[PULL 04/14] vhost-user: fix shared object lookup handler logic

["Michael S. Tsirkin" <mst@redhat.com>]

From: Albert Esteve <aesteve@redhat.com>

Refactor backend_read() function and add a reply_ack variable
to have the option for handlers to force tweak whether they should
send a reply or not without depending on VHOST_USER_NEED_REPLY_MASK
flag.

This fixes an issue with
vhost_user_backend_handle_shared_object_lookup() logic, as the
error path was not closing the backend channel correctly. So,
we can remove the reply call from within the handler, make
sure it returns early on errors as other handlers do and
set the reply_ack variable on backend_read() to true to ensure
that it will send a response, thus keeping the original intent.

Fixes: 1609476662 ("vhost-user: add shared_object msg")
Cc: qemu-stable@nongnu.org
Signed-off-by: Albert Esteve <aesteve@redhat.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Message-Id: <20251017072011.1874874-2-aesteve@redhat.com>
---
 hw/virtio/vhost-user.c | 40 +++++++++++++---------------------------
 1 file changed, 13 insertions(+), 27 deletions(-)

diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c
index aac98f898a..4b0fae12ae 100644
--- a/hw/virtio/vhost-user.c
+++ b/hw/virtio/vhost-user.c
@@ -1668,14 +1668,6 @@ static bool vhost_user_send_resp(QIOChannel *ioc, VhostUserHeader *hdr,
     return !qio_channel_writev_all(ioc, iov, ARRAY_SIZE(iov), errp);
 }
 
-static bool
-vhost_user_backend_send_dmabuf_fd(QIOChannel *ioc, VhostUserHeader *hdr,
-                                  VhostUserPayload *payload, Error **errp)
-{
-    hdr->size = sizeof(payload->u64);
-    return vhost_user_send_resp(ioc, hdr, payload, errp);
-}
-
 int vhost_user_get_shared_object(struct vhost_dev *dev, unsigned char *uuid,
                                  int *dmabuf_fd)
 {
@@ -1716,19 +1708,15 @@ int vhost_user_get_shared_object(struct vhost_dev *dev, unsigned char *uuid,
 
 static int
 vhost_user_backend_handle_shared_object_lookup(struct vhost_user *u,
-                                               QIOChannel *ioc,
-                                               VhostUserHeader *hdr,
-                                               VhostUserPayload *payload)
+                                               VhostUserShared *object)
 {
     QemuUUID uuid;
     CharFrontend *chr = u->user->chr;
-    Error *local_err = NULL;
     int dmabuf_fd = -1;
     int fd_num = 0;
 
-    memcpy(uuid.data, payload->object.uuid, sizeof(payload->object.uuid));
+    memcpy(uuid.data, object->uuid, sizeof(object->uuid));
 
-    payload->u64 = 0;
     switch (virtio_object_type(&uuid)) {
     case TYPE_DMABUF:
         dmabuf_fd = virtio_lookup_dmabuf(&uuid);
@@ -1737,18 +1725,16 @@ vhost_user_backend_handle_shared_object_lookup(struct vhost_user *u,
     {
         struct vhost_dev *dev = virtio_lookup_vhost_device(&uuid);
         if (dev == NULL) {
-            payload->u64 = -EINVAL;
-            break;
+            return -EINVAL;
         }
         int ret = vhost_user_get_shared_object(dev, uuid.data, &dmabuf_fd);
         if (ret < 0) {
-            payload->u64 = ret;
+            return ret;
         }
         break;
     }
     case TYPE_INVALID:
-        payload->u64 = -EINVAL;
-        break;
+        return -EINVAL;
     }
 
     if (dmabuf_fd != -1) {
@@ -1757,11 +1743,6 @@ vhost_user_backend_handle_shared_object_lookup(struct vhost_user *u,
 
     if (qemu_chr_fe_set_msgfds(chr, &dmabuf_fd, fd_num) < 0) {
         error_report("Failed to set msg fds.");
-        payload->u64 = -EINVAL;
-    }
-
-    if (!vhost_user_backend_send_dmabuf_fd(ioc, hdr, payload, &local_err)) {
-        error_report_err(local_err);
         return -EINVAL;
     }
 
@@ -1790,6 +1771,7 @@ static gboolean backend_read(QIOChannel *ioc, GIOCondition condition,
     struct iovec iov;
     g_autofree int *fd = NULL;
     size_t fdsize = 0;
+    bool reply_ack;
     int i;
 
     /* Read header */
@@ -1808,6 +1790,8 @@ static gboolean backend_read(QIOChannel *ioc, GIOCondition condition,
         goto err;
     }
 
+    reply_ack = hdr.flags & VHOST_USER_NEED_REPLY_MASK;
+
     /* Read payload */
     if (qio_channel_read_all(ioc, (char *) &payload, hdr.size, &local_err)) {
         error_report_err(local_err);
@@ -1833,8 +1817,10 @@ static gboolean backend_read(QIOChannel *ioc, GIOCondition condition,
                                                              &payload.object);
         break;
     case VHOST_USER_BACKEND_SHARED_OBJECT_LOOKUP:
-        ret = vhost_user_backend_handle_shared_object_lookup(dev->opaque, ioc,
-                                                             &hdr, &payload);
+        /* The backend always expects a response */
+        reply_ack = true;
+        ret = vhost_user_backend_handle_shared_object_lookup(dev->opaque,
+                                                             &payload.object);
         break;
     default:
         error_report("Received unexpected msg type: %d.", hdr.request);
@@ -1845,7 +1831,7 @@ static gboolean backend_read(QIOChannel *ioc, GIOCondition condition,
      * REPLY_ACK feature handling. Other reply types has to be managed
      * directly in their request handlers.
      */
-    if (hdr.flags & VHOST_USER_NEED_REPLY_MASK) {
+    if (reply_ack) {
         payload.u64 = !!ret;
         hdr.size = sizeof(payload.u64);
 
-- 
MST