ui/vnc: Fix crash when specifying [vnc] without id in the config file

QEMU currently crashes when there is a [vnc] section in the config
file that does not have an "id = ..." line:

 $ echo "[vnc]" > /tmp/qemu.conf
 $ ./qemu-system-x86_64 -readconfig /tmp/qemu.conf
 qemu-system-x86_64: ../../devel/qemu/ui/vnc.c:4347: vnc_init_func:
  Assertion `id' failed.
 Aborted (core dumped)

The required "id" is only set up automatically while parsing the command
line, but not when reading the options from the config file.
Thus let's move code that automatically adds the id (if it does not
exist yet) to the init function that needs the id for the first time,
replacing the assert() statement there.

Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2836
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
Message-ID: <20250821145130.845104-1-thuth@redhat.com>

diff --git a/ui/vnc.c b/ui/vnc.c
index 68ca4a68e7a23fc41c1b3c662b622907e590bc83..9054fc812535bf2243df4c5c3da4d3e8d4220136 100644 (file)
--- a/ui/vnc.c
+++ b/ui/vnc.c
@@ -4309,8 +4309,9 @@ void vnc_display_add_client(const char *id, int csock, bool skipauth)
     }
 }
 
-static void vnc_auto_assign_id(QemuOptsList *olist, QemuOpts *opts)
+static char *vnc_auto_assign_id(QemuOpts *opts)
 {
+    QemuOptsList *olist = qemu_find_opts("vnc");
     int i = 2;
     char *id;
 
@@ -4320,23 +4321,18 @@ static void vnc_auto_assign_id(QemuOptsList *olist, QemuOpts *opts)
         id = g_strdup_printf("vnc%d", i++);
     }
     qemu_opts_set_id(opts, id);
+
+    return id;
 }
 
 void vnc_parse(const char *str)
 {
     QemuOptsList *olist = qemu_find_opts("vnc");
     QemuOpts *opts = qemu_opts_parse_noisily(olist, str, !is_help_option(str));
-    const char *id;
 
     if (!opts) {
         exit(1);
     }
-
-    id = qemu_opts_id(opts);
-    if (!id) {
-        /* auto-assign id if not present */
-        vnc_auto_assign_id(olist, opts);
-    }
 }
 
 int vnc_init_func(void *opaque, QemuOpts *opts, Error **errp)
@@ -4344,7 +4340,11 @@ int vnc_init_func(void *opaque, QemuOpts *opts, Error **errp)
     Error *local_err = NULL;
     char *id = (char *)qemu_opts_id(opts);
 
-    assert(id);
+    if (!id) {
+        /* auto-assign id if not present */
+        id = vnc_auto_assign_id(opts);
+    }
+
     vnc_display_init(id, &local_err);
     if (local_err) {
         error_propagate(errp, local_err);