ssh: Don't crash if either host or path is not specified.

$ ./qemu-img create -f qcow2 overlay \
    -b 'json: { "file.driver":"ssh",
                "file.host":"localhost",
                "file.host_key_check":"no" }'
qemu-img: qobject/qdict.c:193: qdict_get_obj: Assertion `obj != ((void *)0)' failed.
Aborted

A similar crash also happens if the file.host field is omitted.

https://bugzilla.redhat.com/show_bug.cgi?id=1147343

Bug found and reported by Jun Li.
Signed-off-by: NRichard W.M. Jones <rjones@redhat.com>
Reviewed-by: NGonglei <arei.gonglei@huawei.com>
Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com>

block/ssh.c

@@ -517,6 +517,11 @@ static int connect_to_ssh(BDRVSSHState *s, QDict *options,
     const char *host, *user, *path, *host_key_check;
     int port;
 
+    if (!qdict_haskey(options, "host")) {
+        ret = -EINVAL;
+        error_setg(errp, "No hostname was specified");
+        goto err;
+    }
     host = qdict_get_str(options, "host");
 
     if (qdict_haskey(options, "port")) {
@@ -525,6 +530,11 @@ static int connect_to_ssh(BDRVSSHState *s, QDict *options,
         port = 22;
     }
 
+    if (!qdict_haskey(options, "path")) {
+        ret = -EINVAL;
+        error_setg(errp, "No path was specified");
+        goto err;
+    }
     path = qdict_get_str(options, "path");
 
     if (qdict_haskey(options, "user")) {