BUG/MINOR: proxy: fix email-alert leak on deinit() (2nd try)

As shown in GH #2608 and ("BUG/MEDIUM: proxy: fix email-alert invalid
free"), simply calling free_email_alert() from free_proxy() is not the
right thing to do.

In this patch, we reuse proxy->email_alert.set memory space to introduce
proxy->email_alert.flags in order to support 2 flags:
PR_EMAIL_ALERT_SET (to mimic proxy->email_alert.set) and
PR_EMAIL_ALERT_RESOLVED (set once init_email_alert() was called on the
proxy to resolve email_alert.mailer pointer).

Thanks to PR_EMAIL_ALERT_RESOLVED flag, free_email_alert() may now
properly handle the freeing of proxy email_alert settings: if the RESOLVED
flag is set, then it means the .email_alert.mailers.name parsing hint was
replaced by the actual mailers pointer, thus no free should be attempted.

No backport needed: as described in ("BUG/MEDIUM: proxy: fix email-alert
invalid free"), this historical leak is not sensitive as it cannot be
triggered during runtime.. thus given that the fix is not backport-
friendly, it's not worth the trouble.

include/haproxy/mailers-t.h

@@ -35,6 +35,13 @@
 #include <haproxy/tcpcheck-t.h>
 #include <haproxy/thread-t.h>
 
+/* flags for proxy.email_alert.flags */
+enum proxy_email_alert_flags {
+	PR_EMAIL_ALERT_NONE = 0,
+	PR_EMAIL_ALERT_SET,      /* set if email alert settings are present */
+	PR_EMAIL_ALERT_RESOLVED, /* set if email alert settings were resolved */
+};
+
 struct mailer {
 	char *id;
 	struct mailers *mailers;

include/haproxy/proxy-t.h

@@ -438,7 +438,7 @@ struct proxy {
 		char *myhostname;		/* Identity to use in HELO command sent to mailer */
 		int level;			/* Maximum syslog level of messages to send
 						 * email alerts for */
-		int set;			/* True if email_alert settings are present */
+		int flags;                      /* check mailers.h for available flags */
 		struct email_alertq *queues;	/* per-mailer alerts queues */
 	} email_alert;
 

src/cfgparse-listen.c

@@ -22,6 +22,7 @@
 #include <haproxy/http_htx.h>
 #include <haproxy/http_ext.h>
 #include <haproxy/http_rules.h>
+#include <haproxy/mailers-t.h>
 #include <haproxy/listener.h>
 #include <haproxy/log.h>
 #include <haproxy/peers.h>
@@ -974,7 +975,7 @@ int cfg_parse_listen(const char *file, int linenum, char **args, int kwm)
 			goto out;
 		}
 		/* Indicate that the email_alert is at least partially configured */
-		curproxy->email_alert.set = 1;
+		curproxy->email_alert.flags |= PR_EMAIL_ALERT_SET;
 	}/* end else if (!strcmp(args[0], "email-alert"))  */
 	else if (strcmp(args[0], "persist") == 0) {  /* persist */
 		if (*(args[1]) == 0) {

src/cfgparse.c

@@ -3067,7 +3067,7 @@ int check_config_validity()
 			}
 		}
 
-		if (curproxy->email_alert.set) {
+		if (curproxy->email_alert.flags & PR_EMAIL_ALERT_SET) {
 		    if (!(curproxy->email_alert.mailers.name && curproxy->email_alert.from && curproxy->email_alert.to)) {
 			    ha_warning("'email-alert' will be ignored for %s '%s' (the presence any of "
 				       "'email-alert from', 'email-alert level' 'email-alert mailers', "

src/mailers.c

@@ -157,6 +157,7 @@ int init_email_alert(struct mailers *mls, struct proxy *p, char **err)
 	mls->users++;
 	free(p->email_alert.mailers.name);
 	p->email_alert.mailers.m = mls;
+	p->email_alert.flags |= PR_EMAIL_ALERT_RESOLVED;
 	p->email_alert.queues    = queues;
 	return 0;
 
@@ -174,7 +175,8 @@ int init_email_alert(struct mailers *mls, struct proxy *p, char **err)
 
 void free_email_alert(struct proxy *p)
 {
-	ha_free(&p->email_alert.mailers.name);
+	if (!(p->email_alert.flags & PR_EMAIL_ALERT_RESOLVED))
+		ha_free(&p->email_alert.mailers.name);
 	ha_free(&p->email_alert.from);
 	ha_free(&p->email_alert.to);
 	ha_free(&p->email_alert.myhostname);

src/proxy.c

@@ -254,6 +254,8 @@ static inline void proxy_free_common(struct proxy *px)
 		LIST_DEL_INIT(&lf->list);
 
 	chunk_destroy(&px->log_tag);
+
+	free_email_alert(px);
 }
 
 void free_proxy(struct proxy *p)
@@ -1482,7 +1484,6 @@ void proxy_free_defaults(struct proxy *defproxy)
 
 	proxy_release_conf_errors(defproxy);
 	deinit_proxy_tcpcheck(defproxy);
-	free_email_alert(defproxy);
 
 	/* FIXME: we cannot free uri_auth because it might already be used by
 	 * another proxy (legacy code for stats URI ...). Refcount anyone ?
@@ -1791,6 +1792,7 @@ static int proxy_defproxy_cpy(struct proxy *curproxy, const struct proxy *defpro
 	if (defproxy->check_command)
 		curproxy->check_command = strdup(defproxy->check_command);
 
+	BUG_ON(curproxy->email_alert.flags & PR_EMAIL_ALERT_RESOLVED);
 	if (defproxy->email_alert.mailers.name)
 		curproxy->email_alert.mailers.name = strdup(defproxy->email_alert.mailers.name);
 	if (defproxy->email_alert.from)
@@ -1800,7 +1802,7 @@ static int proxy_defproxy_cpy(struct proxy *curproxy, const struct proxy *defpro
 	if (defproxy->email_alert.myhostname)
 		curproxy->email_alert.myhostname = strdup(defproxy->email_alert.myhostname);
 	curproxy->email_alert.level = defproxy->email_alert.level;
-	curproxy->email_alert.set = defproxy->email_alert.set;
+	curproxy->email_alert.flags = defproxy->email_alert.flags;
 
 	return 0;
 }