reds: Check link header magic without waiting for the whole header

This allows the connection to early fail in case initial bytes
are not correct.
This allows for instance VNC client to graceful fail connecting
to a spice-server. This happens easily as the two protocols
share the same range of ports.

This resolves rhbz#1416692.

Signed-off-by: Frediano Ziglio <fziglio@redhat.com>
Acked-by: Christophe Fergeau <cfergeau@redhat.com>

1 files changed, 20 insertions, 8 deletions

diff --git a/server/reds.c b/server/reds.c
index 91504544..f439a366 100644
--- a/server/reds.c
+++ b/server/reds.c
@@ -2192,12 +2192,6 @@ static void reds_handle_read_header_done(void *opaque)
     header->minor_version = GUINT32_FROM_LE(header->minor_version);
     header->size = GUINT32_FROM_LE(header->size);
 
-    if (header->magic != SPICE_MAGIC) {
-        reds_send_link_error(link, SPICE_LINK_ERR_INVALID_MAGIC);
-        reds_link_free(link);
-        return;
-    }
-
     if (header->major_version != SPICE_VERSION_MAJOR) {
         if (header->major_version > 0) {
             reds_send_link_error(link, SPICE_LINK_ERR_VERSION_MISMATCH);
@@ -2227,13 +2221,31 @@ static void reds_handle_read_header_done(void *opaque)
                            link);
 }
 
+static void reds_handle_read_magic_done(void *opaque)
+{
+    RedLinkInfo *link = (RedLinkInfo *)opaque;
+    const SpiceLinkHeader *header = &link->link_header;
+
+    if (header->magic != SPICE_MAGIC) {
+        reds_send_link_error(link, SPICE_LINK_ERR_INVALID_MAGIC);
+        reds_link_free(link);
+        return;
+    }
+
+    reds_stream_async_read(link->stream,
+                           ((uint8_t *)&link->link_header) + sizeof(header->magic),
+                           sizeof(SpiceLinkHeader) - sizeof(header->magic),
+                           reds_handle_read_header_done,
+                           link);
+}
+
 static void reds_handle_new_link(RedLinkInfo *link)
 {
     reds_stream_set_async_error_handler(link->stream, reds_handle_link_error);
     reds_stream_async_read(link->stream,
                            (uint8_t *)&link->link_header,
-                           sizeof(SpiceLinkHeader),
-                           reds_handle_read_header_done,
+                           sizeof(link->link_header.magic),
+                           reds_handle_read_magic_done,
                            link);
 }