ivshmem: Rely on server sending the ID right after the version

The protocol specification (ivshmem-spec.txt, formerly
ivshmem_device_spec.txt) has always required the ID message to be sent
right at the beginning, and ivshmem-server has always complied.  The
device, however, accepts it out of order.  If an interrupt setup
arrived before it, though, it would be misinterpreted as connect
notification.  Fix the latent bug by relying on the spec and
ivshmem-server's actual behavior.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <1458066895-20632-28-git-send-email-armbru@redhat.com>

1 files changed, 24 insertions, 3 deletions

diff --git a/hw/misc/ivshmem.c b/hw/misc/ivshmem.c
index 7f439c3b04..da32a74004 100644
--- a/hw/misc/ivshmem.c
+++ b/hw/misc/ivshmem.c
@@ -653,8 +653,6 @@ static void process_msg(IVShmemState *s, int64_t msg, int fd, Error **errp)
 
     if (fd >= 0) {
         process_msg_connect(s, msg, fd, errp);
-    } else if (s->vm_id == -1) {
-        s->vm_id = msg;
     } else {
         process_msg_disconnect(s, msg, errp);
     }
@@ -722,6 +720,30 @@ static void ivshmem_recv_setup(IVShmemState *s, Error **errp)
     }
 
     /*
+     * ivshmem-server sends the remaining initial messages in a fixed
+     * order, but the device has always accepted them in any order.
+     * Stay as compatible as practical, just in case people use
+     * servers that behave differently.
+     */
+
+    /*
+     * ivshmem_device_spec.txt has always required the ID message
+     * right here, and ivshmem-server has always complied.  However,
+     * older versions of the device accepted it out of order, but
+     * broke when an interrupt setup message arrived before it.
+     */
+    msg = ivshmem_recv_msg(s, &fd, &err);
+    if (err) {
+        error_propagate(errp, err);
+        return;
+    }
+    if (fd != -1 || msg < 0 || msg > IVSHMEM_MAX_PEERS) {
+        error_setg(errp, "server sent invalid ID message");
+        return;
+    }
+    s->vm_id = msg;
+
+    /*
      * Receive more messages until we got shared memory.
      */
     do {
@@ -956,7 +978,6 @@ static void pci_ivshmem_realize(PCIDevice *dev, Error **errp)
 
         /* we allocate enough space for 16 peers and grow as needed */
         resize_peers(s, 16);
-        s->vm_id = -1;
 
         pci_register_bar(dev, 2, attr, &s->bar);