shared/bootspec: avoid going through -1 when calculating array index

Coverity was complaining in CID#1399407 that config->entries might be used
while NULL. Let's add an assert to make sure it's not.

Also, let's quit early if we have no entries to loop through. The code was
not incorrect, but it's cleaner to avoid any negative indices.

1 files changed, 8 insertions, 6 deletions

diff --git a/src/shared/bootspec.c b/src/shared/bootspec.c
index afcf6f7ac1..64b2574a18 100644
--- a/src/shared/bootspec.c
+++ b/src/shared/bootspec.c
@@ -584,6 +584,12 @@ static int boot_entries_select_default(const BootConfig *config) {
         int i;
 
         assert(config);
+        assert(config->entries || config->n_entries == 0);
+
+        if (config->n_entries == 0) {
+                log_debug("Found no default boot entry :(");
+                return -1; /* -1 means "no default" */
+        }
 
         if (config->entry_oneshot)
                 for (i = config->n_entries - 1; i >= 0; i--)
@@ -609,12 +615,8 @@ static int boot_entries_select_default(const BootConfig *config) {
                                 return i;
                         }
 
-        if (config->n_entries > 0)
-                log_debug("Found default: last entry \"%s\"", config->entries[config->n_entries - 1].id);
-        else
-                log_debug("Found no default boot entry :(");
-
-        return config->n_entries - 1; /* -1 means "no default" */
+        log_debug("Found default: last entry \"%s\"", config->entries[config->n_entries - 1].id);
+        return config->n_entries - 1;
 }
 
 int boot_entries_load_config(