From 75bf8fb062e3f409d6252449dae631440aa95b72 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Corentin=20No=C3=ABl?= <corentin.noel@collabora.com>
Date: Sat, 28 Jan 2023 03:24:26 +0100
Subject: x-server: Avoid reusing the local X server if the hostname has
 changed

If the hostname has changed while using a local seat, we will fail to connect and
return to the greeter. Avoid this behavior by recreating the server.
---
 src/seat-local.c  |  4 +---
 src/seat-xvnc.c   |  4 +---
 src/x-authority.c |  8 --------
 src/x-authority.h |  2 --
 src/x-server.c    | 31 ++++++++++++++++++++++++++++++-
 src/x-server.h    |  2 ++
 6 files changed, 34 insertions(+), 17 deletions(-)

diff --git a/src/seat-local.c b/src/seat-local.c
index aa6a0b0f..90bb1455 100644
--- a/src/seat-local.c
+++ b/src/seat-local.c
@@ -175,9 +175,7 @@ create_x_server (SeatLocal *seat)
     if (command)
         x_server_local_set_command (x_server, command);
 
-    g_autofree gchar *number = g_strdup_printf ("%d", x_server_get_display_number (X_SERVER (x_server)));
-    g_autoptr(XAuthority) cookie = x_authority_new_local_cookie (number);
-    x_server_set_authority (X_SERVER (x_server), cookie);
+    x_server_set_local_authority (X_SERVER (x_server));
 
     const gchar *layout = seat_get_string_property (SEAT (seat), "xserver-layout");
     if (layout)
diff --git a/src/seat-xvnc.c b/src/seat-xvnc.c
index a726a9d6..47658df1 100644
--- a/src/seat-xvnc.c
+++ b/src/seat-xvnc.c
@@ -57,9 +57,7 @@ seat_xvnc_create_display_server (Seat *seat, Session *session)
 
     g_autoptr(XServerXVNC) x_server = x_server_xvnc_new ();
     priv->x_server = g_object_ref (x_server);
-    g_autofree gchar *number = g_strdup_printf ("%d", x_server_get_display_number (X_SERVER (x_server)));
-    g_autoptr(XAuthority) cookie = x_authority_new_local_cookie (number);
-    x_server_set_authority (X_SERVER (x_server), cookie);
+    x_server_set_local_authority (X_SERVER (x_server));
     x_server_xvnc_set_socket (x_server, g_socket_get_fd (priv->connection));
 
     const gchar *command = config_get_string (config_get_instance (), "VNCServer", "command");
diff --git a/src/x-authority.c b/src/x-authority.c
index a04f76a6..a312d6df 100644
--- a/src/x-authority.c
+++ b/src/x-authority.c
@@ -65,14 +65,6 @@ x_authority_new_cookie (guint16 family, const guint8 *address, gsize address_len
     return x_authority_new (family, address, address_length, number, "MIT-MAGIC-COOKIE-1", cookie, 16);
 }
 
-XAuthority *
-x_authority_new_local_cookie (const gchar *number)
-{
-    gchar hostname[1024];
-    gethostname (hostname, 1024);
-    return x_authority_new_cookie (XAUTH_FAMILY_LOCAL, (guint8 *) hostname, strlen (hostname), number);
-}
-
 void
 x_authority_set_family (XAuthority *auth, guint16 family)
 {
diff --git a/src/x-authority.h b/src/x-authority.h
index 1ddb8526..d9f0e0b2 100644
--- a/src/x-authority.h
+++ b/src/x-authority.h
@@ -55,8 +55,6 @@ XAuthority *x_authority_new (guint16 family, const guint8 *address, gsize addres
 
 XAuthority *x_authority_new_cookie (guint16 family, const guint8 *address, gsize address_length, const gchar *number);
 
-XAuthority *x_authority_new_local_cookie (const gchar *number);
-
 void x_authority_set_family (XAuthority *auth, guint16 family);
 
 guint16 x_authority_get_family (XAuthority *auth);
diff --git a/src/x-server.c b/src/x-server.c
index ae64808a..f17a842d 100644
--- a/src/x-server.c
+++ b/src/x-server.c
@@ -27,6 +27,9 @@ typedef struct
     /* Authority */
     XAuthority *authority;
 
+    /* Cached hostname for the authority */
+    gchar local_hostname[1024];
+
     /* Connection to this X server */
     xcb_connection_t *connection;
 } XServerPrivate;
@@ -91,6 +94,21 @@ x_server_set_authority (XServer *server, XAuthority *authority)
         priv->authority = g_object_ref (authority);
 }
 
+void
+x_server_set_local_authority (XServer *server)
+{
+    XServerPrivate *priv = x_server_get_instance_private (server);
+
+    g_return_if_fail (server != NULL);
+
+    g_clear_object (&priv->authority);
+    char display_number[12];
+    g_snprintf(display_number, sizeof(display_number), "%d", x_server_get_display_number (server));
+
+    gethostname (priv->local_hostname, 1024);
+    priv->authority = x_authority_new_cookie (XAUTH_FAMILY_LOCAL, (guint8 *) priv->local_hostname, strlen (priv->local_hostname), display_number);
+}
+
 XAuthority *
 x_server_get_authority (XServer *server)
 {
@@ -108,7 +126,18 @@ x_server_get_session_type (DisplayServer *server)
 static gboolean
 x_server_get_can_share (DisplayServer *server)
 {
-    return TRUE;
+    XServerPrivate *priv = x_server_get_instance_private ((XServer*) server);
+    gchar actual_local_hostname[1024];
+
+    g_return_val_if_fail (server != NULL, FALSE);
+
+    if (priv->local_hostname[0] == '\0')
+        return TRUE;
+
+    /* The XAuthority depends on the hostname so we can't share the display
+     * server if the hostname has been changed */
+    gethostname (actual_local_hostname, 1024);
+    return g_strcmp0 (actual_local_hostname, priv->local_hostname) == 0;
 }
 
 static gboolean
diff --git a/src/x-server.h b/src/x-server.h
index 18b91634..4d125b28 100644
--- a/src/x-server.h
+++ b/src/x-server.h
@@ -55,6 +55,8 @@ gsize x_server_get_authentication_data_length (XServer *server);
 
 void x_server_set_authority (XServer *server, XAuthority *authority);
 
+void x_server_set_local_authority (XServer *server);
+
 XAuthority *x_server_get_authority (XServer *server);
 
 G_END_DECLS
-- 
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