xl: Fix adding additional config cmdline parameters

When checking the size of the buffer we hold for additional
config parameters passed on the command line we should take the
size of the to-be-added string into account. While at it, rework
the implementation to be cleaner and safer.

Signed-off-by: Andre Przywara <andre.przywara@amd.com>
Signed-off-by: Ian Jackson <ian.jackson@eu.citrix.com>

1 files changed, 5 insertions, 9 deletions

diff --git a/tools/libxl/xl_cmdimpl.c b/tools/libxl/xl_cmdimpl.c
index 6e2fce786d..547b2f6fa5 100644
--- a/tools/libxl/xl_cmdimpl.c
+++ b/tools/libxl/xl_cmdimpl.c
@@ -3179,21 +3179,17 @@ int main_create(int argc, char **argv)
         }
     }
 
-    memset(extra_config, 0, sizeof(extra_config));
-    while (optind < argc) {
-        if ((p = strchr(argv[optind], '='))) {
-            if (strlen(extra_config) + 1 < sizeof(extra_config)) {
-                if (strlen(extra_config))
-                    strcat(extra_config, "\n");
-                strcat(extra_config, argv[optind]);
-            }
+    extra_config[0] = '\0';
+    for (p = extra_config; optind < argc; optind++) {
+        if (strchr(argv[optind], '=') != NULL) {
+            p += snprintf(p, sizeof(extra_config) - (p - extra_config),
+                "%s\n", argv[optind]);
         } else if (!filename) {
             filename = argv[optind];
         } else {
             help("create");
             return 2;
         }
-        optind++;
     }
 
     memset(&dom_info, 0, sizeof(dom_info));