conf: less error prone pointer access

These functions define pointer to their key shifted by a
number and guard access to it later via another variable.
Let's make this more explicit (and additionally have the
pointer be NULL in the case where it is not supposed to be
used).

Signed-off-by: Wolfgang Bumiller <w.bumiller@proxmox.com>

src/lxc/conf.c

@@ -4582,10 +4582,14 @@ int lxc_clear_cgroups(struct lxc_conf *c, const char *key)
 {
 	struct lxc_list *it,*next;
 	bool all = false;
-	const char *k = key + 11;
+	const char *k = NULL;
 
 	if (strcmp(key, "lxc.cgroup") == 0)
 		all = true;
+	else if (strncmp(key, "lxc.cgroup.", sizeof("lxc.cgroup.")-1) == 0)
+		k = key + sizeof("lxc.cgroup.")-1;
+	else
+		return -1;
 
 	lxc_list_for_each_safe(it, &c->cgroup, next) {
 		struct lxc_cgroup *cg = it->elem;
@@ -4634,11 +4638,15 @@ int lxc_clear_hooks(struct lxc_conf *c, const char *key)
 {
 	struct lxc_list *it,*next;
 	bool all = false, done = false;
-	const char *k = key + 9;
+	const char *k = NULL;
 	int i;
 
 	if (strcmp(key, "lxc.hook") == 0)
 		all = true;
+	else if (strncmp(key, "lxc.hook.", sizeof("lxc.hook.")-1) == 0)
+		k = key + sizeof("lxc.hook.")-1;
+	else
+		return -1;
 
 	for (i=0; i<NUM_LXC_HOOKS; i++) {
 		if (all || strcmp(k, lxchook_names[i]) == 0) {