsd.org>
@@ -1302,8 +1302,7 @@ virtio_dev_launch(struct vmd_vm *vm, struct virtio_dev *dev)
 	char *nargv[10], num[32], vmm_fd[32], t[2];
 	pid_t dev_pid;
 	int data_fds[VM_MAX_BASE_PER_DISK], sync_fds[2], async_fds[2], ret = 0;
-	size_t i, j, data_fds_sz, sz = 0;
-	struct virtio_dev *d = NULL;
+	size_t i, data_fds_sz, sz = 0;
 	struct viodev_msg msg;
 	struct imsg imsg;
 	struct imsgev *iev = &dev->sync_iev;
@@ -1349,17 +1348,6 @@ virtio_dev_launch(struct vmd_vm *vm, struct virtio_dev *dev)
 		goto err;
 	}
 
-	/* Keep data file descriptors open after exec. */
-	for (i = 0; i < data_fds_sz; i++) {
-		log_debug("%s: marking fd %d !close-on-exec", __func__,
-		    data_fds[i]);
-		if (fcntl(data_fds[i], F_SETFD, 0)) {
-			ret = errno;
-			log_warn("%s: fcntl", __func__);
-			goto err;
-		}
-	}
-
 	/* Fork... */
 	dev_pid = fork();
 	if (dev_pid == -1) {
@@ -1459,26 +1447,14 @@ virtio_dev_launch(struct vmd_vm *vm, struct virtio_dev *dev)
 		close_fd(async_fds[0]);
 		close_fd(sync_fds[0]);
 
-		/*
-		 * Close any other device fd's we know aren't
-		 * ours. This releases any exclusive locks held on
-		 * things like disk images.
-		 */
-		SLIST_FOREACH(d, &virtio_devs, dev_next) {
-			if (d == dev)
-				continue;
-
-			switch (d->dev_type) {
-			case VMD_DEVTYPE_DISK:
-				for (j = 0; j < d->vioblk.ndisk_fd; j++)
-					close_fd(d->vioblk.disk_fd[j]);
-				break;
-			case VMD_DEVTYPE_NET:
-				close_fd(d->vionet.data_fd);
-				break;
-			default:
-				fatalx("%s: invalid device type '%c'",
-				    __func__, d->dev_type);
+		/* Keep data file descriptors open after exec. */
+		for (i = 0; i < data_fds_sz; i++) {
+			log_debug("%s: marking fd %d !close-on-exec", __func__,
+			    data_fds[i]);
+			if (fcntl(data_fds[i], F_SETFD, 0)) {
+				ret = errno;
+				log_warn("%s: fcntl", __func__);
+				goto err;
 			}
 		}