BUG/MAJOR: http: fix breakage of "reqdeny" causing random crashes

Commit 108b1dd ("MEDIUM: http: configurable http result codes for
http-request deny") introduced in 1.6-dev2 was incomplete. It introduced
a new field "rule_deny_status" into struct http_txn, which is filled only
by actions "http-request deny" and "http-request tarpit". It's then used
in the deny code path to emit the proper error message, but is used
uninitialized when the deny comes from a "reqdeny" rule, causing random
behaviours ranging from returning a 200, an empty response, or crashing
the process. Often upon startup only 200 was returned but after the fields
are used the crash happens. This can be sped up using -dM.

There's no need at all for storing this status in the http_txn struct
anyway since it's used immediately after being set. Let's store it in
a temporary variable instead which is passed as an argument to function
http_req_get_intercept_rule().

As an extra benefit, removing it from struct http_txn reduced the size
of this struct by 8 bytes.

This fix must be backported to 1.6 where the bug was detected. Special
thanks to Falco Schmutz for his detailed report including an exploitable
core and a reproducer.

--- include/types/proto_http.h.orig	Tue May 10 15:42:00 2016
+++ include/types/proto_http.h	Tue Jun 14 15:10:23 2016
@@ -362,7 +362,6 @@ struct http_txn {
 	unsigned int flags;             /* transaction flags */
 	enum http_meth_t meth;          /* HTTP method */
 	/* 1 unused byte here */
-	short rule_deny_status;         /* HTTP status from rule when denying */
 	short status;                   /* HTTP status from the server, negative if from proxy */
 
 	char *uri;                      /* first line if log needed, NULL otherwise */
Security fix for CVE-2016-5360
http://git.haproxy.org/?p=haproxy-1.6.git;a=commitdiff;h=60f01f8c89e4fb2723d5a9f2046286e699567e0b

--- src/proto_http.c.orig	Sun Dec 27 15:04:17 2015
+++ src/proto_http.c	Wed Jun 15 09:02:24 2016
@@ -3489,10 +3489,12 @@ static int http_transform_header(struct stream* s, str
  * further processing of the request (auth, deny, ...), and defaults to
  * HTTP_RULE_RES_STOP if it executed all rules or stopped on an allow, or
  * HTTP_RULE_RES_CONT if the last rule was reached. It may set the TX_CLTARPIT
- * on txn->flags if it encounters a tarpit rule.
+ * on txn->flags if it encounters a tarpit rule. If <deny_status> is not NULL
+ * and a deny/tarpit rule is matched, it will be filled with this rule's deny
+ * status.
  */
 enum rule_result
-http_req_get_intercept_rule(struct proxy *px, struct list *rules, struct stream *s)
+http_req_get_intercept_rule(struct proxy *px, struct list *rules, struct stream *s, int *deny_status)
 {
 	struct session *sess = strm_sess(s);
 	struct http_txn *txn = s->txn;
@@ -3538,12 +3540,14 @@ resume_execution:
 			return HTTP_RULE_RES_STOP;
 
 		case ACT_ACTION_DENY:
-			txn->rule_deny_status = rule->deny_status;
+			if (deny_status)
+				*deny_status = rule->deny_status;
 			return HTTP_RULE_RES_DENY;
 
 		case ACT_HTTP_REQ_TARPIT:
 			txn->flags |= TX_CLTARPIT;
-			txn->rule_deny_status = rule->deny_status;
+			if (deny_status)
+				*deny_status = rule->deny_status;
 			return HTTP_RULE_RES_DENY;
 
 		case ACT_HTTP_REQ_AUTH:
@@ -4302,6 +4306,7 @@ int http_process_req_common(struct stream *s, struct c
 	struct redirect_rule *rule;
 	struct cond_wordlist *wl;
 	enum rule_result verdict;
+	int deny_status = HTTP_ERR_403;
 
 	if (unlikely(msg->msg_state < HTTP_MSG_BODY)) {
 		/* we need more data */
@@ -4322,7 +4327,7 @@ int http_process_req_common(struct stream *s, struct c
 
 	/* evaluate http-request rules */
 	if (!LIST_ISEMPTY(&px->http_req_rules)) {
-		verdict = http_req_get_intercept_rule(px, &px->http_req_rules, s);
+		verdict = http_req_get_intercept_rule(px, &px->http_req_rules, s, &deny_status);
 
 		switch (verdict) {
 		case HTTP_RULE_RES_YIELD: /* some data miss, call the function later. */
@@ -4368,7 +4373,7 @@ int http_process_req_common(struct stream *s, struct c
 
 		/* parse the whole stats request and extract the relevant information */
 		http_handle_stats(s, req);
-		verdict = http_req_get_intercept_rule(px, &px->uri_auth->http_req_rules, s);
+		verdict = http_req_get_intercept_rule(px, &px->uri_auth->http_req_rules, s, &deny_status);
 		/* not all actions implemented: deny, allow, auth */
 
 		if (verdict == HTTP_RULE_RES_DENY) /* stats http-request deny */
@@ -4487,9 +4492,9 @@ int http_process_req_common(struct stream *s, struct c
 
  deny:	/* this request was blocked (denied) */
 	txn->flags |= TX_CLDENY;
-	txn->status = http_err_codes[txn->rule_deny_status];
+	txn->status = http_err_codes[deny_status];
 	s->logs.tv_request = now;
-	stream_int_retnclose(&s->si[0], http_error_message(s, txn->rule_deny_status));
+	stream_int_retnclose(&s->si[0], http_error_message(s, deny_status));
 	stream_inc_http_err_ctr(s);
 	sess->fe->fe_counters.denied_req++;
 	if (sess->fe != s->be)