BUG/MEDIUM: stats: prevent crash if counters not alloc with dummy one

Define a per-thread counters allocated with the greatest size of any
stat module counters. This variable is named trash_counters.

When using a proxy without allocated counters, return the trash counters
from EXTRA_COUNTERS_GET instead of a dangling pointer to prevent
segfault.

This is useful for all the proxies used internally and not
belonging to the global proxy list. As these objects does not appears on
the stat report, it does not matter to use the dummy counters.

For this fix to be functional, the extra counters are explicitly
initialized to NULL on proxy/server/listener init functions.

Most notably, the crash has already been detected with the following
vtc:
- reg-tests/lua/txn_get_priv.vtc
- reg-tests/peers/tls_basic_sync.vtc
- reg-tests/peers/tls_basic_sync_wo_stkt_backend.vtc
There is probably other parts that may be impacted (SPOE for example).

This bug was introduced in the current release and do not need to be
backported. The faulty commits are
"MINOR: ssl: count client hello for stats" and
"MINOR: ssl: add counters for ssl sessions".

include/haproxy/stats-t.h

@@ -509,11 +509,15 @@ enum stats_domain_px_cap {
 	STATS_PX_CAP_MASK = 0xff
 };
 
+extern THREAD_LOCAL void *trash_counters;
+
 #define EXTRA_COUNTERS(name) \
 	struct extra_counters *name
 
 #define EXTRA_COUNTERS_GET(counters, mod) \
-	(void *)((counters)->data + (mod)->counters_off[(counters)->type])
+	(likely(counters) ? \
+		((void *)((counters)->data + (mod)->counters_off[(counters)->type])) : \
+		(trash_counters))
 
 #define EXTRA_COUNTERS_REGISTER(counters, ctype, alloc_failed_label) \
 	do {                                                         \

src/listener.c

@@ -623,6 +623,8 @@ int create_listeners(struct bind_conf *bc, const struct sockaddr_storage *ss,
 		if (fd != -1)
 			l->rx.flags |= RX_F_INHERITED;
 
+		l->extra_counters = NULL;
+
 		HA_SPIN_INIT(&l->lock);
 		_HA_ATOMIC_ADD(&jobs, 1);
 		_HA_ATOMIC_ADD(&listeners, 1);

src/proxy.c

@@ -1041,6 +1041,9 @@ void init_new_proxy(struct proxy *p)
 	/* Default to only allow L4 retries */
 	p->retry_type = PR_RE_CONN_FAILED;
 
+	p->extra_counters_fe = NULL;
+	p->extra_counters_be = NULL;
+
 	HA_RWLOCK_INIT(&p->lock);
 }
 

src/server.c

@@ -1742,6 +1742,8 @@ struct server *new_server(struct proxy *proxy)
 	srv->agent.proxy = proxy;
 	srv->xprt  = srv->check.xprt = srv->agent.xprt = xprt_get(XPRT_RAW);
 
+	srv->extra_counters = NULL;
+
 	/* please don't put default server settings here, they are set in
 	 * init_default_instance().
 	 */

src/stats.c

@@ -269,6 +269,8 @@ static struct list stats_module_list[STATS_DOMAIN_COUNT] = {
 	LIST_HEAD_INIT(stats_module_list[STATS_DOMAIN_DNS]),
 };
 
+THREAD_LOCAL void *trash_counters;
+
 static inline uint8_t stats_get_domain(uint32_t domain)
 {
 	return domain >> STATS_DOMAIN & STATS_DOMAIN_MASK;
@@ -4548,6 +4550,34 @@ static int allocate_stats_dns_postcheck(void)
 
 REGISTER_CONFIG_POSTPARSER("allocate-stats-dns", allocate_stats_dns_postcheck);
 
+static int allocate_trash_counters(void)
+{
+	struct stats_module *mod;
+	int domains[] = { STATS_DOMAIN_PROXY, STATS_DOMAIN_DNS }, i;
+	size_t max_counters_size = 0;
+
+	/* calculate the greatest counters used by any stats modules */
+	for (i = 0; i < STATS_DOMAIN_COUNT; ++i) {
+		list_for_each_entry(mod, &stats_module_list[domains[i]], list) {
+			max_counters_size = mod->counters_size > max_counters_size ?
+			                    mod->counters_size : max_counters_size;
+		}
+	}
+
+	/* allocate the trash with the size of the greatest counters */
+	if (max_counters_size) {
+		trash_counters = malloc(max_counters_size);
+		if (!trash_counters) {
+			ha_alert("stats: cannot allocate trash counters for statistics\n");
+			return 0;
+		}
+	}
+
+	return 1;
+}
+
+REGISTER_PER_THREAD_ALLOC(allocate_trash_counters);
+
 static void deinit_stats(void)
 {
 	int domains[] = { STATS_DOMAIN_PROXY, STATS_DOMAIN_DNS }, i;
@@ -4565,6 +4595,14 @@ static void deinit_stats(void)
 
 REGISTER_POST_DEINIT(deinit_stats);
 
+static void free_trash_counters(void)
+{
+	if (trash_counters)
+		free(trash_counters);
+}
+
+REGISTER_PER_THREAD_FREE(free_trash_counters);
+
 /* register cli keywords */
 static struct cli_kw_list cli_kws = {{ },{
 	{ { "clear", "counters",  NULL }, "clear counters : clear max statistics counters (add 'all' for all counters)", cli_parse_clear_counters, NULL, NULL },