Do not realloc strings, which are already in the hashmap as keys

This prevents corruption of the hashmap, because we would free() the
keys in the hashmap, if the unit is already in there, with the same
cgroup path.

src/core/cgroup.c

@@ -382,6 +382,7 @@ static CGroupControllerMask unit_get_siblings_mask(Unit *u) {
 static int unit_create_cgroups(Unit *u, CGroupControllerMask mask) {
         char *path = NULL;
         int r;
+        bool is_in_hash = false;
 
         assert(u);
 
@@ -390,8 +391,14 @@ static int unit_create_cgroups(Unit *u, CGroupControllerMask mask) {
                 return -ENOMEM;
 
         r = hashmap_put(u->manager->cgroup_unit, path, u);
-        if (r < 0)
+        if (r == 0)
+                is_in_hash = true;
+
+        if (r < 0) {
+                free(path);
+                log_error("cgroup %s exists already: %s", path, strerror(-r));
                 return r;
+        }
 
         /* First, create our own group */
         r = cg_create_with_mask(mask, path);
@@ -405,9 +412,12 @@ static int unit_create_cgroups(Unit *u, CGroupControllerMask mask) {
                         log_error("Failed to migrate cgroup %s: %s", path, strerror(-r));
         }
 
-        /* And remember the new data */
-        free(u->cgroup_path);
-        u->cgroup_path = path;
+        if (!is_in_hash) {
+                /* And remember the new data */
+                free(u->cgroup_path);
+                u->cgroup_path = path;
+        }
+
         u->cgroup_realized = true;
         u->cgroup_mask = mask;
 

src/core/unit.c

@@ -2329,7 +2329,7 @@ int unit_deserialize(Unit *u, FILE *f, FDSet *fds) {
                         free(u->cgroup_path);
                         u->cgroup_path = s;
 
-                        hashmap_put(u->manager->cgroup_unit, s, u);
+                        assert(hashmap_put(u->manager->cgroup_unit, s, u) == 1);
                         continue;
                 }