Make maximum clipboard buffer lenght configurable

fixes: QubesOS/qubes-issues#9296

gui-daemon/guid.conf

@@ -80,4 +80,9 @@ global: {
   # Timeout when waiting for qubes-gui-agent
   #
   # startup_timeout = 45;
+
+  # Inter-qube clipboard maximum character limit. This could be between 32000 to
+  # 16000000 characters. Default is 256000 characters.
+  #
+  # max_clipboard_size = 256000
 }

gui-daemon/xside.c

@@ -939,8 +939,8 @@ static int run_clipboard_rpc(Ghandles * g, enum clipboard_op op) {
             }
             umask(old_umask);
             if (op == CLIPBOARD_COPY) {
-                rl.rlim_cur = MAX_CLIPBOARD_SIZE;
-                rl.rlim_max = MAX_CLIPBOARD_SIZE;
+                rl.rlim_cur = g->clipboard_buffer_size;
+                rl.rlim_max = g->clipboard_buffer_size;
                 setrlimit(RLIMIT_FSIZE, &rl);
             }
             dup2(fd, 1);
@@ -1019,7 +1019,7 @@ static void handle_clipboard_data(Ghandles * g, unsigned int untrusted_len)
     if (g->log_level > 0)
         fprintf(stderr, "handle_clipboard_data, len=0x%x\n",
             untrusted_len);
-    if (untrusted_len > MAX_CLIPBOARD_SIZE) {
+    if (untrusted_len > g->clipboard_buffer_size) {
         fprintf(stderr, "clipboard data len 0x%x?\n",
             untrusted_len);
         exit(1);
@@ -4119,6 +4119,7 @@ static void load_default_config_values(Ghandles * g)
     g->copy_seq_key = XK_c;
     g->paste_seq_mask = ControlMask | ShiftMask;
     g->paste_seq_key = XK_v;
+    g->clipboard_buffer_size = DEFAULT_CLIPBOARD_BUFFER_SIZE;
     g->allow_fullscreen = 0;
     g->override_redirect_protection = 1;
     g->startup_timeout = 45;
@@ -4190,6 +4191,20 @@ static void parse_vm_config(Ghandles * g, config_setting_t * group)
                    &g->paste_seq_mask, &g->paste_seq_key);
     }
 
+    if ((setting =
+         config_setting_get_member(group, "max_clipboard_size"))) {
+        int value = config_setting_get_int(setting);
+        if (value > MAX_CLIPBOARD_BUFFER_SIZE || value < MIN_CLIPBOARD_BUFFER_SIZE) {
+            fprintf(stderr,
+                    "unsupported value ‘%d’ for max_clipboard_size "
+                    "(must be between %d to %d characters.\n",
+                    value, MAX_CLIPBOARD_BUFFER_SIZE, MIN_CLIPBOARD_BUFFER_SIZE);
+            exit(1);
+        } else {
+            g->clipboard_buffer_size = value;
+        }
+    }
+
     if ((setting =
          config_setting_get_member(group, "allow_utf8_titles"))) {
         g->allow_utf8_titles = config_setting_get_bool(setting);
@@ -4237,7 +4252,7 @@ static void parse_vm_config(Ghandles * g, config_setting_t * group)
             g->disable_override_redirect = 0;
         else {
             fprintf(stderr,
-                    "unsupported value ‘%s’ for override_redirect (must be ‘disabled’ or ‘allow’\n",
+                    "unsupported value ‘%s’ for override_redirect (must be ‘disabled’ or ‘allow’)\n",
                     value);
             exit(1);
         }

gui-daemon/xside.h

@@ -51,6 +51,11 @@
 #define QUBES_SERVICE_EVAL_SIMPLE "policy.EvalSimple"
 #define QUBES_SERVICE_EVAL_GUI "policy.EvalGUI"
 
+/* default, minimum and maximum clipboard buffer lenght */
+#define DEFAULT_CLIPBOARD_BUFFER_SIZE = 256000
+#define MIN_CLIPBOARD_BUFFER_SIZE = 32000
+#define MAX_CLIPBOARD_BUFFER_SIZE = 16000000
+
 /* default width of forced colorful border */
 #define BORDER_WIDTH 2
 
@@ -218,6 +223,7 @@ struct _global_handles {
     KeySym copy_seq_key;    /* key for secure-copy key sequence */
     int paste_seq_mask;    /* modifiers mask for secure-paste key sequence */
     KeySym paste_seq_key;    /* key for secure-paste key sequence */
+    int clipboard_buffer_size;    /* maximum clipboard character limit */
     int qrexec_clipboard;    /* 0: use GUI protocol to fetch/put clipboard, 1: use qrexec */
     int use_kdialog;    /* use kdialog for prompts (default on KDE) or zenity (default on non-KDE) */
     int prefix_titles;     /* prefix windows titles with VM name (for WM without support for _QUBES_VMNAME property) */